Good morning, all. I'm having a heck of a time with my 16" scope. I've never gotten a good image out of it above like 50X power, and it's driving me nuts. For reference, I am not (I hope!) a complete idiot. On my Z8 I re-spotted my mirror, loosened the mounting clips, and re-assembled the back of the scope. I purchased a new Antares secondary and mounted it to a Destiny curved spider with the three spots of glue. On the Z8 I re-assembled from new components I get bang-on collimation and amazing planetary views. It's only f6 and with a much stiffer mirror, but like, I know at least the basics, right??
I am not here to point fingers at any supplier, etc, but to try to solve my problem. I have a 16" scope with an f/4 mirror, 1.5" thick, normal glass, from a small mirror maker but not Cadillac like Zambuto or Lockwood. It's in an 18 point cell with teflon pointed triangles, and a cable sling, rear fan and two boundary fans. I have a 4" Antares 1/14 secondary. I originally had the telescope maker use a 4-vane Destiny curved spider, which was glued on by the three spots of glue again.
Since I've gotten the scope, I've had some kind of triangular distortion or triangular star images (See three sketches below). I use a Visual Paracorr, and have tried everything with and without it. My only TV lens is a 22NT4, so coma correction is not perfect for the XWs.
The top left is a sketch of a defocused star at high power. One one side of focus I get a squashed triangle. It's two very closely spaced bright lines on the outline, and then mostly black. It's not symmetric inside and outside focus.
Mars at 200X shows three discs. I get a very strong trefoil impression - it's three discs. Both of these I've tried moving all over the visual field, to see if it's collimation and coma causing problems, but the shape holds up. Massively defocusing a star (bottom sketch) shows a well centered secondary shadow.
I'm collimating with a self-aligned Zhumell laser that can't be off by more than a mm or two on the mirror. I use this to aim the secondary at the primary mirror spot. I then use a Barlow'd laser to align the primary. I use an offset pupil Catseye autocollimator to fine tune the secondary, and re-check the Barlow laser again. I'm cooling the mirror 1-2 hours before use, fans on. I've checked the triangle pads, made sure they were moving freely and unstuck.
I'm going nuts! This is a pretty severe abberation! I'm not seeing less than ideal star images at 200X, I'm seeing unacceptably ugly stars at 50X+.
I thought maybe the glued on secondary was the problem. I bought a secondary holder from Astrosystems, and mounted it in there. I still had ugly stars. I removed some of the batting, because I thought it was too tight. Last night I went out and set it all up again, and I got the sketches I'm linking below. There's something seriously wrong still occurring.
Is it collimation/alignment? A bad secondary? Bad secondary mount? Bad primary? Bad primary mount? I don't think this is primarily coma, as it gets much worse with mag and I can't find a clear spot in the field where it goes away. Again, I don't want to blame telescope maker / primary / secondary maker, so if you're reading this it's not a hit job, but I am here to solve a problem. The scope maker said they had it out one night for use before I picked it up and it looked good on Jupiter.