Suggestions on how to square up a camera to your scope?

[gregbradley]

I am squaring up my Trius to the Honders and its proving a little hard.

Any suggestions about a procedure to square it up> Currently I take focus images and pack it with brass shim trying to get 4 corner stars looking good. Small adjustments seem to make a reasonable effect.

But what can look pretty good with 2x2 binning may have out of focus corners stars at 5 mins 1x1.

Suggestions?

Greg.

[Paul Haese]

That is a pretty small sensor Greg and as such I am surprised you are having such wide variation to squaring. There must be something in the imaging train that causing that variation in tilt. What sort of filter wheel are you using? Is every thing square and seated properly there?

[LewisM]

The entire face plate of SX cameras are tilt/orthogonality adjustable - I had to do it with my SXVR-M25C.

Typical main screw and locking screw arrangement. Good degree of movement permissible.

I need to adjust my SBIG ST-8300 too - it has 4 grub screws on the front that can be tweaked to adjust tilt. I have a small degree of bottom right tilt.

[Shiraz (Ray)]

I squared up my SX camera the same way as Lewis did, with the adjusters on the front plate.

Best method I found was with a laser jig as outlined on the SX website. it will be a fairly fiddly adjustment to get it square enough to work properly with 4.5micron pixels at f3.8 - FWIW, after making up a jig with an old GSO focuser and a laser collimator, it took about 1.5 hours to get mine close enough to work OK at f4.

SX tells how to align on the scope as well, although the alignment screws are hard to get at with some configurations.

http://www.sxccd.com/maintenance_info/Aligning_CCD.pdf

[gregbradley]

Thanks for that Ray.

Yes there must be some flex somewhere. I started using CCD Inspector last night but its graphics interface could stand some improvement. A simple arrow doesn't communicate what you need to do.

I found you need to pack in the opposite direction to the tilt.

Any suggestions on using CCD Inspector?

Greg.

[gregbradley]

I sorted it out.
For anyone interested here's what I did.

Firstly part of the problem came from the change from a FLI CFW 4/5 to a FLI CFW 5/7. The 4/5 olde4r filter wheel had a lip inside the opening for the camera so the camera would rest on that. This then tended to square up the camera automatically. The newer FLI Filter wheels don't have this lip as the intended use of FLI cameras has part of the camera body hard against the front plate of the filter wheel and the camera has a dovetail that fits into the filter wheel opening which is then locked with 2 set screws. That means a smaller camera like a Starlight Express Trius or any camera that has a small cylindrical body can tilt quite easily as the 2 set screws are only near the top not all the way round.

I rummaged through my collection of adapters (quite a large pile!). I noticed a Tak adapter that looks like a jar lid with an opening in the centre of about 62mm.

I have a screw on dovetail fitting that screws onto the end of my Trius camera. It can be 3mm open and still get a good connection to the camera so I can sandwich something in that area. This Tak adapter is about 2mm thick and I faced so the lid part is facing towards the back of the camera otherwise it blocks the dovetail fitting which is needed to engage the FLI CFW.

Viola! Fitted like a glove and very sturdy, flat and free of distortion the allowed easy access to slip a bit of brass shim under any point to pack out the camera.

I focused the camera. Then I inspected all 4 corners. With the Honders if you have tilt to any degree you will get odd looking stars in the corner affected. Radially elongated or simply fatter slightly out of focus stars. I've really got to know the "look" of in focus properly square star images. They are very tight and give the appearance of very small stars, tight, sharp and the small stars look like pieces of sand.

So I save the image and measure it in CCD Inspector. This then shows that its pretty close but one corner is a bit tilted. This could be the sensor not being 100% level or perhaps a slight amount of flex (I found a bad source of flex and fixed it which was simply I did tighten the screws on the front plate of the filter wheel when I installed the filters - duh!). After tightening these I tried to flex the filter wheel and it was quite resistant to flexing whereas before I could flex it a lot more. Good, progress.

A brass shim of .0038mm (yeah I know tiny in one corner seemed to give the best result. Its a bit of a compromise where if you pack out one corner too much it can throw off the opposite corner sometimes so a little is better than a lot. I tried various packings but it started to affect the other corner with the radially elongated star look that I particularly dislike! So back to the thinnest packer the .0038 brass (it cost $15 for a sheet about 300mm square and comes in various thicknesses, I should get an even thinner one for fine tuning as it can be too much of a step if you can believe that). To be clear, I was installing packers between the camera and the filter wheel and under this oversized lid adapter that was about 20mm overall wider than the camera body.

So now refocus and the overall image looks sharp and tight, one corner slightly less than the others but hey, I've already spent 3 nights chasing this down - I'm stoked.

So CCD Inspector is helpful. Which side to pack to correct the tilt isn't so clear with CCDInspector. For my setup it was the same corner as shown in the CCDinspector curvature graphic. That's the one that had to be packed out.

Also using advice from the Starlight Express data sheet about squaring up the camera, you concentrate on the bad corner. Now focus in or out as needed to get it to best focus. Now that tells you if that corner needs to be packed or made to go in (so the other side diagonally opposite would need to be packed out to accomplish that.

Tedious but part of imaging with large sensors and fast scopes or apparently small sensors and fast scopes!.

It starts with having a firm base and good solid connection free of distortion and a clear no gap contact all the way round the camera.
Otherwise you would be chasing a virtually floating camera that will shift every time you loosen it and retighten it to the filter wheel.

Greg.