Ad Astra Observatory

I am at a point in my astronomy that I really need to be careful what I’m doing before I proceed with any tuning.

I’ve been able to get away with tweaking and tuning each part of the rig individually, but I am starting to wonder if lots of little errors are merging to become a few really large ones.

I’ve had nothing but trouble with my polar alignment. Among possible culprits:
– mount is not level
– scope is not collimated
– scope is not pointing where I think it’s pointing

Mount level:
My mount is on top of a pier which is attached to 3 bolts set into concrete. The leveling adjustment is by moving 3 nuts under the base of the pier.

However, getting the pier level is not good enough, because the original holes in the pier cannot be lined up with north, because the pier was put in rotated incorrectly. So I had to drill new holes in the pier for the mount bolts to attach to, which means that the bottom of the mount is not necessarily even with the top of the pier. In addition, the bottom of the mount is not necessarily flat relative to the rest of the mount (see below).

So the mount must be leveled while it’s on the pier.

There’s no really easy way to do this; there are 4 points where I check for level, at each “corner” of the base of the mount. According to my iPhone’s level, these are all within 1° of level (around +/- 0.4° for most measurements). I don’t know how accurate this has to be, but there you go.

Verdict: Because I had to drill holes in the pier to line it up, and because I have to use a bubble level to level the mount, the mount’s actual level is suspect.

Scope collimation:
Ah, collimation. I use Veronica for polar alignment. Veronica’s collimation is suspect both because of the scope itself and because of the collimation tools that I use.

Veronica looks like a mostly-stock Orion 8″ f/5 Newtonian. However, Veronica has 4 modifications in particular that are worrisome when it comes to collimation accuracy.
– focuser
– new spider
– new secondary
– collimation bolts

Veronica has a Moonlite CR-1 focuser that has replaced the stock Orion focuser. I have every reason to believe that this focuser is in working order and is installed properly, but it bears mentioning that I have never really tested that the focuser is level to the focus plane, etc.

Veronica has a 2.6″ secondary mirror to replace the original 2.1″ secondary. Is the new secondary correctly installed? Is it far enough up the tube for the focuser to be looking at its optical center? Is it tilted properly? Is it installed on the secondary stalk properly? I have no good way to answer these questions; it “looks right to me”, but what do I know?

The new secondary also sits on a new spider vane, which I had to drill holes in order to mount. Is the new spider correctly installed? Is it tilted? twisted? square? centered? I’ve never had great spider vane performance in this scope (even with the stock spider), and I’m not sure what to make of that.

Finally, the scope now has new primary collimation bolts that are 1″ longer than the stock bolts. Is the mirror still centered in the tube?

I have two collimation tools, a Cheshire sight tube, and a laser collimator. I am convinced that the Cheshire is fine. It’s a pretty simple design and there’s nothing about it that I could have tweaked to mess it up. The laser, on the other hand, does Not Make Me Happy. It’s essentially a cheap $5 laser pointer stuffed into an aluminum tube. I have never had any assurance whatsoever that the laser is pointed down the center of the tube. There are 3 setscrews to adjust the laser, but how does one do that, exactly? For this reason, I usually leave the laser on the shelf, and collimate the scope using only the Cheshire. Can a Newtonian be successfully and fully collimated using only a Cheshire? I have no idea.

Verdict: Veronica’s collimation is suspect. The scope, the tools, and the technique I use are all in question, and I don’t know how to confirm that I’m OK beyond a doubt.

Scope is not pointing where I think it’s pointing:
I recently got Veronica’s rings machined flat where they contact the mount plate, so I have no trouble believing that the scope is orthogonal to the mount plate. The mount plate is a machined piece, I have no trouble believing that the mount plate is orthogonal to the saddle. That’s where my confidence ends. I have removed the Dec axis from the RA axis to clean and regrease the mount. Did I reinstall them properly? The bubble levels in the base of the mount are completely screwed up and not level to the base of the mount, among other things. Is the mount properly machined to have the Dec and RA axes orthogonal? I have a little backlash in the RA axis (put in on purpose), so the mount wobbles a little in RA. Does it wobble in other axes (Dec, El, Az)? Is any of that OK?

Verdict: I’m not sure that the telescope is orthogonal to the polar axis, so I’m not entirely sure that I’m pointing at what I think I’m pointing at.

SOLUTIONS
Apparently, a mount can be properly polar aligned even if it is not level (it just takes an iterative process because adjustments in the axes are not independent).
I can use Pumpkin (which has all stock parts except for the focuser) or the C9.25 (which needs to be collimated) to do the polar alignment.
I’m not sure what to do about orthogonality except to find a way to test it that does not depend upon something else, and then fix it if there’s a problem.