DIY Guide Scope

I noticed that even with a careful polar alignment, I was getting star trails at 336mm focal length and 30-second exposures. A better polar alignment would fix this, but my Vixen Great Polaris sags a bit due to differential load and the tripod hub flexing, so I can never be too sure of my polar alignment from night to night.

The answer obviously is to auto-guide. I used the ZS 70ED as the guiding tube a few nights ago, and got about 20 arc-seconds of peak-to-peak RA error, which is pretty OK except for a large spike once every worm cycle. The Great Polaris has a large drift in declination though:



Today I took apart the declination axis, cleaned it up and loosened it a bit, and lubricated it (with canola oil, since I didn't have any engine grease or white lithium).

I made this short (80mm focal length), fast (f/2.8) guide scope out of an old Mamiya medium-format lens to which I'd epoxied a 1.25" eyepiece holder. Here it is bolted to my William-Optics ZS 70ED, with a Meade DSI Pro camera.

Since I now have the dedicated guide-scope, I can put the DSLR on the ZS 70ED tube now.