[pvelez (Pete)]

Calling all CCD gurus - SBIG gurus even better

Been having fun with the new ST8300M. Have noticed recently some severe vignetting - or so I thought.

Working on some basic photometry this evening - I found that my images developed what appeared to be snow all over the image - except around the centre of the shots. So I inspected the corrector plate and sure enough, I had a fair amount of dew on the corrector plate - mainly inside the scope (I have a schmidt-Newtonian).

So out comes the trusty hairdryer and I clear the dew.

Next shot - same problem?!

I check the corrector plate - clear

I check the primary and secondary mirror - clear

I pull out the MPCC - clear.

Now what?

I take out the MPCC, adjust teh focus - same problem.

So it must be on the sensor itself.

So now what do I do? I had expected that the the camera would be clear of this sort of thing after only a few months of use.

Here are a couple of shots to give you an idea - it was a dewy night and I was running the cam at -10 C as usual.

The attached don't give you a clear picture - if I stretch the images, its an impenetrable fog. You can tell the difference between the shots as the clarity of the image has dropped off between them - count the stars at teh centre of the picture and you can see the difference. There's about 90 minutes between photos.

Open to suggestions

Pete