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poor mans' autoguider

Sat, 03/24/2012 - 13:56 — pierce

so, while waiting out this interminable cloudy/rainy weather (not one clear night since March 9th?!?), I started hacking on a homebrew autoguider.

I acquired a celestron 9x50 straight through finderscope in trade for an old eyepiece I don't use, and I scored a 'golf ball' logitech webcam, which I promptly gutted after determining that it functioned, reducing it to a little 1.5 x 1 inch PCBA with the camera chip on one side, and the USB cable on the other side.

with the finder eyepiecce removed, I found that the webcam would reach focus with it about 1/2" from the end of the body tube of the finder. the finder focuses by screwing its objective element, and that has about 1/2" of range so I knew I only had to be close enough.

after cogitating a bit on the design of the finder, I unscrewed the eyepiece and the end cap, and took the pieces with me down to the local hardware store. After poking around hte poly pipe connectors a bit, I found a black ABS pipe fitting that had threads that fit loosely in the end of the finder body, and had a smooth end that a black ABS cap would fit on, and the webcam board nicely fit inside this cap piece. with a couple turns of gaffers tape, the fitting was a nice press fit with the finderscope body. I drilled a hole in the center of the cap for the wire, and cut notches into the end of the fitting piece so the PCBA would sit on these notches.

There were actually some holes in the clouds early last night, so with this bungied onto the top of my camera tripod, I managed to find venus, and lo and behold, I could see the shape of the planet.

Jupiter had sunk below the clouds and/or trees, and I never did find mars before the crud blocked it, but I think it will work. this webcam's dark slides look awful, however, all sorts of pinpoint star-like white pixels. next properly dark nigh I'll be trying this again.

I haven't glued it together yet, first I want to do some more testing, maybe find a better webcam, once I'm happy how it works, secure the camera board to the fitting and strain relief the cord properly. Right now, its all just kind of pressed together.

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Mon, 07/02/2012 - 23:08 — pierce

Autoguider part 2

I've replaced the chip/board in the camera with a gigaware (radio shack) $29 "1.3 Megapixel" webcam. the board is smaller, so I mounted it on a piece of black card, and secured it with a strip of gaffers tape.

This 1280x1024 chip is about twice the size of the previous webcams 640x480 chip and seems to have much better low light sensitivity, I had PHDguiding watching a mag 6 star for 4 hours near Spica on the night of the full moon. with SNR of around 6-9..

Also, I finally figured out an easy way to mount it. I drilled a 1/4" hole in the side of the tube (removing the lens and camera first, of course!), and used a 1/4-20 nut inside to a Manfrotto RC2 plate, and put it on a photographers ball head thats piggyback on the scope (also for carrying my DSLR), so I can quickly secure the guidecam.

centering it on the main telescopes field of view is fairly easy by starting with a bright star. The guide scope is 1280x1024 and appears to have about 1.5 degrees wide FOV, which calculates to 4.2 arcsecond pixels. PHDguiding had no trouble following mag 6 stars against the moonglow.