Do-It-Yourself Equipment Gallery

Shoestring Astronomy by Doug Anderson

I have built some of my equipment myself, including an observing chair, dew heater, and a Ronchi focuser. I got a lot of ideas from other people's websites, so I thought I should give back to the community by sharing my projects. If you see something here that you want more pictures or information on, just send an email to me at: doug@shoestringastronomy.com

Observing Chair

The amount of comfort that an adjustable height observing chair brings to a long night of observing is hard to put a value on. When your body is in a comfortable, stable position, you will actually see more. Long guided photographs are far easier to achieve. I started with the basic design of the Denver Observing Chair, then made a few modifications. This is a great, easy to build project that doesn't cost a lot. Assuming you already have all the tools, it shouldn't run you more than $35.

The biggest complaint people seem to have about this chair is that it tends to tip forward when the seat is low, so I added the board you see on the bottom. It extends past the front of the chair for stability, and is notched so that the seat-side upright fits in and doesn't slip. A latch hook is added to tie the upright to the bottom bar so that it doesn't come out of the notch when you pick the chair up to move it. The only bad thing about the bottom bar is that the chair will not sit stably on uneven ground. But, if your observing is done on a nice level pad, driveway, or deck, it works great. You might be able to add adjustable feet to make it work better on an uneven surface.

Originally, I used the stair tread material for the anti-slip surface that holds the seat in position. After just a few uses, this material came loose. I replaced it and it came loose again. Then I tried a new approach. I set my table saw blade at a 45 degree angle, and set the blade height so the teeth just barely rose above the plane of the table. Then I ran the board that makes the seat-side upright width-wise across the blade. I moved the board about an eigth-inch, ran it across again, and repeated this for almost the whole length of the board. It took a while, but the result was a nice non-skid surface to keep the seat in place. After applying a two coats of polyurethane, I think it will last the life of the chair, too. It also reduces the cost of the chair, and I think it looks better.

One last addition: a hard foam garden kneeling pad to soften the seat. You can get these for just a few bucks at almost any store that carries gardening supplies. I didn't fasten it to the chair, so I can also use it to kneel on when I have to.

The whole chair folds up nicely so that it is easy to transport.

Guidescope

When I was in about 6th grade (1971?), my mom and dad bought my first scope for me for Christmas. It was a meager 60mm department store refractor, but back then even the department store scopes were of decent quality. There wasn't a piece of plastic on it except for the lens caps. It was certainly enough to fuel my interest in astronomy for a while. I have held onto that scope, and finally brought it out of the closet to be useful again. It can now be mounted to the C-8 as a guide scope.

I made my own mount plates out of oak. The bottom board stays attached to the main scope. The top board stays attached the guide scope. Hard plastic chair feet are used between the board and main scope, and between the two boards. Two knobs run through the upper board and thread into captive nuts in the lower board. The guide scope can be removed and replaced by another board built to hold a piggyback camera. PVC pipe fittings and thumbscrews are used for scope rings.

Autoguiding System

At last, the long awaited autoguider. Using a Toucam Pro webcam, and the excellent GuideDog software (www.barkosoftware.com) running on a laptop computer, autoguiding is a breeze. The setup shown here is for prime focus photography.

The one missing piece was a way to get the laptop computer to talk to the telescope guide motors through the parallel port. Most sites recommend one of several relay boxes. I thought they looked like complete overkill for the task, and I didn't want to add one more box that required power. So, I designed my own interface that uses optocouplers and fits nicely inside a DB25 to RJ12 adapter housing.

Parallelogram Binocular Mount

I love my Oberwerk 12 x 60 binoculars, but holding them steady, or holding them for very long, takes some of the joy out of using them. I have been wanting to build a binocular mount for them, but hadn't dreamed up a good way to build a tripod for it. A few weeks after I removed the optical tube from my old 60mm scope to convert it into a guidescope (see above), I realized the old tripod from it might be the perfect thing. It's not quite perfect, but it does work pretty well. The most expensive piece is the ball head.

Transportation Case

Originally, I started out making the 75 meter trip from house to observatory with just a scope and a case full of accessories. As I added cameras, camera lenses, Telrad, dew heaters, etc, it was taking me three trips to get everything out to Shoestring. So, I took a couple of evenings and made a case that would carry everything at once, can be wheeled out to the observatory using a hand truck, and can be split into two pieces to fit in the truck for a roadtrip. Logbooks and atlases go under the flip-up top. Eyepieces, filters, and other scope accessories go in the top drawer. Camera bodies, lenses, and film go in the second drawer. The scope OTA, dew shield, battery pack, and a few other large objects go in the closet at the bottom. The only problem is, I did not leave much room for expansion!!

Aluminum Wedge

In order to achieve polar alignment with a fork-mounted scope, a device called a wedge must be inserted between the top of the pier and the base of the scope. Wedges can be purchased, but I decided to design one myself. One of my neighbors with a large drill press gave me a hand fabricating it. In hindsight, it would have been easier, and maybe even cheaper, to buy the wedge. But, once it was done, I was very happy with the results.

The bolts between the pier head and the wedge allow the wedge to be leveled. These bolts go through arced slots in the base of the wedge to allow for azimuthal adjustment. The latitude angle of the wedge is adjustable using a turnbuckle, and then is locked down with bolts for stability. Once I spent a few evenings using the drift method to polar align the wedge, it has been rock solid.

Dew Heater

The humidity here in the Midwest makes dew and frost a real problem for observing. I have seen the corrector plate of the C-8 dew up in less than an hour, even with a dew shield. So, it came time to try active dew prevention. I modified the rigid plastic dew shield I already had to include heating elements made from pipe heater tape (sold at most hardware stores in areas where freezing pipes can be a problem). I designed a circuit that used two temperature sensors, one to sense the air temperature, and one to sense the temperature between the heater and the corrector plate holder. The circuit automatically turns the heater tape on and off to maintain the corrector plate about 4 degrees Centigrade above the air temperature. I have not had a dew or frost problem since. I also added a heater to the Telrad finder, and need to work on heaters for camera lenses.

Eyepiece Trays

I wanted a convenient place to put eyepieces, filters, and other small stuff that was close to the business end of the telescope so I wasn't constantly digging in my equipment case during an observing session. I used a white polyethylene cutting board that I bought at the local home improvement store for less than $10. This material is amazing. It is easy to machine with woodworking tools. It is easy to keep clean. It is friendly to your expensive equipment, and I think anyone can get professional looking results. The one tray straps to the pier as shown, has through-holes for eyepieces, and a milled out tray area for filters, etc. The other tray goes above the spreader bar on the Celestron tripod.

Counterweight System

Using a 5-pound exercise weight, some aluminum angle and channel extrusions, and a few other items from the hardware store, I put together a counterweight system that allows two dimensional balance.

Collapsible Tripod Spreader

I really liked the tripod that came with the Orion Sky View Deluxe, except for the spreader. It was a very nice tray that attached to a hinge on each leg of the tripod with screws and wing nuts. It was only easy to transport if the spreader was removed to allow the legs to collapse, but then it was difficult to put together in the dark without loosing a wing nut. I designed this collapsible spreader using some aluminum straps and strap hinges, with a hub cut from sheet aluminum. Now you just lift up on the hub, and the whole thing collapses together with nothing to unbolt. I can also set the tray on the spreader, with a locator pin in the center so the tray stays in place. Now it is far more portable, and much quicker and less frustrating to set up.

Ronchi Focuser

One of the most difficult tasks in prime focus astrophotography is focusing. When a Ronchi screen is placed at near the focal plane, it functions as a large number of knife edges. When the telescope is aimed at a relatively bright star, the result is a pattern of dark and light bars when the focal plane is not at the Ronchi screen, and a more-or-less uniform intensity when the focal plane is at the Ronchi screen. So, how do you locate the Ronchi screen at the plane of the film? I sacrificed a camera body to convert it to a Ronchi focuser. The Ronchi screen is mounted in the plane where the film emulsion would normally be. If this is all you do, you can leave the film door open (or remove it) and look through the Ronchi screen while focusing. I went one step further. I cut a hole in the film door, then mounted a 0.965 inch diagonal and eyepiece that I had from an old telescope. Now the pattern in the Ronchi screen is magnified and far bigger and brighter to look at. Once the telescope is focused, then the Ronchi focuser is carefully removed from the telescope, and replaced with the camera. If both the focuser and the camera are identical, the camera will be in perfect focus. I have yet to use this much, but the initial results were pretty good.

The camera backs I use are old Sears TLS models (manufactured by Mamiya back in the 70's). They use Pentax M42 screw mount lens. Used ones can be obtained at very good prices, $20 to $30, on ebay. They are almost ideal for astrophotography. They have mechanical shutter delay timers, mechanical shutter release, and of course a bulb stop for long exposures. The only thing they use a battery for is the built-in light meter, which of course you do not need for astrophotography. The only downfall I see is that the focusing screen is not interchangable. You can also get great deals on lenses for these thing, if you want to do piggyback astrophotography. I even still use them for my regular photography. I lucked out and one of the camera bodies I bought was in very poor shape, so it was obvious which one to sacrifice for the focuser.