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Spots on images


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#1 harbaugh

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Posted 20 January 2008 - 01:47 PM

Well my first night out with the CCD was not exactly a great success.  Clouds, moon, cold, the usual.  Anyway it was a good introduction and I'm slowly learning.

The current problem is spots on the images.  I will try to attach 2 images; one I took Thursday night of the moon and another of my neighbor's window today.  Both show the spots like rain on a windshield.
One spot on the left side just below the centerline is particularly bad.

I admit, both pictures are out of focus, since I have yet been able to focus clearly, and that may be the problem.

If I rotate the CCD in the eyepiece holder, the spots do not move from their position on the computer screen.

Also, I tried two scopes, LS200 and ETX 125 and get the spots on both scopes.  Same trouble focusing on both scope also.

Any suggestions?

Thanks,

Bob
 

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#2 Mike7Mak

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Posted 20 January 2008 - 02:16 PM

Well Bob,

Welcome to the next step on the imaging learning curve. Those spots are usually referred to as "dust donuts". As the name suggests they are caused by tiny specks of dust or smudges on the ccd chip, IR filter, reducer, or any other optical surface within a couple inches of the ccd chip. Dust on the scope mirrors or corrector plate will not cause this problem.

There are two solutions, neither is particularly easy. One is to clean the optical surfaces mentioned. Getting them perfectly clean, and keeping them that way, is nearly impossible.

The other solution is a processing fix which involves taking "flat frames". These are images of an evenly illuminated white screen or the sky around twilight. They produce an image of the dust donuts that is used during calibration similar to dark frames.

Flat frame calibration is a little too involved to explain in one post but you should be able to find plenty of info with Google or in the files sections of many of the Yahoo imaging groups.

...........Mike

http://autostarsuite...hotos/mike7mak/

LX200gps 7" Mak
Takahashi FS78
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#3 Garand

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Posted 20 January 2008 - 02:23 PM

I have had the same issues, and Mark has answered them in posts elsewhere on this board.  Since it is good information I kept it. So, hopefully without stepping on any foot phalanges,  I will paste the answers Mark has previously given.

*************************************************************

Dirty DSI chip:

It has happened to some and not others.
During packing and shipping things can happen.
Here is how to clean it.

Mark
Cleaning the CCD chip on your DSI C or DSI PRO


Parts needed
Q-TIPS
very soft Camel hair brush
Isopropal Alchol 98%
A new clean Spray bottle
Distilled water
Air Syringe ( or compressed air)
Coffie Filters
Kleenex (WHITE SCENT FREE LOTION FREE!!!!!!!!!!!!!)
Patience!!!!!!!!!!!!!!!!!!!!!!!

Use a clean bowl or measuring cup
Strain 1 cup 98% Isopropal Alchol through the coffee filter into A clean container.
Strain 3 cups Distilled water through a new coffee filter  into the same container.
Add 1 table spoon of windex( only the blue windex free of amonia.)
The windex isnt a must but helps in the end process to help prevent streaking.
Stir this mix until mixed very good.
Strain this Mixture through a clean coffee filter into the Clean Spray bottle.
This solution can be used to clean eyepieces,Corrector Plates , filters as well as the CCD chip.



Now use the air syring or compressed air to remove any loose dust on the CCD chip.
Moisten a piece of the kleenex wrapped around the Q TIP untill its wet.
Dont over saturate it.
Very gentily wipe the chip using no pressure or just the pressure of the Q tip if layed on it.
Move side to side then corner to corner.
Now use a clean dry piece of kleenex wrapped around the Q tip to gently wipe off the solution.
Pay attention to the corners this is where dust or dirt is the hardest to remove.
When this is complete use another clean kleenex and very very gently polish the surface.
When this is done use the air syringe or compressed air to blow off residual dust left from the kleenex.
Install camera and do a very short exposure toward a low light source.
Adjust the exposure untill you can see if there is any dust or dirt left on the chip.
The camera dosnt have to be on the scope.
If there are any dust motes left repeat process.
If there are only  1 or 2 motes in the corners gently clean with a kleenex rolled to a point or a very soft camel hair brush.
then blow off with air syringe.

I have used this method on all of my imagers and im dust free.



Mark


********************************************************

This really worked for me.

*********************************************************

Focus:

Try my Diffraction spike focusing method listed here.
I think it will solve all of your focus issues.

Regards

Mark

http://astronomy.qte.../diffspike.html

***************************************************

I haven't taken the time to try this yet - I'm still having fun working on everything else.  But, IMHO, if Mark says it I believe it (go to his site and have a look at the images he produces.  Case closed).  I do plan to try it as soon as I can see something other than clouds.

#4 Mark Sibole

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Posted 20 January 2008 - 09:05 PM

Thanks for answering this Garand.
Saved me a lot of time retyping it out.

Again thanks for the help.

Regards

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#5 harbaugh

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Posted 21 January 2008 - 03:59 AM

Thanks to everyone for answering.  I will devote today to digesting all this.  Sorry for the duplication of questions.

Thanks,

Bob

#6 harbaugh

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Posted 21 January 2008 - 11:10 AM

Ok, I got all the stuff and followed Mark's process.  Did somebody say patience?  After 10 or 12 iterations I finally got the CCD down to one lonely spot.  I don't have to tell you what happened when I tried to remove that last spot!

Anyway, thanks to you guys I now understand the problem and know (sort of) how to fix it.

Next question:  any suggestions for maintaining a fairly clean CCD after getting it clean?  I'd sure hate to go to all that trouble today only to find that the chip is dirty again two days from now when I go to use it.

About all I can see is to keepone of the color filters in place as a bit of a shield.

Bob

#7 Mark Sibole

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Posted 21 January 2008 - 03:29 PM

LOL
Patience is a must.
I used a tf holder listed on the page and added a clear filter to it to keep the dust off of the chip.
http://webcaddy.com....tro/adapter.htm

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#8 Mark Sibole

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Posted 21 January 2008 - 03:39 PM

This TF holder only works on the color imager or if you have the low profile adapter from scopstuff on the Pro model.
Just want to clarify this.

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com




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