has anyone have any idea what is causing this

[cardconvict]

here is a pic of m33 and in the top left hand corner the stars have turned in to donuts and i have,nt a clue what is causing this the image was taken with a canon 500 full spec c9.25 on a EQ6 any ideas as because the rest of the image is ok

[MartinB]

It looks like the image is going out of focus in this corner because the focal plane isn't flat (and inherent problem with most scopes and particularly with SCTs). The reason it's only affecting one corner is likely to be that the chip is very slightly tilted in relation to the optical path. This is the problem with big chips:(

[ollypenrice]

I'm sure Martin is right. This is without the reducer flattener? Your first step would be to try with one of those, I guess.

Also have a look at how the camera is attached. Maybe there is play between nosepiece and focusser which turns into a tilt when the nosepiece is locked down by the screw(s.)

Olly

[cardconvict]

thanks olly, martin olly yeah sorry this is with a focal reducer in place i have checked the nose piece and still nothing i'am starting to think that my sensor is not square just checking out gary honnis web site for any clues

[ollypenrice]

Try rotating the camera while on the same target to see if the defect changes sides. If it does, it's the camera. If it doesn't, it's the optics - or so it would seem to me.

Olly

[barkis]

If the camera has been modified, then is there a chance one of the shims has dropped out during the procedure. These shims are there for the purpose of squaring the sensor to the optical axis.

On of mine dislodged as I was refitting the sensor, and I was just pleased I noticed it.

Look at stage 21 here. http://ghonis2.ho8.com/rebelmod450d3.html

Ron.

[cardconvict]

yeah the canon 500 is torxed down not on shim's i have found a link on how to square my sensor off but i need a mosquito net to do this

[barkis]

yeah the canon 500 is torxed down not on shim's i have found a link on how to square my sensor off but i need a mosquito net to do this

Ah!, I wasn't aware of that. Good Luck with it anyway.

Ron.