DIY Baby Guidescope

Baby-Guider #1

Having seen a KW Telescope Qwickguider working I thought it might be interesting to try to make one with a small CCD camera and a finderscope.

The 7x50 erect-image Antares finder that I used (shown in it's previous life at left) uses a 50mm, fully multi-coated, cemented achromat. The tube is well blackened and contains a plastic baffle to keep out extraneous light. The screw-on dew shield is finely threaded and also blackened. With an eyepiece it delivered great star images, and very bright ones at that (M33 was brighter in the finder than in most eyepieces of my old C8). The C8 mounting bracket that it came with was not needed for this project and was put away for posterity.

I have two cameras that will function in the Baby-guider. The first is the camera from my stand-alone SBIG ST-4 Star Tracker and the second is a Celestron NexImage camera. The Celestron camera is based on the Phillips ToUCam it has a nice CCD along with WDM drivers and Video4Windows support. This is important as I plan to use it both with MetaGuide and our own TOGA software. My partner in TOGA uses one with the TOGA LX Guider/Focuser in his guidescope and routinely guides on 9th magnitude stars. We'll see how 'deep' it will go in the baby-guider.

The erect-image diagonal was easily removed and put away for future use. A new aluminum tailpiece was machined on the lathe in order to bring the ST-4 camera to focus. Then the focal point of the Celestron camera was measured and the 'shoulder' of the tailpiece was pushed back .280" and a spacer machined to bring the tailpiece back to original size. Now the same part can be used for both cameras; alone with the Celestron and with the spacer inserted with the ST-4. .

Now to mount the baby-guider. I plan to use the BG on both my AstroTech 8" Imaging Newtonian and my Celestron 9.25 both of which have a Ken's Rings style 'half dovetail' accessory bar. To mount the baby-guider a ring assembly was machined from a piece of 3" inside-diameter aluminum tube. This had a wall of 1/4" so first it was cleaned up and thinned slightly in an off-centre manner to give the rings a slight asthetic taper. Then a small 'h-bracket' was machined from some scrap aluminum. The ring assembly was drilled and tapped for a 10-24 screw which served to attach the h-block it to the rings. The top wings of the block are beveled and keep the rings and block aligned perfectly. The lower wings of the H were cut to a few thousandths over 3/4" to fit the accessory bar.

All machining done by Dave Rubenhagen of DAR Astro

Baby-Guider Schematic

Baby-Guider Part Deux

A second Baby-guider based on an AstroTech 50mm finder was built along side the Antares. This one needed some machining done to slightly shorten the tube and the threaded end-plate to allow the NexImage to reach focus. Then the ocular hole was opened up to 1.25" some set-screws added to hold the camera.

The clamshell mount for this one is from an old Tasco refractor with the thumbscrews added. The mounting bar to attach it to the Orion ED80 is of sealed and painted maple.

My friend Doug, the owner of this one, was able to guide on stars down to 8.2 magnitude from his small-town Indiana yard with the shop lights on. Here is a clip from a 15 minute shot he took.

Note the round stars.

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