Spacing or tilt problem?

[Vland]

Hi all, I tried my takahashi reducer 0.73x (CR version) for the first time with my FSQ85.

I can see a distortion problem but I'm struggling to understand the reasons. you can see it happens before the meridian flip and also after, in the exact same ccd area (QHY268M APS-C sensor).
I'm pretty sure the reducer 0.73 should be able to cover an APS-C sensor without issues.

 

The right part of the image looks like my sensor is too close to the reducer, with stars pointing towards the centre.
but why the problem isn't mirrored on the left part?

single exposure 60s, some zoom-in.... (full pictures attached)

upper right corner

 

lower right corner

 

 

upper left

 

lower left

 

 

thanks for any input! 

 

[vlaiv]

Hi and welcome to SGL.

Tilt is really a spacing issue - but only hitting one side / corner of sensor.

Astigmatic stars in right side of the sensor indicate that you have spacing issue on that side - while on left everything looks ok. That means that sensor is tilted.

Often posted image (but I can't guarantee if it is 100% correct or applicable in your case) that suggests what is going on is this:

That means that sensor is tilted so that right side is closer to reducer / flattener and left side is at proper distance.

In any case - you should look into those tilt adjustment adapters.

[Vland]

Thank you. your post makes perfect sense

It's difficult already dealing with all the spacers, adapters, software etc etc without having to deal with a tilted sensor on a brand new camera.
I'll try to understand if this can be fixed and how...
 

 

 

 

[vlaiv]

9 minutes ago, Vland said:

I'll try to understand if this can be fixed and how...

Some of cameras have built in tilt adapter for just that purpose. Qhy one seems to have something similar. Does manual mention anything like that?

Here is example from ZWO manual for their ASI model with same sensor:

In any case - QHY model seems to have same set of front screws that is used to fix the tilt.

[Vland]

13 hours ago, vlaiv said:

Some of cameras have built in tilt adapter for just that purpose. Qhy one seems to have something similar. Does manual mention anything like that?

 

I didn't read anything about that in the manual, maybe it's just not documented?

Anyway before that I will check other mechanical issues... it also could be focuser related. the wheel + camera is quite an heavy setup and the extension of the focustube required to reach focus doesn't help.