From: Alan Friedman <alan@greatarrow.com>

Date: September 22, 2010 9:49:25 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Sun imaging

Hi Wolfgang,

I looked at those silicone "brushes" before a recent trip via airplane where compressed air might have been a problem as a carry on item. I didn't wind up buying it, choosing an old fashioned blower bulb instead. Let us know how these work out. Much dust is silica based - it is very important to do as little rubbing as possible.

On my trip I had an opportunity to place my camera on the focal plane of a 17" projected white light disk of the sun. The image was very bright - I had to attenuate the light with an 8nm bandpass Ha filter at the shortest possible shutter setting. The view of dust and other misc. crap was incredible! I'd never seen all this stuff on my sensor before. It looked like a slide of bacteria. Will post a picture when I have a minute.

cheers,

Alan

On Sep 22, 2010, at 11:34 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.

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.

Next think to try would be one of the “magic” brushes the photo industry praises as solution for clean DSLR-Sensors and forget about flats.

Wolfgang

Am 22.09.10 17:01 schrieb "Milton Aupperle" unter <milton@outcastsoft.com>:

Dear Wolfgang ;

As Allan suggested, cleaning the CCD is the best way to get rid of

dust donuts. I use compressed air and a camel hair brush to remove

dust particles. For Dew prints, I use a mix of distilled water,

PhotoFlow and 99% rubbing alcohol with disposable synthetic fiber lens

cleaning sheets for dew prints.

If you want to go the Flat method, I shoot sky flats towards dusk /

sunset for each filters I am imaging with that night. Basically I

pick a southern (for Northern observers) portion of a clear cloud free

sky, point the mount at about 45 degrees and then shoot a series of

flat frames.

You could do the same thing with your scope in the daylight, but you

would likely need to use several second exposures to collect enough

light for the image to reach 50% brightness level. I use Apple's

"Digital ColorMeter" to measure the onscreen brightness of the flat.

Don't forget that your scope needs to be perfectly focussed on the sun

first and then the flats are to be taken. If you change focus after

you shoot the Flats, then the dust / donuts position will shift and

you'll have to re-do the Flats.

HTH..

Milton Aupperle

(PS: Burried in fog and clouds this morning)

On 22-Sep-10, at 5:57 AM, Wolfgang wrote:

> Hello sun imagers,

> my setup for sun imaging consists of a Baader energy reduction

> filter in front of the refractor followed by a 4X telecentric and

> finally a solar spectrum filter behind the focusser.

> The camera in use with Astro IIDC Version 4.06 GM1 is a Point Grey

> Scorpion.

> Being plagued by dust donuts on the camera's chip, I want to work

> with flats.

> Unfortunately the advice offered by Astro IIDC's manual does not work.

> I used 3 frames as proposed with the telescope not pointing to the

> sun but the results are no good.

> The manual states:

> "You should create flat frames by attaching the camera to your

> telescope or lens, then pointing it at about a 50% or so evenly

> illumination object and then taking an image."

> However with the ERF plus the .5 Angstroem filter I do not know how

> to obtain correct illumination.

> When imaging without the Ha filters, I normally use a flatframe-

> lightbox and have no problem to achieve the necessary adu's for the

> DSO-Camera , but I just cant figure out how to do it with the above

> mentioned equipment on the sun.

> I hope that one of the sun buffs can advice a newbee.

> Thanks in advance

> Wolfgang