From: Wolfgang Heinemann-Reiff <wreiff1@t-online.de>

Date: September 22, 2010 1:18:38 PM MDT

To: <Astro_IIDC@yahoogroups.com>

Subject: Re: [Astro_IIDC] Sun imaging

Hi Alan and Milton,

thanks for the valuable hints.

@milton:

No I’m not imaging in the desert. I meant the static electricity which might develop when cleaning the chips cover slip.

The end of the nose piece is covered already as you suggested.

No good meant: using 3 frames as suggested in the manual, pointing the telescope to the sun covered with a white linen resulted in a movie with many tiny pink dots.

Increasing the number of frames did not help either. So after experimenting with different number of frames I gave up.

I just do not know how to obtain a proper flat frame with the combination of ERF together with the very narrow Solar spectrum filter.

Any suggestions how to do this ?

@alan:

I’ll keep you posted on those “brushes”.

Attached please find 2 single Frame grabs out of AIIDC in order to demonstrate the problem with the dust.

Furthermore a picture of my setup after the focuser (4X Telecentric for f/30 at 4480mm focal length).

See attachment visual setup.

Wolfgang

Am 22.09.10 18:05 schrieb "Milton Aupperle" unter <milton@outcastsoft.com>:

Dear Wolfgang;

On 22-Sep-10, at 9:34 AM, Wolfgang Heinemann-Reiff wrote:

Hello Alan and Milton,

thanks for your suggestions.

I have tried so many things to clean the CCD without real success. Some donuts just remain and if I remove these other ones will appear.

Compressed air as well as special brushes or cotton swabs just don't get rid of the dust particles.

The fluids like 99% Isopropyl or Baader’s wonder fluid won’t do the job either because of static electricity.

I'm guessing your imaging in a desert then? Static electricity is only a factor with low humidity, and a desert has large amount of dust too?

The dust may not be where you think it is. The longer the focal length, the further up the the dust can be before it starts creating shadow donuts. That's why many people don't see that their CCD's are dirty until they use long focal lengths. Same thing in Microscopy, the higher the magnification, the more parallel the light is and the more likely small dust motes create big shadows.

You might want to try sealing the CCD off by putting a clear filter on the end of the 1.25" nose piece. That moves the dust further up from the CCD, which might reduce the donut affect. It should also keep the CCD cleaner too as it isn't exposed.

Electrically grounding the Camera before you clean it and then seal it up with the front piece filter would also help dissipate the static electricity too.

Since you said some particles don't move, that might indicate they are actually "pits" on the glass cover plate above the CCD. I use a 20x hand lens (from my Mining Geologist days) to inspect the cover plate for dust and pits.

This is the reason why I thought of using flats, especially since Astro IIDC offers “Flat-Frame correction” on the fly.

However, results with that option activated were no good.

What does "No Good" mean in a quantitative way? How many frames did you do for the Flats and how did you take them?

If your flats are poor or very dark (they should be a brightness of 50% - which for an 8 bit is 128 and for a 16 bit camera is 32,767), then they can not do a good job of correction, so it's always GIGO.

HTH..

Milton Aupperle