Sunday, January 09, 2011

Auto-Guiding for Poor Man

I finally got around to modifying my Vixen DD-1 dual-axis stepper motor controller so that it can be driven by PhD (through the GPUSB-AH module from Shoestring Astronomy).

The modification of the Vixen controller was quite straightforward and only took twenty minutes with a soldering iron. I didn't even bother to trace the circuit, but copied the picture from the Shoestring web site (first link above).

I also have a Meade DSI Pro Monochrome (first generation) that I used for some DSO imaging a couple months ago for my astronomy coursework at Swinburne. The problem with the DSI Pro is the tiny chip (Sony ICX424AL) so the field of view is tiny as well.

Since I had a William-Optics field flattener/reducer, I decided that I'll use my Zenithstar 70ED (with the flattener) as the imaging scope, with a DSLR, and use the DSI as the guide camera. My challenge was finding a suitable guide scope ("suitable" meaning "cheap") and securely mount it parallel to the imaging scope.

Based on some suggestions from Stuart on the SingAstro forum, I decided to use a camera lens as the guide scope. As I didn't want to butcher any of my collectible screw-mount Takumars, I decided to butcher this:

A Mamiya-Sekor C 80mm f/2.8 standard lens for the Mamiya M645 SLR. I also took a cheap Meade barlow and cut off the 1.25" eyepiece holder with a Dremel and cutoff wheel (actually a Bosch RTX.. same banana). After judicious application of epoxy, I was able to cement the eyepiece holder to the back plate of the Mamiya lens.

Next step was how to secure the Franken-guider to my Vixen Great Polaris. I did a bit of butchering on the DSI filter drawer holder by drilling two holes in it, then screwing the holder to a piece of wood:

I then epoxied the small piece of wood, to a larger piece of wood and let the whole assembly dry overnight:

After some trimming.. note my ingenious use of a somewhat longer M6 bolt with a wing head, instead of the original M6 hex-socket bolt, to both secure the wooden guider holder, and the original Vixen MT-1 motor.

And with the Meade DSI re-attached, and camera lens screwed on:

I actually got this working before with a less-robust wood bracket, and it guides just fine, except in declination where there's a lot of backlash.

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