9/22/2010: Maintenance and mods.
Here's what I did: Remove desiccant plug from ST2000XM; cover opening. Remove o-ring from plug and stash in a prominent, safe spot. Bake plug at 375°F for three or four hours. Keep plug in a sealed container while cooling. When plug cools, return the o-ring to the plug. Replace desiccant plug in ST2000XM. We'll see what happens next time. Later that same week, I ordered the desiccant module from Particle Wave Technologies, because clear nights when I put the CCD to work are rare enough that I don't want to lose many while waiting to perform this bit of kitchenery.
9/23/2010: I got my mind right, made a jig, measured twelve times, removed the lens, focuser, and focuser adapter ring from the A-P refractor. I stuffed much of the tube with rags. And then I used the miter saw and a nonferrous metal blade to lop an inch and an eighth off the tube. Everything that would focus before should still focus; nothing that required an extension will need more of an extension, and nothing that didn't require an extension should need one now. In addition, the focal reducer should again be useful for both the SBIG and Canon cameras. And if the FeatherTouch fine-focus adapter can be used in more configurations, better. The whole kit should be more airline friendly too, especially since the focuser threads on and off easily (if I ever intended to fly with it again, which I don't, but who really knows?).
The mail lady just handed me a TeleGizmos telescope cover from HighPoint Scientific. I bought the model made for 6-inch refractors on large equatorial mounts. I thought it might cover virtually all of the 5-inch on the Mach1. Does, too.
Sky trials: total success! The ST2000XM now comes to focus behind the telecompressor and the same custom made spacer I turned to use with the A-P's original focuser. The new-to-me A-P focuser is racked out hardly at all (the telecompressor and 2-inch clamp ring are just barely clear of the focuser body). No diagonal. This imaging train produces an EFL of 546.9mm = F4.3 = 2.79" per pixel. So the nominally 0.75x telecompressor is working at 0.717x. All these measurements are via Pinpoint Astrometry in Maxim DL5, based on the full frames of photos of M57 and environs. Here's a first look at the aligned, stacked, combined and cropped data:
600s total exposure with a full Moon rising behind me. That's a very tightly cropped image (cropped so that you can see some detail in the reduced, websized graphic). 10x20s in each of R, G and B with the chip cooled to -15°C. I controlled the camera in Nebulosity 2, processed data in Maxim DL5 and finished the image in Photoshop CS4. I focused in the L channel, then shot B and G. I finished wtih R after refocusing slightly. (Note that Ha focuses "out" with respect to the other filters.) Ha and luminance data are not used in this image. No guiding. I applied a single 20s dark to each subframe. Look at that delicate central star. This RGB stuff could get to be a habit.
The bizarre vignetting I saw last night is gone.
I packed up the ST2000XM and the computer, threw the TeleGizmos cover over the telescope and mount, and I was inside in five minutes or less. Good deal. And good night!
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