Hello all
I have just purchased a FLI Proline 16803 with CFW5-7. I have attached it to my FSQ106N, and my optical train is this:
FSQ drawtube (CAA removed) - Custom Adapter (giving a complete screw fit attachment) - CFW5-7 and then the camera. In this arrangement, the focusser on the FSQ is only extended by about 8-10 mm.

However, my stars are terrible at the edges...heavily elongated even in 30 second exposures. The elongation does appear to be radial. This should be a good, flat field since the image circle of the FSQ exceeds the Proline chip. Indeed, John Gleason takes perfect images with an identical set up. I am highly suspect that the FSQ is miscollimated, but there is a manufacturing flaw with the CFW, which gives rise to tilt...FLI are sending me a new one.

I have taken 2 images for you to look at...one is inside of focus, the other, outside of focus by the same amount. The links are here.

http://www.martinpughastrophotography.id.au/PLUS100Counts.jpg

http://www.martinpughastrophotography.id.au/Minus100Counts.jpg

The vignetting also seems odd to me, and uneven.

Do these images reveal anything to anyone? Other than the obvious of course that the stars are rubbish off axis.
Thanks in advance.

Martin

Hi Martin,

Doesn't look like a focuser or filter wheel tilt is causing this -- the star pattern is very symmetric across the fov.

Since FSQ is supposed to have a flat circle of about 85mm, I would say the objective/field flattener combo needs adjusting and possibly collimation.

Just to make sure, try imaging without any filters in the light path: some filters may cause distortion at certain light incidence angles.

Regards,

-Paul

Thanks Paul

there is no field flattener in the optical train. Its just the native FSQ at a native focal length then the camera.

I have already done this through several filters and even removed a filter and imaged through the blank hole....symptoms remain.

It does look as if this is going back to Japan

cheers
Martin

....the other thing as well Paul ...regarding your statment on symmetry....the on-axis stars are fine in my opinion...just at the edges where they turn to lemons....and you're right...with an 85mm flat field..there shouldnt be an issue here.

cheers
Martin

Hi Martin,

FSQ is a Petzval design, and has a field flattener positioned near the middle of the OTA, far from the objective. That's the FF I meant.

I would recommend that you have the OTA checked out by your local Tak dealer or Tak factory, as it doesn't seem to be performing to spec.

Regards,

-Paul