Thursday, December 22, 2011

ScreenDim and RootDim (formerly SuperDim) apps for Android

1. I put in the Android Market a new paid screen dimmer, ScreenDim, loosely based on my SuperDim code. ScreenDim allows you to dim your display below what the OS normally allows, does not need root, and does both backlight and contrast adjust (at least on backlit devices). (The contrast adjust function is visually like ScreenFilter functionality, but my testing suggests that ScreenFilter may slow down 2D rendering by 30%, while I haven't observed a significant slowdown with ScreenDim.) You still have profiles. But because this app is aimed at non-root users, I removed ChainFire3D integration as well as extra LED support (I may do something in the latter direction if there is an open API.) It will be interesting to see how ScreenDim does on OLED devices on which SuperDim didn't work. There is a free three day trial version.

2. I renamed SuperDim to RootDim to differentiate it from ScreenDim.

3. I have not abandoned RootDim/SuperDim. I uploaded a new version to the Market that should give better control over LEDs. You can, for instance, set the power LED to turn on when and only when charging, or when the device is on, or never, etc. I think there are still some bugs in this functionality, and the functionality does not turn on automatically after a reboot until the bugs are worked out. But it's a start.

Wednesday, December 21, 2011

SkySafari out in Android Market

SkySafari is now up on Android Market.  I've been one of the beta testers.

Here's my five-star Market review:
This is easily and by far the best astronomy software for Android devices.  I think it's better than Stellarium for the desktop.  Superb coverage of the solar system (planets, minor planets and comets) and deep sky objects.  Good information on various objects.    It's great to have outlines of wide deep sky objects.    The Pro version adds tons of stars.  From my experience with Palm apps, for serious star-hopping and identifying of faint objects with a decently sized telescope (I have a 13"), one really should benefit from having the greater depth of coverage that the Pro version provides over the Plus version.    Hint 1: If you have a somewhat slower device, you can greatly improve smoothness by setting the Horizon to Transparent with Line and turning off Milky Way textures.  Hint 2; While the built-in night mode works well, it doesn't affect the on-screen keyboard keyboard or any soft keys on screen if your device have them.  For rooted devices, you can install ChainFire3D and use its night mode, and for unrooted devices, you might try my own free "GB keyboard with optional night mode".

Monday, December 5, 2011

LunarMap HD and Lite officially released

I finally got to the 1.00 release.  It's now in the Market:
The screenshot shows the Lunar Reconnaissance Orbiter's false-color far-side map (HD version).

And here is the latest Lite apk file.

Sunday, November 27, 2011

Official release of Android keyboard with red night mode theme

Astronomy apps may change most of the screen to red, but they leave the keyboard alone.  If you have a rooted device, you can get ChainFire3D to fix this problem which provides a device-wide red screen mode, but for non-rooted devices, that isn't satisfactory.

To remedy this, there is my Android keyboard with red nightmode theme, now released here.

Wednesday, November 23, 2011

Solar projection

I made a little cardboard solar projection box for my 8" Coulter, and a mask to cover all but 2.9" of aperture.  I read a hint to put two holes in to get the resolution advantages of the aperture--I may try that one day.  Or I might open up more of the aperture and use IR-rejection film, though that may be risky for the eyepiece.

It's easy to point the scope at the sun--you just move the scope until the shadow of the tube is as small as possible.  For safety, I make sure all the observers are on the side of the telescope away from the eyepiece.

With a 27mm Kellner eyepiece, after I got things into focus, the box did show sunspots.  (Note that the big yellowish smudge on the right is glue on the inside of the box, rather than a solar feature.  I will have to stick in a clean piece of card paper there.)  The image was actually a little too bright to view comfortable.  The photo of the projected image worked, though, once I set the camera to minimum aperture and exposure time.  I need to make some registration marks on the projection screen, so that I can take two photos in the future, one with exposure for the bright disc and the other with exposure for the registration marks, and use the registration marks to undo the skewing you see in the photo.

The sunspot positions match those here.

The aperture mask was quite warm, but the eyepiece didn't seem to get hot.

Solar observing safety precautions: Do not look through the eyepiece.  Do not look at the sun naked-eye, either.  Stop down the aperture to prevent the eyepiece from shattering from the heat (which is a waste of an eyepiece, and might cause harm from flying shards), and push telescope away from the sun every couple of minutes to cool off.  Don't use an expensive eyepiece.  Never use the cheap solar filters that screw into the eyepiece.  They can shatter while you're viewing and the sunlight is then likely to blind you (and I had one as a kid that faded with time--it got less and less dark! fortunately, I never used it in the telescope).

Sunday, November 20, 2011


I've tried to see sunspots by using solar projection with a 68mm refractor, with no luck.  Last night, close to sunset, I pointed my 8" Coulter towards the sun, with a 30mm eyepiece and a card in front of it.  I got a very sharp image with a number of distinct sunspots.  Couldn't see any detail in the spots themselves--they were just dots--but they were there.

Normal solar safety rules apply here: Don't ever look through a telescope or eyepiece pointed in the vicinity of the sun.  (I took care of that by making sure that all the observers were on the side of the scope opposite to the eyepiece.)  Cover up any magnifying finder scope (a red dot finder is fine--just don't use it!).  Don't look at the sun while pointing the telescope (my best method for pointing was to move the scope until the size of the shadow red-dot finder was minimized, and then to wiggle the scope until I saw solar glare on the card).  Don't keep the scope pointed at the sun for too long--give it some cool-off time between observations.

On reflection, I should have stopped down the aperture to prevent eyepiece melting.  I didn't have the eyepiece melt, but maybe that was because it was close to sunset.  I am going to try to make a more comfortable projection setup today.  This is all a sort of preparation for the transit of Venus in June 2012.

My solar viewing was before the Waco star party.  Later that night, we were showing Jupiter to girl scouts, waiting for clearings between clouds.  I think everyone who stuck around got a view.  Some of the time the seeing was horrid, but at one time I did see a fuzzy barge atop the northern belt.  After the girl scouts left, the sky mostly cleared up.

Thursday, November 17, 2011

Android moon maps

And talking of the moon, I am working on an Android moon maps app.  I am not so interested in making a planetarium app, as I am holding out for an Android version of SkySafari.

This has now been officially released in the Android Market:
If you don't have access to Android Market, you can download the Lite version here.  If you want to purchase the HD version after that, email me.

Requires Android 1.5.

I will update this post in the comments as needed with new features.  The beta version expires at the end of the 2011 calendar year.

Tuesday, November 15, 2011

My 5000x5000 zoomable moon maps

I posted a bunch of large zoomable moon maps with the help of, which I discovered while looking for a way to view Spinoza dependency graphs.

Sunday, November 13, 2011

Lightening my Coulter 8"

I've been using my 8" F/4.5 scope more, because I just haven't been having the energy to pull my 13" out.

The 8" weighs in at around 40 lbs. I wish it was lighter. I shifted the bearings a couple of months ago so it wouldn't need a counterweight at the bottom of the tube.

And today I finally cut out big triangular holes in the sides of the rocker box.

I sketched out a template in Inkscape, and printed it out in three pieces (it didn't fit on an 8.5x11 sheet), glued them together, and transferred the locations to the wood with a punch.  I used a 2.5" hole saw for the corners of the triangle, and joined them up with a jigsaw cut. It was my first time using my fancy (reconditioned) Bosch 1590 jigsaw. I was pretty pleased. I used a Bosch T234X blade. It cut the tough OSB very nicely, and pretty smoothly (though the hole saw smoked a lot and there was a lot of tearout). The dust blower wasn't strong enough to keep the cut line clear, which was unfortunate (since I was wearing a dust mask, I couldn't blow dust away). Then I painted the exposed wood (with an approximately 1:1:1 mix of acrylic black paint, Titebond II and water). The cut out portions weighed in at a total of about two pounds. Not a big difference, but I find that at around 40 lbs, every pound makes a difference.

Tuesday, October 25, 2011


Alas, I can't report whether aurora was visible as far south as here since I was sick and not observing last night. Here are some gorgeous photos from Norway, though.

Friday, October 21, 2011


Had a look at Jupiter in my 13" during the Live Oak school star party. The south equatorial belt that was missing last year is back--somehow I had forgotten about the disappearance and hence didn't really notice that it had reappeared.

I was surprised to see a very dark spot a little bit east of center on the north equatorial belt at JD 2455856.5754. It looked a little fuzzier than a moon shadow, and possibly slightly elliptical. It moved in the same direction as Jupiter was rotating. Experimenting with my collection of gel filters showed that the spot got much harder to see through a magenta filter. Vivid pink, red and orange also decreased contrast. Green may have enhanced contrast slightly. I hypothesize that the spot was dark red in color.

I also saw the Great "Red" Spot--in the words of a colleague, it looked like an empty area.

Both the dark spot and the Great Red Spot looked very good in my colleague's 8" F/6 with a binoviewer.

Update: I looked on Cloudy Nights. The dark spot is nicely seen here. I am pleased to note that I got the color and shape right with my filter swapping technique: it's definitely dark red and oval in the photo. These spots are apparently known as "barges". More information and links here.

Tuesday, October 4, 2011

The moon, visually

For various reasons, I haven't been doing that much observing for the past half year or so. But I've been out twice this week looking at the moon with my 8" Coulter. I can't really do deep space viewing given the lights that have cropped up in a nearby grassy area, but the moon is all the better for it. I've been observing in and not far from Mare Serenitatis: Posidonius and Cassini were particularly striking, as was Ryma Hyginus together with its central crater. I am finally getting good use of my 5mm ortho eyepiece--it's really nice for the moon, giving a sharp 160X image.

Wednesday, September 7, 2011

Saturday, September 3, 2011

Moon with webcam

While working on an Instructable for how to take pictures through a microscope, I was using a webcam (with lens removed) to take some pictures of the moon, shooting small video sequences and stacking them with Avi Stack.  Conditions were imperfect, but it was fun.

Avi Stack generates photos like these from wobbly video like this:

Sunday, August 28, 2011

Micrometeorite candidates

The kids and I took apart a defective hard drive yesterday, and I used one of the magnets (in a plastic bag, which I then inverted) to fish for micrometeorites in the soil near a downspout.  I found a few plausible candidates, as well as a bunch of surprisingly pretty microscopic ferrous dust.

Here is a particularly pretty area.  The pointer is pointing to a round micrometeorite candidate.  It's stuck to some probably earth-origin stuff--the hard drive magnet magnetized all the samples, so they stick together.  There is also a pretty piece of glass or crystal closer to the top edge.

I ended up preparing a slide with four candidates (one a bit dubious) mounted under a glass coverslip.  It's hard to grab pieces as they are very tiny--though big enough to see naked eye as a tiny dot--and stuck magnetically to other things.  In particular, I lost the round one in the first photo, as it just shot away when I tried to grab it with a toothpick (which looked like a big blunt log under the microscope).  Here's one that didn't get away.  It's about 60% of the size of the ball in the first picture.  You can't tell in the photo, but if you shine the light on this, it's very metallic--a nice silvery object.

I ended up perfecting a method for extracting them.  First, I use the toothpick to sweep the area around it clean, looking in the microscope most of the time.  It's confusing, since the miscroscope reverses the view, but eventually the brain gets used to it.  Then I wet the toothpick with acetone.  The micrometeorite candidate sticks to the toothpick.  I then transfer it to a clean piece of glass.  Because the acetone evaporates so quickly, it's easy to just wipe the toothpick on the glass and the micrometeorite drops off.  I lost two promising samples--especially that nice big round one in the first photo--before I got the above two.

From what I've read, rounded things that look like they were partly melted are good candidates.  Here is a less rounded item that ended up on the slide of the four that I saved.  I don't know how it got there, as I only intentionally transferred three to it, if memory saves.  Maybe it accidentally got carried there.  It looks too rough-edged to be a micrometeorite.  However, I've also read that they can avoid atmospheric melting by being small, so maybe rough-edged things count as candidates, too.  It, too, has a nice shine to it, though the photo doesn't show it.

If you try to view this with bright-field microscopy, of course you just get black silhouettes.  What I did is I taped a bright LED flashlight to the microscope, pointing at the sample, and then I took timed exposures, holding the camera to the eyepiece (sometimes with some sort of adapter to keep the camera in place).  For the second two photos, I found a way of adding more light.  I took the microscope outdoors, and then reflected sunlight onto the slide with a mirror (actually, a hard drive platter--they make lovely mirrors).

The photos were taken with point and shoot cameras hand-held to microscope eyepieces, with some loose-fitting adapters to make it easier. The first photo was with a Sony P100 through the 10X Huygens eyepiece that the microscope came with. The second and third photos were with a Canon G7 through a Rini 30mm telescope eyepiece, using my home-made telescope-to-microscope eyepiece adapter.

Update: I wish I knew how to better identify micrometeorites. The very round one may not be one--see this article.

Thursday, August 25, 2011

Paper craft sundial

Here are instructions for a paper craft sundial I built last night.  The hard part was doing the trigonometry for getting the gnomon to be at the right angle after folding--I hadn't done much trigonometry for a while, especially in regard to laying out a three dimensional object (the gnomon is wider at bottom than at the top).  With the script complete, construction takes about fifteen minutes.

Monday, August 22, 2011

Fix for balance issue on 70mm F/4.3 refractor

My son's 70mm F/4.3 refractor had too easy movement, and couldn't balance with a 32mm Plossl eyepiece (it balanced fine with a light Kellner).  We added a tension adjuster on one side.

The second photo shows the right altitude bearing.  The nut is superglued in place.  If it ever comes unglued, I'll glue something on top of it to keep it in place, or replace it with a threaded insert, or think of something else.  The nut actually was a locknut, but I cut out a lot of the locking plastic, so its locking action is very mild.

And the last photo shows the inside of the mount.  The black ring is a superglued fiberglass washer.  On the other side, under the knob (you can kind of see it in the first photo) there is a superglued washer made from milkjug plastic (rough side facing the wood) so the knob doesn't come undone.

Friday, August 19, 2011

Sundial completed

It's done now, and I made an Instructable with detailed instructions.

Now, can I persuade my kids' school to have it painted somewhere?

Monday, August 15, 2011

Working on sundial

I'm planning to draw a large analemmatic sundial with the kids, with chalk on the driveway. But that's not as much fun as writing a perl script to generate a pdf file with all of the dimensions. The beta version of the script is now running here. Source is also available, of course.
Update: Just executed it in sidewalk chalk. That's the best I can do in terms of permanence, since we rent our house from the University.

Friday, August 5, 2011

Another telescope instructable

And another one of my telescope instructables has been put on the home page of Instructables. This is my 8" F/4 travel scope.

Wednesday, August 3, 2011

Observing on the Gulf Islands

In July, I visited one of the Gulf Islands in British Columbia, where my parents have a sea-side cottage. I brought my airline-portable 8" F/4 scope. The usual curiosity from airport security about the eight pound wooden box in my backpack, but no problems (I just need to allot an extra five minutes).

From my parents' front porch, I looked at and showed them M13, M27, M31/32, M51, M57, NGC 457, the Double Cluster and Albireo. The views were excellent. M27 had a very nice brighter squarish middle, with wings sticking out. I think that's tied for my nicest view of M27 (I've had a good view of it through my 13", too). When looking at M31, I couldn't see M110, perhaps because the M31 area was (a) low in the sky, and (b) that was the direction of Vancouver. NGC 457 (Owl/E.T./Airplane) always pleases people. We also saw a meteor and several satellites.

Once my parents went in, I went after the North American Nebula (NGC 7000). I have never had much luck with it. I saw it in my 68mm refractor with an O-III filter in a past year from the same location, but it was a very faint fuzzy with no structure. This time, still with an O-III filter, it was better due to better aperture: the edges were defined, and I could pan around it with the approximately two degree view of the Rini 30mm in the scope. (I should consider putting in a 2" focuser and using an even wider eyepiece in it.) I kind of got an impression of a shape reminiscent of North America, too.

I had heard that one can see the North American Nebula naked-eye with a filter if the sky is dark, and so I stared at the sky through the O-III filter. And I think I did in fact see it. I think I could also see M13 naked-eye with averted vision (no filter of course). It was almost directly overhead, so that helped no doubt.

The next time we went to a peak in the middle of the island, where I did an unofficial star party. We had almost thirty people show up, unofficially invited by email. We started with Saturn at around 10:15 pm. The rings were sharply defined, though I was using a low magnification due to the scope being fast and there being wind. (I also discarded the light shield due to wind.) I thought that it would be dark by 10:15 pm, but I didn't reckon with northern summer. It was closer to 11 pm before it was nice and dark. However, the party went very well. I showed the same objects as I had shown my parents, plus the Lagoon and Swan nebulae.

I always like it when deep sky objects are naked-eye visible. Overall, on the island, I naked-eye bagged North American (if O-III is allowed for naked-eye; but a filter only blocks light!), M8, M13, M31 and the Double Cluster. Only North American and M13 were particularly special to see naked-eye. M8 is naked-eye from my home, and M31 and Double Cluster are naked-eye from my regular observing location. I think sometimes I can see M31 naked-eye from home, too, but it's hard with the streetlights to the north.

Tuesday, August 2, 2011

My smaller Dobsonian instructable

Looks like my smaller Dobsonian telescope instructable has been featured as an editor's choice and is on the front page of Instructables. Yay!

Monday, August 1, 2011

Instructables space contest

Instructables is running a space-related stuff contest with nice prizes. I posted photos of four of the projects I described in this blog, and I encourage any readers to post their own projects.

Tuesday, July 5, 2011

Progress on AstroObserver for Android

I've been doing other little Android projects, but I'm still plugging away from time to time on AstroObserver. My little demo of scrolling and zooming the stars (40,000 stars, up to mag 8) is in the Android Market. Even though it doesn't do almost anything, it has a few downloads. Maybe it's relaxing to look at stars.

I've been grabbing code from the JAT project (using the version here, because the files I wanted therefrom had GPL2+ notices--though oddly some other files have an Apache notice, which is odd), and learning about UT1/UTC/TT, leap seconds, and other fun things. To keep myself motivated in the project, I think I want to keep on adding code to AstroRender while making sure it always builds, so I always have a working app. I tried starting with AstroTools code (I'll still probably use some of it) but after I made some changes, I had about 180 errors to fix, and I was finding it overwhelming.

I think the next thing I'll do is make AstroRender render for the current time.

I've been learning Java along the way. I'm an experienced C programmer, and a moderately experienced assembly programmer, but object oriented stuff is quite new to me. C++ was just becoming hot when I was finishing my undergraduate years, but at that time the PC compilers didn't produce very good code from C++, and I stuck with C (with occasional FORTRAN77 for some numerical computing code). I kind of like what you can do with objects. I'm going to have a bunch of instances of SkyCalculator subclasses, each of them getting update signals every "tick" (maybe every second?), but updating at different intervals (e.g., outer planets only need to update fairly rarely, every 12 hours for precession/nutation is fine, but some things need to happen every tick).

Wednesday, June 29, 2011

How fat am I?

Suppose I think of myself as shaped like a four-dimensional spacetime worm. We draw diagrams of such things for students—a wide line moving up the board. It is amusing to note that such diagrams are not at all to scale. In a natural unit system, the speed of light will be taken to be c=1. For instance, one might measure time in seconds and distance in in light-seconds. A light second is 299792458 meters long. An average human earthly lifespan is of the order of magnitude of 109 seconds. My largest spatial dimension is about two meters, i.e., about 10−8 light-seconds. That means that my earthly temporal dimension is of the order of magnitude 1017 times longer than my largest spatial dimension. This means that I thought of as a spacetime worm, I am an exceedingly thin worm. If this worm were rotated, projected and scaled so as to be a meter long and maximally thick, a hydrogen atom would be ten million times thicker than the worm.

Moreover, this worm is quite straight. The main variation in its shape seems to be a cork-screw shape induced by the earth's orbit around the sun. But the diameter of the spiral is about a thousand light-seconds, which is a millionth of its length.

So a scale drawing of me in my earthly career as a space-time worm would have me be 1017 times thinner than I am long, and despite a subtle cork-screw, straight to within about one part per million.

Thursday, June 23, 2011

Progress on AstroObserver for Android

I've been learning OpenGL ES 1.0. Here's what I'm getting as a full-sky star map. It looks a brighter and better on my device than on this laptop, though--different gamma settings, I suppose.

I'm modeling the light flux pretty precisely: in other words, I scale the star by a factor proportional to 2.512^(-mag/2) (the 1/2 is there because the light flux is proportional to the square of the radius of a two-dimensional image).

If anybody wants to try the demo (which just shows a rotating sky at maximum speed), it's here.

Thursday, June 16, 2011

More Android dark adaptation goodies

And here is an Android app, which requires a rooted device, to give better control over screen brightness, allowing almost continuous adjustment to very, very close to zero, at least on my device.  This will be useless to you if you don't have a rooted device.

Tuesday, June 14, 2011

Red keyboard for Android devices

I've been working on a red-themed keyboard based on the Gingerbread keyboard.  Should be nice for night use.  Here is a copy.

The screenshot is in Google Sky Map.

Saturday, June 11, 2011

Night mode for Android devices

While astronomy apps tend to have a built-in nightmode, I was very pleased to come across ChainFire3D for Android which, among other things, has a global night mode that works on all apps. The red is a bit too bright, I think (maybe someone should email the developer about it), but otherwise I think it's great.

It needs a rooted device.

p.s. I'm still working away on AstroObserver. It's going more slowly than I'm used to, partly because I've been sick. I'm basing it on AstroTools, but I'm redoing a lot. 

Friday, May 20, 2011

AstroObserver for Android, project beginning

I am starting work on a free open source (GPL) astronomy app for Android, called AstroObserver, thanks to a kind stranger giving me a no-strings-attached gift to buy an Android device (I bought an Archos 43) and Raphael Lelant very kindly giving me the source code to AstroTools under the GPL for me to get a start.

Monday, May 9, 2011

Whole sky image

This is a really neat image of the whole sky that you can pan and zoom.

Saturday, April 16, 2011

Nebula around Lambda Orionis

I had no idea it was there. It's gigantic.

Friday, March 25, 2011

Hunting for meteorites

Inspired by stuff on the web (e.g., here), I went hunting for micrometeorites. I wrapped a magnet with plastic wrap, and ran it through the dirt under one of our house's downspouts. Apparently meteorites have high iron content so magnets capture them. There was some magnetic dust. I then transfered a couple of pieces of it to a microscope slide and had a look. I saw black chunks of stuff with transmitted light, unsurprisingly, but they became pretty and shiny when I shone a flashlight on them. The two largest ones had rough edges. Micrometeorites are supposed to be smoother due to their hot passage through the atmosphere. But moving the slide around, I cam on a smaller piece with smoother edges and interesting texture that matched what one would expect a meteorite to look like. There was some shiny bumpiness, some small pit-like spots and some interesting rod/wave like areas.

I tried to save the tiny piece for future observations. I tried to stick it to some sticky tape, but the goo made it very hard to observe under the microscope. So I ended up dissolving the goo with acetone to recover the piece. As a side-effect, the piece became cleaner and was brightly metallic under the microscope. Unfortunately, I eventually lost it. It was very small, about four or five times longer than wide, and the width was about that of a hair or maybe a touch more. I lost it when I tried to transfer it with the tip of a needle from a dirtier cover glass to a cleaner one, but somehow it just disappeared--I used a powerful loupe to try to find it, but couldn't. Oh well.

At least the kids got to see it. I don't know it was a meteorite, of course. Too bad I lost it before taking a picture.

Thursday, March 3, 2011

70mm refractor project just about finished

And we've almost finished the 70mm refractor.  I may still add some sort of sight for aiming it more effectively, though.

The tripod is made of cherry from a recalled crib that I picked up for scrap wood for free on Craigslist, together with some 1/2" Baltic birch plywood.  I glued two cherry slats side-by-side to form each leg.  The mount is a miniature Dobsonian mount.  The big round cutouts on the mount are to accommodate the oversize focusing knobs.  The azimuth bearing rides on PTFE pads and an old CD.  The altitude bearing uses PTFE pads and a plywood circle.

I had some trouble focusing a GSO 32mm Plossl in it--there wasn't enough focuser in-travel.  I suppose if I want to use that eyepiece with it, I can trim the top of the diagonal a little.

The moon

Here is a great zoomable image of the moon from NASA.

Sunday, February 6, 2011

70mm refractor

Finally we finished the OTA of my son's 70mm F/4.3 refractor.  It uses the Crayford-style focuser I described in my previous post.  I will update with build details later.  Personally, I think it's really cute.

Saturday, January 29, 2011

A simple wooden Crayford-style focuser

My son wanted to build a telescope out of a mailing tube we had, so we bought a 70mm lens (300mm FL).  The part of telescope making that I like the least is focuser-making.  But I think I now have a Crayford-style design that is very easy to make.  It is easier to make than my previous wooden Crayford and helical Crayford, and has about the complexity of my push-pull Crayford but works an order of magnitude better.

It's a block of hardwood (cherry, from an old crib), 2.75"x2.75"x1" in dimensions.  I used my drill press to drill out a 1.5" hole (A) in the middle for the 1.5" outer diameter aluminum focuser tube.  I then drilled a second hole, 3/8" in diameter, all the way through from one side to the other (B), so that hole A and hole B would meet and overlap by 1/16".  This second hole is for the focusing rod.

Finally, I drilled two more holes from one side to meet up with hole B (C and D) for adjustment screws that press on the focusing rod through PTFE pads, and tapped them to fit the adjustment screws simply by forcing a screw into the wood.  These PTFE pads (E) are small strips of 1/16" PTFE, bent into a C-shape, with the back of the C facing the adjustment screws.

I purchased an 8" x 1" x 0.0045" strip of self-adhesive PTFE tape (F) on ebay from for about $3 shipped.  I stuck a strip along one side of the focusing tube.

I then enlarged the 1.5" hole in the middle slightly.  My method of doing this was to use a sanding drum mandrel in my drill press with a somewhat oversized sanding drum (which would stick out on both sides past the work piece), with the work piece resting on another piece of wood with a hole in it, which was on the drill press table.  As a result, I could keep the work piece aligned at right angles to the sanding drum while moving it about so as to enlarge the hole.  I enlarged the hole until it was about 1.56" in diameter.  I then finished the exposed raw wood with Titebond II diluted with water and sanded.  I stuck another strip of PTFE tape (G) inside the focuser hole, opposite where the focusing rod will go.  Then I put it all together, and it worked just fine.

Update 1: I added knobs.  I had some oak circles from using a hole saw on some piece of oak some time ago, and after sanding them (by putting on a bolt and spinning with a drill against a sanding block), I press-fitted them on the focusing rod.  If it starts slipping, I'll drill a hole through the rod and knob and put in a screw.

Thanks: I am grateful to John Wall for the idea of putting PTFE on the focuser tube.

Update 2: I just had a bit of trouble with the wooden thread for one of the adjustment screws getting stripped. Treating the hole with CA glue helped, though.

And I added a screw on one end of the focuser tube as a stop, and I added a screw to hold the eyepiece. Because the focuser tube is only 2" long, so as not to compromise the length of movement, we drilled little depressions in the main block for the screws.

Update 3: And here is a not-to-scale diagram of what the main holes in the block of wood look like.

Monday, January 17, 2011

Various things

It's been cloudy and rainy for a couple of days.

I'll be building a 70mm F/4.3 refractor with my five-year-old son.  Lens and diagonal have arrived ($33, from Sheldon Faworski).  We have a mailing tube of just about the right size.  I ordered some screws and nuts from Amazon to attach the lens to the tube.  I am working on a simplified PTFE-on-PTFE Crayford variant for the focuser, made out of one piece of wood, plus some hardware.  I'll post details once it's done.

I've spent some of the weekend playing with using a Wii remote with an IR pen.  This might be nice for operating Stellarium at public star parties.

Friday, January 7, 2011

Advanced rubylith uses

Rubylith is a deep red plastic sheet, originally used in the printing industry.  Amateur astronomers now use it for such things as covering laptop or phone screens to make them red and help preserve dark adaptation.  It's a nice product for that purpose, but it has other redding-out uses.  In an earlier post, I described a method for using Rubylith to red-out the backlight on my phone.  That method had two problems.  First, the cyanoacrylate glue melted the Rubylith and gummed up keys, requiring extensive cleaning.  Second, light sneaked out around the edges of the Rubylith bits.

But there is a simpler method that I'll explain after a bit of background.  I bought some Rubylith from Jay, an amazingly wonderful ebay seller.  The one sheet I ordered unfortunately got damaged in transit, but Jay immediately sent me two (!) fresh sheets, superbly packed, at no charge.  Along with these sheets, Jay emailed me with a lot of fascinating information on the material.  The directly relevant part of that information is that Rubylith consists of a thicker clear sheet bound by static to a very thin red sheet, and if one cuts very carefully, one can cut through the red sheet layer while leaving the clear sheet intact, and then peel off the red sheet.  I tried to do this, and failed, and emailed Jay that I failed.

Imagine my surprise when today in the mail there came another tube mailer from Jay.  Inside was another free sheet of Rubylith, with squares of the red portion cut out to demonstrate how to separate the red and clear sheets.  (What a great guy!)  It looks like my initial mistake was that I was trying to peel from the edge.  But the trick is you cut out the red portion you want, being careful not to cut through the clear portion, not near the edge, and then peel.  Jay used a #10 X-Acto knife, while I just used box cutters.  Also, you have to know which side has the red sheet--it's less slick side.

Anyway, the red sheet is very thin and very clingy (my calipers say it's about 0.04mm, versus the clear acetate layer which is about 0.10mm).  And I had a use for it.  My phone had a thin latexy membrane between the dome switches and the keys themselves, probably to keep dust out.  I removed that membrane, and cut a clone out of the red layer on the Rubylith.  I took the occasion to clean out some dome switches, and then replaced the original membrane with the Rubylith membrane.

Result: a very nice and deep red on those keys covered by the membrane.  (Some of the redness is from my previous treatment.)

In case anybody is curious, here is Jay's whole email about the history of Rubylith and gel filters.
Changing the subject to night vision, and your search for a red safelight. I'm thinking I should give you some quick background on Rubylith. Even further back in the day (mid-1960's), I used Rubylith for stripping. It's original use was in the printing industry. It is a product that is actually two layers. The red part is incredibly thin, and is bonded (by static electricity, I think) to a much thicker clear plastic.  They are meant to be separated -- stripped -- apart.  Whenever a magazine or newspaper had a photograph they wanted to insert in an article, someone had to manually cut an opening where the photograph would show.  Using a VERY sharp X-Acto knife, and a VERY light touch, a stripper would cut through the Ruby, but not through the plastic. Usually, the stripper would cut a box or rectangular shape. Then they strip away the Ruby.  Actually peel it up off the plastic, leaving a clear box for the photograph to show through. When you get the two new sheets of Rubylith I sent you, you can check this out by experiment.
Since I cannot show you the two different sides of the Rubylith, try this: Take a piece of tape, and stick it to one side of the Rubylith at a corner. Pull up. Either the Ruby will peel away, leaving clear plastic; or you've stuck the tape to the wrong side. Once you get it apart, now is time to experiment. 
I'm thinking the SuperGlue you used, will dissolve the Ruby, but not the clear plastic. And that is why some of the Rubylith seemed to melt, but some of it not. Depending on which side you put the glue. I would not recommend SuperGlue. The workplace where Rubylith is designed to work, uses Rubber Cement. Very, very rarely, would you use Rubber Cement; and then only on the plastic side. Actually generally speaking, glues of any sort were not used with Rubylith.
It is beyond the scope of this letter to describe how the old-style printing processes worked. But Rubylith was an overlay on top of the photograph. It was held in place by a vacuum frame. Then a composite photograph was made; which, using several steps; put the photograph together with the type; and made the final article.
As to Roscolux. Yep, as you might guess, back in the day (late 60's -- early 70's) I worked with that stuff too. I just wanted you to know that the word "gel" is short for "gelatin". As in JELL-O. Roscolux used to be water soluble. You could eat it. The various colors of gel tasted differently, but all would dissolve in water. I'm thinking now-a-day, Roscolux has changed to some kind of plastic-based formula. [Yes -ARP]  But; just; test the stuff with an eyedropper of water first. Or, maybe suck on it. It will either dissolve, or it won't. [It doesn't. -ARP] As to the obvious question, "why gel?", the answer is heat. Roscolux is a product for Theater.  No, not the local movies where you see "Tron." I'm talking legitimate Theater, where the audience sees -- not celluloid images -- but they see real people, standing in front of a real audience, and giving a real performance, in real time. Those people on the stage, must be lighted. And depending on the color of the costumes; and the color of the background; the lights must have color also. Since a typical Theater stage is about half the size of a football field, there must be a corresponding amount of light (think of a night football game). If all the light is just white light, then everything down there on stage will be washed out, faded, by the light. So we color the lights with gels. They must stand up to a whole lot of heat. At a minimum, we're talking a 500 watt bulb. At a maximum, a carbon arc follow spot, which draws 23 amps (about 3,000 watts). Only gel can stand up to this kind of heat. It does not melt. And with this incredible amount of heat, no one worried about humidity. Just check. I'm thinking Roscolux has updated their gels in the last (*ahem*) four decades. Probably they are now plastic, not gel. Just, check first.
Anyway, as I said, Jay is a great guy, so if you're buying Rubylith, I don't hesitate to recommend him. And if you have questions about the product, he's great at answering them. Thanks, Jay!

(By the way, my son wants me to make a telescope for him and his sister out of the heavy-duty mailing tube Jay sent me the Rubylith in.  I am thinking a nice 70mm lens would fit well.)