Big Bertha, Turned Edge, Maternal Duck

The skies finally cleared long enough to do some testing of Big Bertha with a black ring about 1.5" diameter, to test whether the problem is a turned edge to the primary mirror.

This indeed appears to be part of the problem. The "two focal lengths" problem seems to be mostly gone, and the image is crisp at a higher power than it was before. The star test diffraction rings are a lot more even than they were before, and the very bright outer ring typical of a turned edge is gone.

Still, the image of Jupiter wasn't particularly crisp at 156x, and contrast was lousy. Perhaps viewing conditions weren't so good. I am at least pretty sure that the major problem is not the size of the secondary mirror. When I put an off-axis aperture mask on the telescope, it doesn't make any appreciable improvement--unlike the situation before I put the black ring on the primary mirror.

I will make a little more of an effort when I have a clear and stable night, and no need to go to bed for work the next morning--and I don't have to deal with a territorial, maternal duck. (The duck has decided to lay eggs under the tarp that covers up the scope. I haven't figured out how to explain to her that these eggs are never going to hatch, and since I move them to the trash every evening, she gets rather upset with me.) If this doesn't clean the image up, the next step is to send it off for interferometry testing, and perhaps refiguring.

Still, it does an adequate job at low power. The Ring Nebula (M57) is pretty cool at 156x (since it is intrinsically a fuzzy object anyway), and even at 221x, it still is pretty decent. I suspect that if I can get this under a dark sky, it will do a nice job on the Whirlpool Galaxy (M51), and Andromeda (M31).

Oh well, it only cost me $625. If I have to put another $500 into refiguring the mirror, it will still be a bargain.