450d filter removal problem, advice please :)

[SamAndrew]

I took the IR filter out of my 450D last night, and was very excited to find it still worked once I put it back together

However I took a few test subs of m42 and the stars were all a bit out of shape; I initially thought it was poor tracking, but the shape was very consisten between all the subs, I switched to my Nikon 3100D and the stars were perfectly round.

The shape I'm getting is the classic comet shape associated with coma across the whole image in 1 direction, is it possible this is due to the CMOS chip not sitting flat in the camera ?

has anyone else experienced this ?

I will post a picture up later if it helps

Thanks in advance !

[Daniel-K]

a picture will help but it may be collimation??

[Psychobilly]

I would be inclined to download and print out a Lens test chart and take some pics of it with the camera and a standard lens on a tripod setup so its square onto the chart...

There are Hires test charts available on the web for download.. a Square grid or dots chart might also help see whats going on...

http://www.northlight-images.co.uk/article_pages/test_images.html

The ISO 12233 Chart is one I have used to test Camera lenses in the past...

You can generate a whoel range of grid test charts here...

http://www.imatest.com/docs/distortion/

Whillst these are normally for testing lenses .. you can also use them to see if the sensors sitting properly... Were there any shims in there ? if there were did you replace them in exactly the same place they came out of same shims same corners?

Peter...

[SamAndrew]

thanks for the responses

just attached a crop of part of the frame, all the stars are this shape and pointing in the same direction across the entire sub.

I also thought collimation, but I tried some test shots with my other camera and the stars were perfect, I also checked with a laser.

The lense test charts are a good idea, but I don't have any lenses for this camera, doh! I bought the body purely for astrophotography.

I'm taking the camera apart again now, shouldn't take too long now that i've done it once and i'll check everything is sitting properly this time.

[SamAndrew]

update :

Took the camera apart, cleaned out some dust that i missed the first time and put it back together again, I think the sensor was sitting on the shims properly the first time, but the vibrating screen infront of the sensor might not have been clipped down properly.

attached the camera to my st80 and took some test shots of some street lights, and it seems to be sorted, now i just need to wait for a clear night to try it on some stars.

[Psychobilly]

Glad it looks like you have got it sorted