Waxing gibbous moon

There are several different types of astrophotography. The simplest is using a regular camera with a normal lens to take shots of the sky. Slightly more advanced is the "piggyback" method of strapping the camera and lens onto a motor-driven telescope to take advantage of tracking motions for a long-duration exposure. With the "afocal" method, you simply hold a camera and lens up to a telescope eyepiece and shoot the image there. "Eyepiece projection" takes this a step further, removing the camera lens and using an eyepiece as a lens instead, while attaching the assembly to the scope with a T-mount and adapter. And "Prime Focus" dispenses with the eyepiece all together, using the telescope itself as a large lens. My scope was designed specifically with wide-field, prime focus astrophotography in mind, although until last night, I'd never attempted it (or at least, never attempted it properly).

To accommodate the focal plane of the camera (which is different from the human eye) I had to move the primary mirror forward about two inches inside the telescope tube. I'd never done this before, but it went smoothly with the mirror lining up perfectly in the pre-drilled holes (as far as I know, the scope's previous owner never did this, either). This necessitated re-collimation to ensure the mirrors were properly aligned. During this step, part of the brittle plastic housing on the secondary mirror spider popped off. Simply broke and fell away. This threw everything out of whack, but I eventually straighted things out. Sadly, this indicates a new spider assembly isn't something I can put off purchasing as long as I'd hoped to be able to.

There are two significant drawbacks with Prime Focus astrophotography for my scope. First is that since the mirror's position is changed, the scope can't be focused for visual observing. Unlike eyepiece projection, I can't switch back and forth--I'm committed to photography at that point. The second is that unlike eyepiece projection, where I can simply switch out eyepieces to get different magnifications, the magnification is set in stone with Prime Focus. Essentially, my scope becomes a 762mm f/5 prime lens. No zoom. There are benefits, however. The scope as a lens offers great wide-field, deep-space views for astrophotography (especially if the polar alignment and tracking are working properly). It's also a lot brighter without eyepieces in the mix, making focusing somewhat easier (this continues to be the biggest difficulty I've had with astrophotography).

last night clouds rolled in from the north, negating any chance of polar alignment, so I fell back to the old standby of the moon and believe I've gotten my sharpest image of our satellite yet:



I also took a series of Jupiter photos, which was fairly small in the image but showed the Galilean moons clearly. I'll see if I can tweak the images to get something worth posting. I tried some deep-sky imaging as well of starfields and the like, but the wind kicked up and shook the scope too much for anything worthwhile. I did catch a faint streak of a satellite passing overhead, which was nifty, but beyond the novelty factor the images wasn't worth keeping.

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