Monday, December 27, 2010

Bosch Progressor U234X blade

My super-cheap Harbor Freight jigsaw used to cut horribly crookedly and non-squarely. The recommendation I was hearing was to get a circular saw, but I was scared of kickback. So I decided to try a good blade in the jigsaw.

I ordered a Bosch Progressor sampler pack from ebay, and loaded a U234X blade in the jigsaw. While I was at it, I noticed the jigsaw's shoe wasn't square and fixed it. I set medium speed, and turned off the orbital feature, and made a sample cut of 1/2" baltic birch ply against a guide. It cut very slowly, but once it was done the cut was quite straight and smooth. And only a touch of sanding would be needed. The squareness was off by about 0.3 degrees. (Maybe the shoe isn't quite square enough?)

All in all, it's good enough for me. No need for using a router or circular saw.

In the photo, the test cut I did is the front cut (the photo shows both sides of the cut). The side cuts were done with a friend's table saw. Those cuts are slightly straighter and perfectly square (as far as I can tell), but have a lot more tear-out.

The U234X (T234X is the T-shank version) blade is cool. It's 0.05" thick and has two alternating rows of teeth, one against each cutting surface, which smooth both sides of the kerf.

A 24" and an 8"

I went out last night to our club's observatory, and got to learn a bit of my way around controlling the observatory's 24" Ritchey-Chretien.  My plan was to look at clusters in M31.  I did all the observing in the 24" through the camera, with exposures from 5 to 200 seconds.  I started with a very quick and shapely image of the spiral galaxy M74 that I didn't save.  And M76, the Little Dumbbell, looked like its big cousin.  I tried for a galaxy cluster, but at my exposure times I could barely see anything.

Then I moved on to what I was primarily aiming at: the M31 clusters.  I did see G1, G76, G78, G81 and G280.  The hard part wasn't seeing the objects, but identifying them, as at the resolution of the camera I was using they all just looked like stars, as can be seen in my photo on the right, except maybe G1 (the bigger circles are just brighter stars).  G1 has two stars from our galaxy really close to it and looks like the head of Mickey Mouse, with the stars being its ears, which made it easy to identify.  The others I just had to correlate against SIMBAD images and the M31 clusters catalog in AstroInfo.  Since AstroInfo only goes up to magnitude 12.7 in stars, there were very few stars in each camera field of view to correlate with, but I think I did manage to identify all the objects by their relative positions to these stars.

I also looked at one open cluster in M31 for good measure: VDB0-B195D.  It looked like it had some detail around the bottom edge, though the supposed detail may just be foreground Milky Way stars.  The photo also captured NGC 206, a fragment of M31, and a bunch of prominent dark lanes in the M31 background.  None of these are amazing photos--they're more like quick observing.

I ended up my session on the 24" with a look at Comet Hartley, which I hadn't seen since earlier in the fall.  It was fairly low in the sky, but it was definitely there (see glow to left of center).  I was pleased that 2sky got its position correct.

I then went to the observing field to pick up my Coulter 8" which I had put out in the field at the beginning of the night.  There was ice on the tube, but the scope worked great (except for a problem with the red dot finder that I need to fix).  I had a quick look at M33.  I couldn't see the spiral arms, but I did see hints of detail, and it was quite large.  And then I looked at M42 and it had lovely color: greenish-blue near the Trapezium, moving to reddish-pink in the wings.

Tuesday, December 21, 2010

Lunar eclipse

I stayed up to watch the lunar eclipse.  It was quite nice.  I took the kids out for the grand finale.

I also took a whole bunch of photos.  I'll be editing them a bit more and trying to write some script to align the frames better (and maybe even de-rotating?), but for now, here is the set.  The animation jumpy because I wasn't taking pictures all the time--some of the time I was indoors watching Starship Exeter.  I used a perl script and ImageMagick to animate the photos, using the exif time stamps and speeding up by a factor of 400.  Some of the shadows are odd--I've had trouble with shadows of clouds, branches and internal telescope structures.  I'll eventually try to clean up the photos and remove the bad ones.


Sunday, December 19, 2010

Red backlight keys on phone

Update: Today, I found two of the keys not working.  Peeling back the white plastic showed that there was reddish junk in the dome switch contacts.  I think I must have used slightly too much glue, and it flowed down with melted Rubylith.  Or else the marker ink flowed down.  I cleaned that up with acetone.  But this is something to beware of.  Moreover, some white light spills around the sides of the Rubylith.

My Treo 700P has keys that light up.  One can turn that off, but then it's a nuisance to type things in.  So I ordered a piece of Rubylith from ebay, about 8x11 in size.  The lights come from little white LEDs on the same board that the dome switches are on.  And I reddened the lights, as can be kind of seen in the photo.

Here's what I did.  I disassembled the Treo (not my first time).  My initial thought was to just put a piece Rubylith over where all the lights were, but that would cover up the dome switches as well and that wouldn't be good.  My next thought was just to use red marker over the white LEDs.  But that isn't very effective.  Finally, I cut strips of Rubylith about 1.5mm wide, and snipped them into lengths of about 5mm, and glued them over the LEDs.  The photo on the right shows about half of them done.

I did the gluing with Super Glue (I like the cheap GTC brand [or off-brand] tubes they sell at HEB and Walmart, four for about a dollar).  I held each Rubylith strip with tweezers, very carefully by the very tip, and put a very small amount of super glue on the strip, being careful not to get it on the tweezers.  I then applied it to the LED, pressing it down with a toothpick, orienting it so it wouldn't get in the way of the dome switches.  They didn't all stick as "super" as I hoped, perhaps because of the red marker, but eventually I got them all on.

I had to do two cleanup things.  Two of the Rubylith pieces protruded close to a dome switch (bumps in the white plastic in the photos), and I snipped the ends with nail scissors.  Also, I had accidentally dropped a Rubylith piece with glue on it, and so there was a glue spot on a dome switch.  I was afraid this would harden, so I cleaned it up with acetone.

It all works.  For some reason, the center of the five-way switch is not as clicky as it was, but it works.  Also, the lights are a bit pinkish rather than deep red, but I am pretty happy.  I rarely use a phone at a dark site, but sometimes I need to.

I was also going to make a screen overlay from the Rubylith, and I may still do that, but it blurs the image annoyingly, making small fonts hard to reed.  I may eventually get a sheet of Roscolux medium red gel filter (I tried the small one in my sampler pack, and while it perhaps isn't quite dark enough, and is more fragile than the Rubylith, it preserves sharpness much better).

Wednesday, December 8, 2010

Red trunk lights on the cheap

I've been embarrassed at star parties by the bright white light trunk light in our Taurus. I've finally done something about it, in my usual cheap way. I made a red LED light. I drilled four holes in a 40mm long 3/8" thick wooden dowel. I stuck three mini red LEDs into the holes, with neighboring LED leads going into the same hole. The last hole on one side also got a lead from a 330 ohm resistor (the values will differ depending on your LED specs and battery voltage). I twisted the leads together for better connections, cut them shorter as needed, taped it all up with electrical tape (OK, I've left out some missteps), and popped it in in place of the trunk's tubular incandescent 12V bulb, in such a way that the unconnected LED lead on one side and the unconnected resistor lead, made contact with the metal contacts. Works just fine. Rather dim in daytime, and I haven't tried it at night time. The old bulb drew 0.7A. The new LED system draws much, much less. So no danger of running out the car battery if I leave it on overnight.

I still need to do this to the dome light. My reading of Texas law suggests that alas I am not allowed to do this for the puddle lights ("running board courtesy lights" must be amber or white--maybe this only applies if they're on while the car is going, but why take risks?), so when I go observing, I'll just put some tape over them.

The cost for the whole project was low.  I had the 330 ohm resistors lying around for years (I think they're 1/4W;  ideally, I should have used 390 ohm).  I got the LEDs for about two cents a piece from Tayda Electronics.

There was one unexpected cost.  I blew a fuse when removing the original bulb.  Lesson: Keep the fuse disconnected when doing this, except when measuring stuff.

Monday, November 29, 2010

Amateur astronomy information from 1894

This is really neat. I really like the descriptions of what can be seen with what size of telescope.

Sunday, November 28, 2010

open 2sky release

2sky is a full-featured planetarium application for PalmOS devices. It should work on both the newest PalmOS devices (TX, Centro, Treo) as well as older devices as far back as PalmOS 3.1 and maybe even 2.0. Open 2sky supports standard square screens, as well as the extended non-square screens of just about all devices.

Thanks to Kevin S. Polk's generosity in releasing 2sky to me under the GPL, I am happy to announce that 2sky for PalmOS is now officially released, free of charge. Click on "Download" at:
open2sky.sf.net.

I think the interface of 2sky is a model of elegance. The features include:

  • star catalogs up to magnitude 11 (and smaller catalogs for devices with more limited memory)
  • NGC/IC catalog
  • Solar System objects including Sun, moon, planets, Pluto, moons of Jupiter, major asteroids, bright comets, and meteor shower radiants

This release of open 2sky is essentially the same as the last paid release of 2sky (3.0.2), except that I've:

  • updated US/Canada/Mexico daylight savings rules which had changed in the meanwhile
  • refreshed the asteroid and comet databases
  • added support for Handera and Dana Alphasmart non-standard screen sizes
  • removed the white border around the screen on the TX and some other newer devices
  • rewritten code that wasn't GPL-compatible and made the code-base compile with prc-tools rather than Codewarrior
  • added Waco and Turner Research Station to the locations :-)


The resulting binaries are actually slightly smaller than the last paid release.

Wednesday, November 24, 2010

open 2sky alpha test

After a number of hours of converting code from CodeWarrior to prc-tools and rewriting GPL-incompatible code, I have an alpha test release of open 2sky. USE AT YOUR OWN RISK and please send me or post any bug reports.

http://open2sky.sourceforge.net/

The database building tools are not yet running (actually, Kevin hasn't sent them all to me yet). The Comets and Asteroids databases thus are out of date. However, all of the star databases, up to magnitude 11 are included.

Note 1: The app by default reassigns all the four hardware keys when it runs. This is a problem on devices like newer Treos which need one of the keys for the home button. So, when you first run 2sky on such devices, just unassign your home button when you get to the screen for assigning buttons (to unassign it, tap on the icon for it, and then choose a blank square).

Note 2: I haven't succeeded in running this under a PalmOS 3.0 emulator (dragging doesn't work, and that's crucial), but I have succeeded in running it under a PalmOS 3.3 emulator. Open 2sky works best under PalmOS 5.x. It should support Palm, Tapwave, Garmin and Sony non-square screen devices. It may support Handera ones. The next release will support Dana Alphasmart.

Monday, November 22, 2010

2sky

Kevin S. Polk, the author of the excellent but now alas defunct 2sky for PalmOS, has agreed to have me release it freely under the GPL.  I will be working on converting the code to prc-tools, as well as replacing the GPL-incompatible CollapseUtils-derived code with PalmResize.

Isn't the screenshot beautiful?

Wednesday, November 17, 2010

Clavius

I was playing with my 5mm ortho eyepiece on my 13" last night, looking at the moon and Jupiter, but the seeing wasn't good enough.  But I did take a picture of Clavius with my Canon G7 through my Hyperion 13mm.  Not as sharp as I'd like.

Friday, November 12, 2010

In praise of hard fiber washers

I got a pack of a hundred 3/8" ID 1" OD hard fiber washers from Amazon's Industrial and Scientific sale on sale for under a dollar as an experiment (the regular price is about $16).  A significant portion of my do it yourself budget seems to be washers, so I thought it was worth trying these.  They're great.  The ones I got are black and not glossy so they're suitable for use inside a telescope without painting.  They are a bit thicker than steel washers and a bit thinner than nylon.  They are super-hard, lighter than steel and of course don't corrode.  I know this post sounds like an ad, and to alleviate that impression, I'm not linking.  But search for "fiber washer" in the Industrial and Scientific store, and sort by price from low to high.

Thursday, November 11, 2010

Home-made fine-tuning rings for Hyperion eyepieces

The Baader Hyperion eyepieces accept fine-tuning rings which increase the magnification.  One unscrews the lens group at the bottom, screws in one or more fine-tuning rings, and screws the lens group onto that.  One can buy the fine-tuning rings, of course, for a modest price.  But cheap as I am, I decided to save.  Instead, I purchased two bunches of 48mm camera filters on ebay.  The latest bunch was a lot of ten Niko skylight filters for $13 shipped.  One then removes the glass from the filters, and screws the filter housings into a tube.  The tube is very rigid.  (Removing the glass destructively is easy.  Put filter in some thick bag, hit with hammer or screwdriver or handle of butter knife through the bag.  If the glass breaks, it is easily removed from the housing, though of course one should wear some kind of safety gloves and be careful not to let the glass out of the bag.  Eye protection and a breathing mask are a good idea.  Surprisingly, a number of the Nikos had the glass survive the procedure.)

The ten Nikos add up to 43mm total, and the three Gemkos I have from an earlier purchase give me 14mm.  I could control the length of the fine-tuning tube in increments of about 4.5mm by adding and subtracting one filter housing at a time.

For a total extra price of about $20, my single 13mm Hyperion varies in increments of under a millimeter of focal length between 13mm and about 7.5mm.  The views are really good, though the focus has to be close in with all 57mm of rings attached.  The apparent field of view increases very significantly, which is nice (at full extension, I need to press the eye into the eyeguard to see the whole field of view).  I guess this is because the field stop doesn't increase.  The eyepiece becomes absurdly long, and maybe some focusers won't be happy with the added torque.  I suppose for added fun, I could put in a Barlow, but then the magnification would be more than I can really use.

Friday, November 5, 2010

Astronomy gear and microscopy

I wanted to show the kids the grooves on a CD.  With the medium magnification objective on our microscope, one could just see shimmering graininess.  And I couldn't get the highest magnification objective to focus in on the graininess.  I think the problem may have been that the condenser light couldn't go through the CD, and so I was lighting it with a hand-held flashlight, and that objective has to go so close to the object that blocked the light.  So I got out my 6mm TMB/BO planetary eyepiece (equivalent to about 40X as a microscope eyepiece), popped it in a 1.25" - microscope adapter, and went back to the medium magnification eyepiece, and while we couldn't see it too well, it was obvious that there were pits, and that they were arranged in a line-by-line pattern.

That "1.25" - microscope adapter" is home-made, of course. I cut a 1" segment of 1.25" poplar dowel. I then drilled out the inner 1" of it with a Forstner bit, making a wooden tube with 1/8" walls. I cut a 1.5" segment of some 1.25" ID aluminum tubing (well, actually, a little less than 1.25" ID--I had to sand it out). I then nested the two, with the wooden tube sticking out of the bottom of the aluminum tube, and the aluminum tube extending on top about 1/2" past the top of the wooden tube. (See diagram: gray is aluminum and brown is wood.) They fit snugly, but I put in a couple of drops of CA glue for safety.

The whole assembly then fits around the focuser tube of the microscope, with the top of the wooden tube being flush with the top of the microscope's focuser tube. Eyepieces then fit in the aluminum collar that sticks out on top. The nice thing about making the adapter fit around the focuser tube instead of the more obvious inside is that it doesn't contribute any vignetting.

Of course, it would have looked a bit neater to make the inner tube of aluminum. But ordering an aluminum tube would cost about $8, while a dowel cost $4, plus I wanted the dowel for another project. Moreover, there is an advantage to using a wood inner tube--it won't scratch the outside of the microscope focuser tube as much as metal would. I suppose PVC could have worked as well, but the closest I could find in PVC was 1.29" OD, and I didn't relish the thought of sanding that down to 1.25" OD to fit inside the aluminum tube.

Wednesday, October 13, 2010

Wood Handbook

This looks like a really useful resource on wood.

Sunday, October 10, 2010

Hastings triplets

About two weeks ago, I ordered one of the super-cheap "30X" triplet loupes on ebay for less than $2 shipped (see photo on right). 30X should be 8.3mm (FL = 250mm / magnification, for magnifiers). It came a couple of days ago. To my disappointment, it has turned out to be about 8X (looking on amazon reviews of similar products, this isn't uncommon), i.e., about 31mm. Handheld in my F/4 8" (not the ideal test-bed for this eyepiece!) and pointed at Jupiter it showed significant CA on axis (but it was hard to keep on axis, so I can't swear that the CA was on-axis). I did see one cloud belt, which is about all I can see with that scope. I also tried it on the Double Cluster, and it looked OK, but the AFOV was low.
Today, I used the lens it in a Spenser microscope (just placed it right on top of the eyepiece tube). There it came into its own. I compared it to the Leitz 10X eyepiece (I don't know of what variety) that the microscope came with. The magnification of the triplet was slightly lower. AFOV was about the same, maybe around 30 degrees. Eye-relief was huge (which isn't a plus for me--I like short eye-relief eyepieces). But what was really impressive was the vibrant color and on-axis detail, both significantly better than the Leitz 10X. Despite the magnification being slightly smaller, I could see detail better. The sharpness dropped off significantly in the last 30% of the field.  (Visually, the image was much sharper than in this photo, and the usable area bigger.)
Reading Amazon reviews of similar products led me to the following hypothesis. There are two very-similar loupes being sold out of Asia, both marketed as 30X triplets with 21mm diameter lenses. One variety has "TRIPLET 30X21mm" stamped on it, and it actually is a 30X. The other variety has "30X21mm" stamped on it, and it is close to 10X. It is, nonetheless, a nice piece of glass, but only 10X. (The seller is refunding me my $2.)
Friday night, for $6 shipped, I ordered one of the ones stamped "Triplet" from a US seller whose ebay ads warn against being duped by competitors. The seller avers that his are genuine 30X triplets, and based on an email exchanges with him, I am inclined to trust him (after all, if it's not 30X, he'll have to refund the money, and if he doesn't I'll put in a paypal claim). I should be getting mine in a couple of days, and will report.  I am not posting a link until I've actually tried out the lens.
If that fails, I know a third loupe vendor, out of Canada, who has actually had his optometrist test his 30X Hastings triplets, and found that they are not only 30X, but have AR coatings on one of the surfaces. He sells them for $22.
When it comes, my plan is to bore out a 1.25" dowel and stick the 30X lens in. If it works out, I might even sell a few super-homemade (and not filter-threaded) hardwood triplet eyepieces for some very low price. Or at least give them away to friends. :-)

Saturday, October 9, 2010

Public star party idea

Something I've found to work well at public star parties is to have a durable telescope, or mounted binoculars, which the kids can themselves point.  Both of my tube dobs are durable and beat up, so I am happy to have the kids play with them.  Kids very quickly get the hang of pointing them with the red dot pointers I have on them.

Friday, October 8, 2010

Live Oak School Star Party -- perfect skies

The Live Oak School Star Party at the Waco Wetlands is all set for tonight, but do note that it is at the Waco Wetlands, not Reynolds Creek Park (see previous post for Wetlands directions).  Weather is perfect--no clouds within hundreds of miles of central Texas according to the weather map.

Wednesday, October 6, 2010

Live Oak School Star Party - same time, new place

Due to a mechanical problem at Reynolds Creek Park, we've had to move the Live Oak School Star Party to the Waco Wetlands.  Same time: Friday at 7:30 pm (come earlier if you're bringing a telescope).  This will be a bit of a longer drive, but the skies will be darker so we have a better chance at seeing Comet Hartley.  (And the facilities are nicer, too.)

Location: Waco Wetlands
Time: 7:30 pm on Friday, October 8, 2010
Directions: From Interstate 35 take the Exit 330 and proceed west (toward Meridian) on Hwy. 6/Loop 340. Continue for approximately ten miles to the intersection of Hwy 6 & FM 185. Turn right onto FM 185 and continue 0.6 miles then turn left on Eichelberger Crossing Road. The Lake Waco Wetlands Research and Education Center will be 1.6 miles on your right at 1752 Eichelberger Crossing Road.
Map: http://www.lakewacowetlands.com/map.html

Wednesday, September 29, 2010

Comet Hartley 103P

Finally I had a decent view of it.  Took a long time to find, partly because I didn't realize it was moving fairly quickly, so an ephemeris even 20 minutes out of date had a visibly off position.  What I could see with my 8" at around 68X and 150X was a diffuse oval glow, about a minute of arc in diameter.  The center of the glow was about a minute of arc away from the predicted position, which also threw me off.

Thursday, September 23, 2010

Project updates

I'm at various stages of four astronomy DIY projects.  Projects 2 and 3 are linked in that the eyepiece will have narrow usable field of view, and hence will benefit from the equatorial table.

1. Digital setting circles: I bought a bluetooth-based module that can communicate with encoders.  Unfortunately, I can't get the magnetic encoder to work with it.  I think an oscilloscope might be needed to figure it out.  So I may just need to save up for two optical encoders (360 cpr, and then attached via a 1:4 timing pulley setup).

2. Equatorial table: I had routed the sectors, but it turns out that I had miscalculated the center of mass of the telescope, so the cut radii weren't good.  I've been procrastinating recutting them.  Need to get back to that.

3. Hastings triplet eyepiece: Today I ordered a super-cheap (about $1.80 shipped) ebay 30X triplet loupe.  I think it should be a 8.3mm Hastings triplet.  If it works, I hope to drill out a 1.25" wood dowel and mount it inside as a nice planetary 8.3mm eyepiece.  If it works really well, I might try to sell them for $15-20 each.

4. Laser collimator: This is for a friend.  I still need to print and cut out a collimation target, and then collimate the collimator.

Monday, September 20, 2010

How small stars in the sky are

For optical calculations, it is usual to approximate stars other than the sun as basically point sources of light.  How good an approximation is this?

Well, Alpha Centauri is about four light-years away, and a little bit bigger than the sun.  It is very easily seen, being the fifth brightest star in the sky.  How much apparent space in our naked-eye visual field would the size of Alpha Centauri's disk take up, if we didn't count diffraction, atmospheric effects, etc.?  Answer: Very, very little, about 0.01 seconds of arc.  In fact, it would take up approximately the same amount of space in our naked-eye visual field as an HIV virus seen from one foot away!  The stars take up tiny spaces in the sky.  But they're very bright for their size.

Saturday, September 18, 2010

Easy and cheap small thumbscrew

The set screw on my digital calipers has always been bent, which was a nuisance as it didn't let me tighten them.  I finally got fed up and fixed it.  Turns out that it used an M2.5 screw, and I had a whole bunch of these that I bought to fix our laptop.  But it would be nice to have a knurled head.  Well, I still had a lot of #6-40 nylon socket cap screws that I needed two of for my Daisy finder improvement. So I cut the heads off one of the socket cap screws, and drilled through the hex key hole in the cap.  I then screwed the M2.5 screw into the cap, gluing it place with a package of some cheap no-name super glue that I picked up at a grocery store and that I've been very happy with because somehow it never gets stuck in the nozzle like it does with other brands.  I then decided I wanted a bigger knurled part to turn, so I beheaded another socket cap screw, drilled it, and glued it in place.  Doesn't look perfect, but works great.

Binocular mount

I finally made a binocular mount for my faithful Celestron 15x70s.  It's a parallegram mount with five degrees of freedom: (1) the whole thing swivels where it attaches to the tripod, and (2) goes up and down; the binoculars then swivel (3) up and down and (4) left and right, and (6) can rotate a bit side to side.  It sits on a very short tripod as it's designed to be used by seated me and standing children.

Total cost was quite low.  The long dark pieces of wood are pieces of a recalled cherry crib that was being given away for scrap wood on Craigslist.  Most of the rest of the wood is 1/2" Baltic birch leftover from the 6" F/5 made for my friend, for some parts laminated to approximately 1" thickness.  There are a bunch of 1/4-20 carriage bolts and knobs from Amazon's Industrial and Scientific store.  I had some leftover PTFE for the main azimuth bearing, and purchased some cheap PTFE washers from Amazon for a low price (the price has now gone up by an order of magnitude).  The hideous counterweight is a bubble wrap envelope full of sand, duct taped all around.  The first iteration used a brick, but I was worried that a kid might whack someone on the head with it, and so bubble wrapped sand is better.

It was pretty easy to make.  I used a router for some round pieces, like the semicircular binocular attachment, but polygonal pieces cut with a hand saw would have worked just as well.

The azimuth bearing was the most complicated part.  It's basically scaled-down Dobsonian azimuth bearing: there are three PTFE pads inside, which ride on a CD (two out of my three Dobsonians ride on vinyl records).  This then bolts to tripod platform.

The tripod is entirely home made, too.  I once ended up buying twelve feet of 1.25" PVC conduit at Home Depot or Lowes because I needed a few inches worth for a focuser.  I expected I would eventually find a use for it, and hereby I did.  The tripod platform is a round piece of 1/2" Baltic birch, with some square poplar rods glued underneath, between which the PVC legs sit, attached with a carriage bolt.  To keep the legs from sliding apart too much, I glued three pieces of webbing, I think scrapped from a car seat or feeding seat, glued to the legs with Shoe Goo, and then screwed into place for additional safety.

I may later make a post with more detailed photos, but it was all fairly simple.  One thing that took me a bit of time to figure out is the brown block of wood that the semicircular binocular attachment attaches to.  It is a rectangle of cherry, with an up-down 1/4" hole and an across 1/4" hole.  The latter hole has a permanently mounted carriage bolt.  I used a 5/8" Fortsner bit to dig a deep well for the head of that bolt so that the up-down bolt would be able to sit to the left of that head.  I then filled the well with JB Weld for strength.

Thursday, September 16, 2010

Solar system evening

I pulled out my 8" Coulter, and spent a long time looking at Jupiter, trying different Rosco gel filters.  I think I had my most detailed views of Jupiter ever--it really looked good.  I found the emerald-green and sky blue filters the most helpful.  I then spent about half an hour trying to find Comet 103P/Hartley 2.  It was tough, because in my backyard there are only small patches of sky showing, and in that direction is a lit up street, so I had a hard time identifying a star that I could star-hop from.  Finally, I went for Zeta Cephei, which was 15 degrees away.  I then went field of view by field of view, matching the view through the eyepiece with the chart in AstroInfo.  I found the stars where the comet was supposed to be.  And then I experimented with different eyepieces.  I kept on getting glimpses of something in the area with averted vision.  And once or twice with an O-III filter, also with averted vision.  I was using magnifications between 65 and 150X.  So I guess I saw it.

I rounded out the evening with a look at the moon, another quick look at Jupiter (not as good as earlier) and then a look at Uranus.

Saturday, September 4, 2010

Altitude brake

My Dobsonians move very smoothly.  The problem with that is that if I am showing things to the public, it is easy for people to push the scope away from the object, especially in altitude.  Before the last public star party, I made a little altitude brake, based on ideas on Cloudy Nights.  I used the router to cut a plywood disc the size of the altitude bearings (7" diameter) on my 13" scope.  (Actually, one could just cut a triangular piece with a hand saw.)  A plywood strip (with a plywood pad on the other end) is glued to it as a handle.  I attached three grippy rubber pads (one could put silicone sealant pads, too) near the circumference.  A bolt keeps the handle immobile, and a big 1/4"-20 carriage bolt runs from the inside of the mirror box, through the altitude bearing, through the disc, and then there is a fender washer and a knob to adjust tension.  The handle is bolted to the rocker box.  At low tension, movement is slowed down, but still smooth, despite the grippy pads.  At full tension, movement is stopped.  The original design I was following used a spring, but that doesn't seem to do anything.



I also made a smaller 2.5" version with Velcro hook pads just to slow down, but not stop, movement.  I didn't try it in the field, though.

Daisy red dot finder modifications

The Daisy red dot sight (the best price I've seen was about $8 at Walmart, but last I checked, my local stores didn't have it) makes a decent non-magnifying finder for telescopes. I have them on two of my reflectors, and the third reflector has the Galileo version.  Mounting requires a dovetail.  One option is to take a piece of wood of the right thickness, and then file a roughly shaped dovetail.  Another option is to take a piece of wood, and screw on washers of the right size for the dovetail to fit around.  It's a good idea to mount it offset from the scope for comfort.

A few modifications make the Daisy finders nicer to use.

1. Resistor.  The stock sight is designed for shooting in daylight, so the red dot is too bright for night use.  You can solder in a resistor (I think probably 2K-5K ohm, depending on taste), or you can fold a resistor in half, put a piece of paper between the leads, and put this resistor sandwich between the battery and a contact.  Even better, you can buy a 5K or 10K ohm trimmer pot (e.g., at Radio Shack), drill holes for the leads, and solder wires in place.  Then you can adjust brightness.  The photo shows the version with the pot.

2. Altitude/azimuth adjustment.  The stock sight needs a screwdriver for adjustment.  Since the sight needs to be adjusted from time to time (or even every time, as on my 13" split-tube scope), and using a screwdriver in the dark is no fun, it would be nice to have tool-free alignment.

On the Daisy that's on my 13", the azimuth adjustment screw has a hex nut (attached with some thread locker, I assume) that can be easily turned by hand.  Only the altitude is an issue.  What I did for the altitude adjustment is I removed the screw and turned it upside down so the hex nut is on top.  That nut wasn't big enough to turn with comfort, so I used Super Glue (or some other cyanoacrylate glue) to glue a larger hex nut on top of it.  Works just fine by hand.

The Daisy on my 8" is an older model with round (!) nuts.  The adjustment screws are #6-40, a bit less than an inch in length.  Amazon's Industrial and Scientific store had a really cheap pack of 100 black nylon socket cap screws (about 50 cents), so I got that.  I was a bit worried if nylon screws would work well.  But they did.  The azimuth adjustment was straightforward: I just replaced the stock screw with the nylon socket cap screw, and the knurled head of the screw nicely turns by hand.  The altitude adjustment was moving poorly with the first screw I put in.  I removed it, and put in another, and it was fine.  Maybe there was something wrong with the thread in the sight, or maybe the screw wasn't good.  But, hey, I had 98 others at that point.  Looks good, too.

Finally, I trimmed the screws right outside the nuts by cutting them with kitchen scissors.  That also spread out the ends of the plastic screws, which should keep the nuts from coming off them.  But for good measure, I took a soldering iron and squashed the part sticking out of the nut, so the nut wouldn't spin off.  (If I need to exchange screws, I can always trim with box cutters.)  I went for nylon screws in the first place because they were so cheap, but in this application, they're also easier to work with (no need for any thread locker or hacksaw), and they won't rust.

The only issue is that (as of Sept. 4, 2010) the price on the screws has gone up to about $6.  Fortunately, they still have a pack of 50 of white versions of these screws for 82 cents.  If you have Amazon prime, or are doing a $25 order, the shipping will be free.  (If you can't get free shipping, you can paypal me the price of a stamp and if I still have enough, and there aren't too many requests, I can send you two of the black ones.  And maybe even a resistor if you want.)

3. Removing coating.  The stock sight comes with a lens that's coated with a dark reflective coating.  The sight is still usable, but you can't see dimmer stars through the lens.  That's not a big problem as you can keep both eyes open and see the stars with the other eye, but stripping out the coating is a nice idea.  This was hard work--about an hour for each sight I did this to.  And one of my sights now points differently from before--I don't know why.  To get it aligned with the scope, I had to angle the dovetail mount on the scope quite a bit.  The image also isn't as neat a dot (and some have seen ghost images).  All in all, I still think it's an improvement, though just barely worth it given the work.

The first step was to remove the lens--I can't remember if there was more than one.  There is a plastic retaining ring holding the lens in place.  Remove that first.  I did it by use of a jeweler's screwdriver, wedging it in behind it.  Once when I did it the ring got creased--it's not so strong--but it was still fine.  Be careful that the lens not fall out, as you will need to note the direction the lens is pointing.  Then remove the lens assembly.  Make careful note of the direction in which the lens is pointing--one side is coated, and the curvature is only on one side.  If there is more than one lens, do it for all of them.

Now, it's time for the hard work of polishing off the coating.  I don't have a satisfactory method.  I used two different polishing compounds: toothpaste plus water, and baking soda plus water.  Generally, I first did the toothpaste, and then moved on to the baking soda.  I applied them with denim.  I did this by hand, which was slow and inefficient.  The other thing I tried was to wrap the cloth with polishing compound around the handle of a screwdriver, duct tape it into place, load the screwdriver blade into a drill, and run the drill.  Eventually, you notice that the coating in the middle is disappearing.  It's really frustrating to get every spot off near the edge.  Some you may just want to live with.  Once done, wash, dry and put back in.

Tuesday, August 31, 2010

Cheap hardware

I've lately noticed that Small Parts has discounted a lot of their inventory in Amazon's Industrial and Scientific store. As long as one gets free shipping with a $25 order or with Amazon Prime, the prices are lower than at my local hardware stores (and if one counts the gas, much lower). For instance, I needed two 1/4-20 knobs for a tailgate. Small Parts had a pack of five nice three-lobe female 1/4-20 knobs for about $1 (one can browse all their knobs by searching for "1/4-20" dimcogray). I needed three #6-32 collimation screws for a laser collimator. I got five really nice mil-spec stainless steel screws for a total of 30 cents (their mil-spec inventory seems really highly discounted)--my local hardware store has zinc plated #6-32s for about 12 cents each. Yesterday I needed two socket cap #6-40 screws for one of my Daisy RDFs, so I could adjust them by hand. A pack of fifty nylon socket cap screws was about fifty cents. (I am guessing that at Lowes they would have tried to sell them for about $0.75 for two, and I'd have to pay for gas.) I also bought two timing belts and timing belt pulleys for a $1.63--I'd have paid about $10 plus shipping at SDP-SI.
A lot of these items are marked as heavily discounted, by up to 90%, so I don't know how long this will last. They can't be making money on a lot of these. It's weird to shop online for items under 50 cents.
My currently going projects are: (a) digital setting circles for my 13" and (b) equatorial platform for the 13" (that's what the pulleys are for). I think I will also make a parallelogram mount for my binoculars.

Sunday, August 22, 2010

Hectospec M31 catalog for AstroInfo

If anybody other that me is using the free AstroInfo for PalmOS, I've uploaded a catalog of objects up to mag 16.5 in M31.  The catalog is based on the one on this great site, which is worth visiting whether you have a Palm PDA or not.

Sunday, August 15, 2010

Chalkboard paint

I painted the inside of my 13" Coulter Dobsonian with Rust-Oleum latex brush-on chalkboard paint ($10 at HomeDepot;  the two coats I applied used up about a quarter of the 30 ounce can), because I heard that chalkboard paint produces a nice and flat finish.  By and large, it did.  In some areas it wasn't quite as flat as ideally, but those were rougher areas, so the light will be scattered there anyway.  It's the flat and smooth areas that are most important.

I will let it try for a while before putting the optics in, and then there'll be lots of moon out, so it'll be a while before I can seriously try it out.

Friday, August 13, 2010

Perseids

I've never had much luck with meteor showers.  It's always been either cloudy and I wouldn't go out, or else I couldn't see anything (I've seen the occasional meteor on other occasions).  But last night I took my kids out to my dark site outside of town.  It was promising that as we were driving down, my daughter saw one out the car window.  On location, she saw two more, and I saw two (maybe not the same ones).  They were nice and bright.  Unfortunately, my 5-year-old son didn't see any, and he cried about that.  But I showed him the Milky Way and that comforted him.

I had sent out an email to my club that I was going, and when I arrived there was already a couple there, in conversation with a suspicious police officer who was wondering what we were going to be doing, how many people were going to be there, and how long we would be.  He also id'ed them.  As soon as I arrived, he seemed to get much less suspicious, and after a question or two, he drove away.  But he kept his car about 1/3 of a mile away with headlights on, I think to keep an eye on what we were up to.

I took my 8" Coulter along, and we also looked at M8, M13, M20, M22, M57, a bit f the Veil, and the Owl/ET/Airplane Cluster (which I've noticed always pleases people).  I couldn't find M81/82, because it was low in the sky, and in Waco skyglow, and there weren't enough naked-eye stars in the vicinity to quickly star-hop to it (I could have done it slowly field-by-field, but not with the kids and the two other people waiting).  Not having used my 8" Coulter much for deep sky stuff recently, I had forgotten that it is a rather nice scope.  I appreciated the crispness of its F/4.5 optics--better than my F/4 travel scope with its cracked and scratched mirror.  And I am quite happy with the helical Crayford focuser, though I need to put in some star nuts to make sure the bearings don't rotate out of the way.

Wednesday, August 4, 2010

My 8" F/4 travel scope: Traveling

I visited my parents in BC, Canada, and finally got to do air travel with my travel telescope, which is what it was designed for.  The eight pound mirror box was in my backpack.  The rest of the scope (another 8.5 pounds) was in my suitcase, as were my eyepieces.  It made it just fine.  On the way out, I had to open the mirror box cover up for TSA.  They asked about a blackish stain on the mirror box, which I said was either paint or a table saw burn (closer examination later revealed that it was the latter).  No questions were asked on the return.

The eyepieces were packed mostly in bolt cases, and then in bubble envelopes, and a soft bag that was inside my and my son's big suitcase.  There was also my home-made laser, which I put in a cardboard box that I labeled "telescope collimation laser" because I knew it might puzzle TSA.  In both directions, the suitcases ended up with a card from TSA saying they had opened it.  They kind of messed it up on the return leg, not zipping up the inner bag with the eyepieces, and putting the lightshield randomly in the middle of the suitcase, rather than tucked in by the bearings to prevent damage.  But no damage was done to anything.

The scope did very well on Saturna Island.  I used to think it was no good for planetary purposes, but one night it actually did decently on Jupiter and the moon at 200X (TMB/BO 6mm + Barlow cell).  I had hoped for darker skies, and I thought that with the moon rising at around 10:30 pm, I'd get some dark sky time before moonrise, but I forgot that up north in the summer it only gets dark really late--like 10:45 pm.  Moreover, with the moon rising over the sea, even when the moon was very low, it was not covered by anything.  Nonetheless, my parents and sister liked the E.T. / Owl Cluster, and several other deep sky objects, and both Jupiter and the moon were hits.  Maybe next time I visit, I will do a public star night.

I also got to see some nice killer whales through the scope.  The scope works quite well for terrestrial purposes at 27X (30mm Rini)--the whales were quite some distance away, but they were very clear.  And the mount is nicely solid for daytime use, and one doesn't need to worry about objects slipping from the field of view.

I did find that with my 13mm Hyperion, the balance was off for elevations below about 30 degrees, even with the springs attached.  For low elevation work, I ended up hanging a small drawstring bag with about one to pounds worth of stuff inside.  I hung it from the wingnuts holding the strut to the mirror box.  I like this way of doing a counterweight--I can just travel with a drawstring bag, and then fill it at the destination with whatever heavy objects (rocks, other eyepieces, whatever) I can find, and the counterweight doesn't add to the travel weight.

Saturday, July 24, 2010

Eyepiece case


I've found it a nuisance to take eyepieces in and out of bolt cases.  Moreover, the amount of time it takes to pack up everything at the end of an observing session limits the length of the session.  So I decided to make one of those eyepiece cases where the eyepieces sit naked and can be used right out of the box.  I initially planned to make a plywood box, but decided that would be too heavy.  Instead, I picked up a Harbor Freight steel and plastic toolcase (like this one, but maybe slightly smaller) for a low price, and made a plywood insert.  Unfortunately, the case was stinky.  The plastics in it were off-gassing.  It took about seven weeks of ventilation until it became usable (obviously, I don't want off-gassing onto optics).  Finally, today, I put the insert in--gluing it in place with silicone glue and putting some screws in.

It includes space for 1.25" and 2" eyepieces (the laser collimator occupies one of the 1.25" slots).  In the middle there is room for filters.  I drilled two holes through all my slide-mounted Rosco gel filters, and put machine screws pointing upwards on the insert for the filters to sit on.  The fit is good.  My ND and OIII filters are in a plastic box attached with Velcro (or maybe a generic hook and loop fastener) to the insert.  Finally, on the right side, there is room for my battery box (for driving fans or giving extra power to PDA), geen laser, flashlights and spare batteries.  I am quite pleased.  But since the silicone is still off-gassing, I took everything out after taking the photo.

Sunday, July 18, 2010

Fun in less dark skies

Last night, I went out to my usual just outside of Waco site.  Not as dark as the observatory in Clifton, and not only was the moon out, but there was a fair amount of traffic.  But I had my 13" which compensated to some degree.

The moon looked OK at 500X and better at 375X.  Venus showed its phase, but that was all.  With the exception of the Splinter Galaxy (NGC 5907) which I hadn't seen before but which happened to be on the Best of NGC/IC list I was using and with a high altitude, I was looking at Milky Way objects.  M57 looked rather nice--no central star (never seen that), but a nice eye shape, not just round.  M13 looked decent as did M92 (which was hard to find for some reason;  maybe because AstroInfo wasn't set for the current time).

Most of my time was spent going through objects in Steve Coe's What's Up Sagittarius and Scorpius articles, which I keep plucked on my PDA (with permission;  I even have it set up in a cool way so that when I click on an object in the text, it takes me to AstroInfo's search, though this wasn't working always last night).  I did all of the Sagittarius objects (Coe only covered a small portion of each constellation) except B91: M8, M20, M21, Collinder 367, NGC 6544, NGC 6546, NGC 6559.  I thought I had B91, but I had overestimated its size (to remove that problem in the future, I added Barnard's catalog of dark nebulae to AstroInfo).  And then I did a few of the Scorpius ones: M80, M4, NGC 6144.  There was a clear dark lane in M80.  6144 was hard to find.

I ended with a look at the Veil Nebula.

The views in the mediocre conditions in the 13" were similar to those in the 8" in the better conditions of my previous session, though M13 was better resolved.

Focuser tube baffling

I've been having bad light control problems with my 13mm Hyperion eyepiece in my 13".  Whenever there is anything even slightly bright opposite the focuser--even if it's just skyglow at a pretty dark site--it was flooding the field of view.  So I made a simple focuser baffle.  I just cut a cardboard ring with inner diameter just over 1.5" and outer diameter 2.2".  The inner diameter was arrived at by ray-tracing.  The outer diameter fits the focuser tube.  I then just slip it into the inner edge of the focuser tube.  Because the focuser tube inside is threaded (or just ringed) it stays in.  I also added a wide ring around the outside of the focuser tube, inside the scope's OTA, but I don't think this was what made the difference.

Result: Great!  Last night, I was able to observe with the 13mm despite the moon, a family fishing with a light hanging over their stuff, and boats in the water.

I also have a large foam light-shield, which I occasionally used, but the baffle ring seems to render it unnecessary.

I expected the baffle to vignette the field of view of my 30mm Super-View, but I left it in for convenience even when I was using that eyepiece, and the views were fine.

Tuesday, July 13, 2010

Quick but fun dark sky session

I went to the Meyer Observatory last night to learn a bit about the operation of the 24-inch telescope.  Unfortunately, the camera shutter wasn't working.  While it was being fixed, I sneaked out and pulled out my 8" F/4 telescope, which I brought along.  I had a rather nice and very fast session under really dark skies--about 20-25 minutes.  Actually, my first impression of the skies was that it was cloudy and the clouds were lit up by city lights.  In particular, Sagittarius looked really clouded over.  What an embarrassing mistake!  The clouds were clouds of stars--the Milky Way!  Unfortunately, I forgot to bring my 30mm 1.25" eyepiece, and the scope only has a 1.25" focuser, so I was stuck with a 13mm, which rather took away the scope's wide-field advantages.

I started with M13, which resolved fairly well, but not as well as in my 13" from brighter sites, though I had a hard time finding Hercules--too many stars in the sky!  I had a nice look at M51.  It had its companion visible, and there definitely was a connection between them.  I got a vague hint of spiralness.

M57 was a nice little donut.  Better than I expected from this very fast scope with a damaged mirror.  I then tried to find M20 and M8.  While trying to point to M20, I hit M8, which was very nice.  In fact, M8 was naked-eye, with a nice dark lane down the middle.  M20 was a little ways up.  I don't think I saw all of its three dark lanes, but I did get an impression of at least two.  I tried for the American Nebula at some point, with no luck, because the field of view was too small.  And I also tried for the Veil Nebula, and did in fact get a nice line, which may have been the broomstick, but it was hard to tell--the image wasn't as sharp as when I used my 13".

Still, it was a very nice session squeezed in a short amount of time.  I rather like a scope that weighs less than 17lbs.  I am looking forward to taking the travel scope by plane to Canada.

Saturday, July 10, 2010

Fun with meteorite and magnets

About two years ago, I got a free L6 meteorite sample from Inner Planetary Products (now, alas, apparently defunct).  Here was a fun thing to show my son: one can pick up the meteorite, which looks like a small stone, with a magnet.  The L chondrites are about 4-10% nickel-iron according to Wikipedia.  A fun science project for a kid would be to check how magnetic different meteorites are.  If one could get good-priced samples.

Sunday, July 4, 2010

Cross-hair laser collimator: Part I

I'm making a cross-hair laser collimator for my friend's 6" F/5 scope--actually, the final steps will be done with him.  I've already made one for myself.  Instead of having a laser dot, it has large cross-hairs.  This looks cool, and is in some ways nice to use (e.g., the cross-hairs light up the central donut a bit in the dark, and you can align them more precisely on the return target than a single dot that might disappear inside the target hole), though it's not so good if one prefers a Barlowed laser collimator.  The costs are low.  The laser module itself costs $4.06, including shipping, and most of the cost is a couple of inches of aluminum tubing from Speedy Metals.

The body of the collimator is made of two pieces of T-6061 aluminum tubing, the larger of 1.25" outer and 0.75" inner diameter and the inner of 0.75" outer and 0.5" inner.  This is very hefty and solid aluminum tubing.  I need a 1.25" outer diameter to fit in the telescope focuser.  But the laser module has a 0.4" diameter (approximately, going from memory).  So one needs to bridge the gap, and as I couldn't find laser tubing of 1.25" outer and 0.5" inner diameter (the last 0.1" is bridged with electrical tape, and one needs some wiggle room for adjustment), I had to use two.  Plus, I only want the 0.5" diameter in the last 1.5" of length, so there is more room for the cross-hairs on the return beam.  So nesting the tubing is the trick.  Unfortunately, 0.75" outer diameter doesn't fit in 0.75" inner diameter, as the tubing is not made to tolerances that make telescoping possible.  Moreover, aluminum on aluminum friction is very high--as high as rubber on dry cement.

Hence, one has to sand the larger tubing from the inside and the smaller tubing from the outside.  I ended up sanding the larger tubing from the inside by attaching sandpaper (with duck tape) to the handle of a screwdriver, with some foam in there to add pressure, and spinning the contraption with a hand-drill to sand.  I went through a bunch of sandpaper that way, but finally the small tube started sliding in.  And then it stopped.  Aluminum on aluminum friction is very high.  I hammered it in a bit more, but an inch was left sticking out.  Which is perfectly fine.  There was not going to be any problem with sliding away, because of that amazing coefficient of friction.  Anyway, so I had about an inch in and an inch out.  Also, the outside of the 1.25" tubing needed sanding to fit inside the focuser tube (which was also aluminum, so I was afraid it would get stuck there if there wasn't some wiggle room).

I then cut a 45 degree slice out of the tubing.  A little too close to the end--I should have done it in past where the smaller tubing was.  (As it was, to allow more room for the cross-hairs, I ended up expanding the hole with a Forstner bit.)  I used two pieces of steel bolted around the tubing at 45 degrees as a guide for the hacksaw while cutting.  Took a long time.  Aluminum may be relatively soft, but cutting through such thick tubing at an angle still takes a while.

Next, I drilled three holes for adjustment screws--the collimator needs to be itself collimated.  I then planned to tap it by driving #6 screws into it.  One went in fine.  Another broke as I was screwing it in--it just sheared its shaft.  I managed to remove it.  A third broke off flush with the tubing.  That one was nasty.  With a friend's help, we tried to remove it in various ways.  Finally, a punch made a small hole, we drilled a ways in, and then I just drilled a new hole right through the screw shaft.  My friend also told me that when one uses a screw to tap a hole, one needs to go two partial turns in, and one out, and so on, while I was foolishly screwing straight in.  I tried that, and broke a second screw in that same shaft.  Oops.  Around then I realized I had drilled the holes one size too small, and that's why the screws were breaking.  I sanded it flat again, drilled a slightly larger hole than before, and tapped it successfully.  Whew.

The laser assembly is much easier than the housing.  The laser is a <5mW unit, and I assume is safer than the typical unit as the crosshair grating diffuses the beam quite a bit.  The laser comes with two nice wires.  I attached a switch and a battery pack.  The battery pack was made of three 1.5V LR44 batteries taped together, and some scrap pieces of thin metal for contacts for the wires touching them.  The laser also has a focusing ring.  (If one removes it all the way, one can remove the crosshair grating, and get a laser dot.)  I focused it for roughly the length the beam would have in the scope, namely focal length times two, though it'll probably get defocused before I'm finished and I'll have to do it again.  I used some heat shrink tubing (nice stuff) to make the connections more solid.  And I transferred the warning label from the laser module to the housing.  The batteries and switch will stick out of the back of the collimator.  Not so pretty, but usable and easy.

Steps still left: wrap bottom of laser in electrical tape to fit snugly in housing, insert, add adjustment screws, adjust laser, add a cardboard target, mark cardboard target, and then put in something to keep it from falling into a focuser tube (maybe a little screw? maybe a dab of silicone?).  That'll be another post, and these last steps will be done with my friend.

I should say that I've made one of these for myself, so none of this is breaking new ground for me.

Friday, July 2, 2010

Wooden helical Crayford focuser

I've done this project a while back, but in case anybody is interested, I am documenting it.  My Coulter 8" scope came with a friction focuser made of pipe fittings that Coulter described as "helical", I think because you aren't going to do very well just pushing the focuser tube in and out unless you give it a twist as well.  With practice, the focuser was usable for light eyepieces, but it really didn't work for something as heavy as a Hyperion 13mm (and there are eyepieces heavier than that).  So I decided to make a helical Crayford focuser, because I was too cheap to buy a KineOptics one.

The idea behind a helical Crayford is that you have ball bearings against which the draw tube rotates.  However, the ball bearings are slightly twisted so that their axes make a small angle with the angle of the tube.  Consequently, as you rotate the draw tube, it moves in and out.  If the ball bearing angle is larger, the movement is faster, and if it's smaller, the movement is slower.

I mounted the ball bearings on two T-shaped supports made by taking a #12 flat-head screw for the stem of the T, and JB Weld'ing a segment of 1/4" square rod to the head of the screw for the line.  I then JB Weld'ed a  skateboard ball bearing (I expect from VXB's ebay store) at each end of the T's arm, trying as best I could that everything would be square and the arms of equal length (not that I am very good at that sort of thing).  I then took a piece of 3/8" particle board (Baltic Birch plywood would have been better, but I was being cheap) and mounted three posts on it.  Two of the posts would sport the ball bearings, with the stem of the T going through the post, and with various nuts and spacers to hold the bearings in place.  The third post had a little flap adjustable with a thumbscrew.  The flap was made of a piece of bondable PTFE JB Weld'ed to a piece of metal, with the thumbscrew bearing against the metal, all as in my push-pull Crayford.  For the draw tube, I used the aluminum draw tube from the Coulter.  In the picture, the hole for the focuser tube wasn't cut yet.

Here's another picture, with a better view of the T-shaped ball bearing supports.  You can see the gray JB Weld all over the  place.  Two things to be careful of when gluing are (a) don't get any JB Weld on the bearing surface, because then movement will be bumpy and (b) ensure that the JB Weld stays on the inner ring of the ball bearings, so it doesn't stop the ball bearing from moving!  Note also that the posts are located in such a way that the focuser tube would fit snugly in.  At this point in the process, the posts are, I think, screwed in place.

Eventually, I unscrewed the posts, cut a hole of the focuser with one of my trusty cheap Harbor Freight hole saws, sanded the faux veneer off the particle board, glued the posts with JB Weld to the particle board, with screws for added strength.  Or something like that--I don't remember all the details.  (It's possible that at some point the posts were weakly affixed with craft glue to help with layout and then pushed off.)

I did have one worry, and that was that the posts might bow outward with time, thereby decreasing tension, and generally making the focuser not work too well.  So I JB Weld'ed some strips of hardwood that I had lying around in my scrap pile, joining the posts as if with a fence between fence posts.  I was generous with the JB Weld.

Finally, I cut the particle board down to size, removed the old focuser (cutting the sonotube around it, ripping it out, etc.--it was a messy procedure), and attached the particle board with screws and some hardwood rails to fit to the curvature of the tube.  I also painted the wood and JB Weld black.  It's pretty heavy, but somehow fits the home-made styling of the Coulter scope.

The focuser has had a bit of image shift, which has increased with age.  Lately, it wasn't doing too well, so I had a closer look at it.  It turned out that the T-shaped supports, under pressure, had rotated further, so that the angle between the axis of the ball bearings and the draw tube was too big for good movement.  I made the angle smaller, added washers under the nuts (did I forget? or maybe I just ran out of washers?), and tightened it up.  I am guessing they'll rotate away again.  If they do that, and maybe before that, I may replace the nuts with locknuts, and/or add some toothed washers.

The focuser weight is an issue--I've had to increase the counterweight--but that's part of the price of making stuff out of wood.  And the price is hard to beat: a couple of bucks for the bearings, and then some screws, washers, nuts, square rod, and various pieces of scrap.

Sunday, June 27, 2010

Off-gassing

About three weeks ago, I bought a plastic and steel tool case from Harbor Freight to use as an eyepiece and accessory case.  The price was right, and I made a nice plywood insert with holders for the eyepieces.  But the case turned out to be stinky, no doubt due to the plastic off-gassing.  I can't put optics in it while it's still off-gassing as then they might be coated with the residue.  I've kept the case for most of the three weeks in the garage, open, hoping that the Texas temperatures would help, but the effect has been fairly small.  Yesterday, I went some steps further.  First, I left it out in the sunlight for a couple of hours.  Second, I filled the plastic bottom portion with a mix of water, dish soap and hand sanitizer (didn't have alcohol in another form) and left that in for a while.  Then I poured that out, wiped it, and left it in front of a fan for an hour or two.  It didn't smell much then.  But then after its spending another night in the garage, it's smelly again, but pretty definitely less than before.  Annoying.  But I think once I get all the smell out, I'll have a nice eyepiece case which will cut pack-up time by a few minutes, so I can stay at dark sites for a few minutes longer.

Sunday, June 20, 2010

Back from trip

I've just come back from a conference in Ireland.  I didn't do any stargazing there, but as always it's amazing to see how long the summer days are up north (latitude 53 versus the 31 of my home).  Here's a photo of the moon (left) and Venus (right--to see it you may need to click to blow up the image, or adjust the contrast on your screen) over a foggy golf course in Maynooth (Canon G7 braced on a bridge railing, set to 1600 ISO and 1/10 seconds), at around 9:50 pm local time.

Friday, June 11, 2010

Using three cent Rosco gel filters for planetary observing

As an experiment, I bought the Roscolux Swatchbook from B&H Photo for $2 plus $5 shipping. One can also get them free from a Rosco dealer if one lives near one (Lee also has a version). Anyway, what you get is about 250 gel filters, each 1.75" x 2.75" (with a hole that mounts it in the book) and each with a light-transmission curve. Anyway, one can then hold a filter between eyepiece and eye for planetary observing, assuming sufficient eye-relief (a reason to use long ER eyepieces). The filters are meant for stage lighting, and the small format are sometimes used for coloring a camera flash or strobe. I didn't know if they had the optical quality for actually looking through them, but thought it was worth trying, and so I ordered the set.

I had a bad experience in the past with a basic Celestron color filter set. While they occasionally may have teased something out, they scattered the light too much.

Here are my initial observations of the Rosco filters. The standard Roscolux gel filters look optically good to the naked eye--no obvious irregularities. (There are also included some special filters that are intended to scatter light. Obviously, these are unusable for astronomy purposes.) When I looked through them indoors naked-eye, I saw some light scatter around light bulbs (a small halo), which worried me a bit. (I hadn't done this test with the Celestrons.) But otherwise the image was very sharp.

I then took the set outside with my 8" F/4.5 Coulter, with a 6mm TMB/BO for 150X (I actually should have used a higher magnification, but I was in a bit of a hurry). Targets: Saturn and Mars.

I initially couldn't see any detail on Saturn without a filter. Occasionally, I got an intermittent hint of a band in the north.

I started with red filters. I could barely see Saturn through #27 Medium Red (4% light transmission). #26 Light Red (12%) was better, and occasionally--the seeing must have been quite intermittent--I got hints of a sharply defined Northern band. What worked best, however, was #23 Orange (32%). The band only appeared from time to time, but when it appeared it had a sharply focused appearance. Moreover, the filters removed the annoying CA that my TMB eyepiece contributes. I tried Moss Green (45%) but it did nothing for me.

I then moved on to Mars. Orange helped control the bloom that I get from the 1/8" thick double-vane Coulter spider, and it highlighted a dark feature near the south pole.  The ice cap was visible, too.  I eventually was able to see the feature and the ice cap without the filter, but the view was much better with the filter. Moss Green again did nothing for me.

But the really happy news was that I had none of the blurring that I had with the Celestron filter-thread filters. The rings and their shadow stayed sharp. At three cents per filter, this is a great deal.

Cons:
The filters are very flimsy--I don't know how long they'll last. Moreover, they are hard to use when in the book. I need to find some way of getting them out--simply trying to flip them out of the book doesn't do the job well. Moreover, if I hold the whole book with the filter in front of the eyepiece, the filter wobbles and the object moves, which of course makes it harder to see detail.

Pros:
Sharp images. Very large selection of filters, with a large variety of light transmissivities and for fine-tuning the choices. Includes light a transmission curve for each filter. Super cheap: get about 250 (not all astronomy-usable) for the price of one filter.

Future work:
I want to make a holder for these in my eyepiece case. I am thinking of putting up two steel rods sticking out, one for permanent storage of the filters and the other for the filters I am using during the session. There would be Velcro'ed webbing to keep the permanent storage filters from flopping away.

I also want to experiment with the gel filters as full-aperture filters. One can buy them in 20"x24" sheets for $6.50 plus shipping. In fact, one of the main reasons I got the swatchbook was so I could figure out which colors I wanted in the full-aperture dimensions. Orange is definitely going to be there.

Saturday, June 5, 2010

6" F/5 Dobsonian: Finished (at least my part)

We cut up the 1/2" (actually a little less Baltic Birch) on a friend's table saw (thanks!), and finally glued most of it up yesterday.

There is a hexagonal box around the center of gravity of the telescope tube.  That was hard to do.  I thought I had the table saw set to very close to 30 degrees from vertical (with a precisely cut piece of cardboard) and I thought we were getting 0.01 inch precision on the length of each cut, but the box was a bit too big, and the angles didn't quite close up.  To compensate for the size being too big we cut two sides a bit smaller, and we shimmed between the box and the tube where needed.  Here is the hexagonal box drying, held together with a giant rubber band (red) and Duck tape (silver).

The rocker box, on the other hand, came out really nicely.  The round parts were done with my fixed router.  We did need to use a home-made drum sander (plug cut by hole-saw on a bolt spun by a drill, with sandpaper hotglued--unfortunately, eventually the sand paper came off) to expand the sides.  I also glued 1/16" bondable PTFE pads to the sides under the rockers, and used the rockers themselves to press the pads down.  The clearance is pretty small--we'll see if any problems develop as the wood ages.

The rocker base is very simple: just a round piece of plywood, with three round legs (2.5" plugs from using a hole saw to cut the lightening holes in the rockers), and PTFE pads near the legs (for stability).  Bricks used for clamping both the pads and the legs.

Finally, today, with the kids' help I added the rockers to the tube.  I also added little wooden thingies, with PTFE lining inside the rocker holes on the box to keep the rockers from falling off.

And here is the finished scope.  Well, finished, except for finishing the wood, which is for my friend.  Interestingly, the tube and the primary cell are really stable.  Even though we did all that stuff with the tube, and the primary cell was removed for much of it, when I put the primary cell back in, although secondary collimation was off (I think that single-stalk secondary holder may need an upgrade eventually), primary collimation was almost exactly spot-on.  I also put some silicone on the outside of the inner edge of the focuser tube, where the Crayford focuser's bearings go, so the tube can't be racked too far out.  To prevent it from being racked too far in, the set-screw for eyepieces is located so it'll hit a wooden piece eventually.  To remove the focuser, I guess one either has to twist the focuser tube past the rockers (not good for the aluminum of the tube) or remove the secondary and get it out from the inside with the set-screw removed.  Now my friend has to finish the wood.