From: Milton Aupperle <milton@outcastsoft.com>

Date: September 22, 2010 2:15:17 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Sun imaging [3 Attachments]


Dear Wolfgang:


On 22-Sep-10, at 1:18 PM, Wolfgang Heinemann-Reiff wrote:

[Attachment(s) from Wolfgang Heinemann-Reiff included below] 


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.


From your picture, your likely i a similar climate to mine.


Wear a grounding strap on your wrist or pick the camera up, touch a large piece of metal to discharge any static before cleaning it.

 

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.


Pink dots? Isn't the camera a monochrome camera?


Increasing the number of frames did not help either


That's because the dots your seeing are likely caused by holes in the cloth, letting focussed light through. Unless the cloth is moved around, the dots are fixed in position and therefore will stick.


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 ?


I already did.


1) Focus the camera / scope on the sun.


2) Shift the mount sideways so it's pointing at non cloudy clear sky and has no sun reflections either.


3) Adjust exposure time (maybe a second or more time per frame - you will have to play with this) until the image brightness is at 50%. For 8 bit camera, the average on screen should be ~ 128 (out of 255) and in 16 bit modes, the screen should be ~ 32,767 (out of 65535). Use Apples "Digital ColorMeter (in /Applications/Utilities folder) to confirm what the onscreen brightness is.


4) Shoot multiple flats. Probably 3 to 10 frames should work fine. For DSO's, I normally go with 10 frames, For photometric work, I use the average of 200 frames.


5) Relocate the sun and image it with automatic flat corrections applied. DO NOT change focus, rotate the camera or add anything that alters the optical path or your donuts will not be removed and you will need to re-do the Flats.


HTH..


Milton Aupperle