From: Milton Aupperle <milton@outcastsoft.com>

Date: September 22, 2010 9:01:10 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Sun imaging

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