Adjusting camera tilt "offline" ??

[Skipper Billy]

I have identified a camera tilt issue and luckily my focuser is adjustable for tilt.

I have CCD Inspector to measure it but wondered if there is any way to make the adjustments and check the results without wasting a clear night under the stars??

I would think I would need to recollimate after each adjustment of the focuser so it could be quite a long winded process but if there is a way of doing it with an artificial star or a laser etc then I would be very glad to hear about it!

Its an ES 201mm f3.8 reflector fitted with a Moonlite focuser, Atik 460 EX camera, EFW2.

Any advise most welcome!

[vlaiv]

I guess artificial star would do very well.

Here is "a procedure" that you can follow:

Have your scope on a mount, you need to be able to point it in different direction (small deflections). Orient camera in X-Y => RA-DEC or similar, so it easy to understand slewing vs on camera star motion. Center the star and focus as best as you can when star is dead center on sensor. Slew star to one corner and measure focus difference - use half width or half flux measure, or even Bahtinov mask. Note which corner is the worst defocus - this one you need to adjust first, adjust tilt to get star close to focus. Move star to center, refocus, test corners and repeat. I use SharpCap for this, it has focusing aid that displays defocus numerically so you can compare values.

Check collimation, and adjust if necessary between steps. It might not be necessary to adjust it.

Ideally you want star focused at center to produce small level of defocus when star is in each corner (depending on field curvature, or equally good focus in each corner if field is flat), but all corners should be of equal defocus.

[Skipper Billy]

That sounds worth trying !!

Thanks very much.