Hyperstar Hyper adjustments

 Having some trouble with fine adjustments on the Hyperstar. The new hyperstar is great, but it's very sensitive to focus, tilt, corrector alignment and backspacing. I've been struggling to work through the tilt issues lately. 

Steps

Here's the steps to achieve near perfect alignment when there is negligible tilt in the optics of the system:

1. Zero all tilt adjustments in the system. Interactively test and adjust the height of each adjustment screw push/pull set using a dial gauge on a flat surface while rotating the component under the dial gauge. Do the camera first then the Hyperstar.
2. Center the corrector plate
1. Take the scope out at night and point it straight up.
2. Loosen the corrector plate screws
3. de-focus the system and examine the direction of the star elongation around the edges
4. Adjust the corrector plate centering screws until all the elongation directions point away from the center of the image
5. Tighten up the corrector plate
3. Check for tilt in the system by rotating the HS and checking ASTAP CCD Inspector.
1. If there is no tilt then any imperfections in the HFD values in the 4 corners will rotate as you rotate the camera. If this is the case then move on to 4.1
2. Adjust the tilt until any imperfections in the HFD values in the 4 corners rotate as you rotate the camera.
4. Adjust the back focus
1. Use a variety pack of shims to adjust the backfocus. Once the stars in the corners are round, then you're done

June 3rd

Woot Woot Woot!!!!

Wow, I couldn't be happier! I put a small spacer in -- didn't measure it, but it's maybe 0.3mm, and took a shot and it looks pretty much perfect to me. I can stop!

June 2nd

I did some imaging, then came back to this. Again I did some aligning with it setup and pointing straight up. Starting with it as-is, I took shots as I went. This time I adjusted the corrector plate without ASTAP. When I had bad backfocus setup I could see elongated stars on the edges. The elongation direction was not pointing to the center of the image. So I adjusted the corrector plate using the elongation direction as a guide. When all the elongated stars were pointing to the center of the image I was done. 

First as-is Image:

Unaligned Bad backfocus:

Corrector Aligned, but still with bad back focus:

The ZWO tilt adapter is a bit thicker than the spacer that comes with the ZWO ASI 1600MM Pro, so I switched to the original spacer. This seems to give a better back focus. This resulted in the best image so far, with pretty round stars in the corners, but it can still use some adjustment. I am going to machine a new spacer that I can adjust easier to dial it in even better. But here's the best so far:

Here's ASTAP's take on this image:

May 27

I've got it out again tonight. This night I setup the camera so that it can rotate. I've run it through several rotations, and I am seeing that there is a slight slope to the tilt, but it seems to follow the rotation perfectly. My interpretation of this is that there is basically no camera tilt. Here's an example: 

First Shot

4.85 4.59

  4.58

5.20 5.18

After rotation 180 degrees

5.14 5.24

  4.62

4.43 4.82

It's basically rotated the numbers. If there was camera tilt, then the numbers would remain the same regardless of the rotation. That's not the case, the numbers seem to rotate perfectly. Next I'll try and rotate the Hyperstar to see if it has any tilt. 

Did that -- Tried to adjust the hyperstar, and it was pretty miserable. I undid my adjustments as best as I could and it seems pretty good now. Looking closely at the images I saw some problems so I decided to manually focus. Once I dialed in the focus by hand -- wow it looks great! I'm going to just leave it at this point. Now for some imaging!!!  

May 26

Next night I go out I'm starting off by trying to start with a flattened tilt for both the camera and the HS. I used a feeler Gage to try and flatten the HS, and just zero'd the camera tilt adjuster. I'm also going to adjust the EAF focusing settings so that only the center stars get focused, this may help keep things sane. If things get desperate, I'm going to try and rotate the HS while it's exposing and see if the stars rotate about the center of the image. I may try and use that as a way to adjust the tilt. 

- OK, so I decided to use some machining tools to try and get everything zero'd as best as possible. The HS was out by about 0.002" and the tilt adjuster was out by about 0.001". Pretty much flat now within that precision. I can't say that the sensor in the camera, lenses, corrector or mirror are flat though, but at least two parts should be better. 

-- So I made it out tonight, and found that everything looked pretty much the same. I couldn't pull in one corner. So I tried rotating the HS to see what I could see. The tilt seemed to rotate when I rotated the camera, not with the camera, so maybe it's not camera tilt. I tried adjusting the corrector plate, and that seemed to work beautify. I was able to dial it down to almost nothing. Woot!

May 24th

Had it out last night, and was trying to do the adjustments. I did my best to get it dialed in but one of the directions didn't seem to be able to move in the right direction. This is a bit baffling. 

I made this diagram to figure out where the screws were tilting the image. Screws A, B, and C, where C is the screw in the filter slider slot. A is to the left when the scope is pointing straight up and setup as a hyperstar. T means tighten the Larger screw, and L means loosen the Larger screw. If the T is above the L for that screw, then it means that tightening the screw results in the number from ASTAP in that direction get's higher. L on top means that it get's lower. This is so confusing as I would expect it to be the same for each screw, but by observation, it's different for C! 

I got it as close as I could, but could not get the top right corner to get as high as the others. 

I eventually tried to see if the hyperstar had something to do with it. I loosened the rotation screws on the HS and rotated it. If the hyperstar, and the rest of the scope were perfectly aligned, then the tilt would look exactly the same. It didn't. It was very different. Shortly after this I gave up and turned in.