Monday, December 27, 2010
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.
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.
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.
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.
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
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
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.
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 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
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
Sunday, November 28, 2010
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:
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
Monday, November 22, 2010
Isn't the screenshot beautiful?
Wednesday, November 17, 2010
Friday, November 12, 2010
Thursday, November 11, 2010
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.
Friday, November 5, 2010
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
Sunday, October 10, 2010
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
Friday, October 8, 2010
Wednesday, October 6, 2010
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.
Wednesday, September 29, 2010
Thursday, September 23, 2010
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
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
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.
Thursday, September 16, 2010
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
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.
A few modifications make the Daisy finders nicer to use.
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.
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.
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
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
Sunday, August 15, 2010
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
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
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
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.
Sunday, July 18, 2010
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.
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
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
Sunday, July 4, 2010
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.
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
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.
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.
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.)
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
Sunday, June 20, 2010
Friday, June 11, 2010
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.
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.
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.
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
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).
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.