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Question about QSI 660 darks

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#1 D_talley

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Posted 15 November 2014 - 04:30 PM

I have noticed light areas in my light files and decided to take a dark to see if the light is in it as well.  This is a 20 minute dark, taken at -15 degrees. The image is stretched to show the light patches I see in my lights.

 

Has anyone seen this before?  I have not been using darks with my images but to remove the light patches I tried one last night.  The dark removed the light patch but added noise to the image.  All shots were at the same temp.

 

Can't think of any light leak. Normal 2 inch nose piece for the camera mounted on a AT65EDQ scope. Lodestar guider added to the guide port.  I will remove the guide scope to be sure and shoot another dark.

 

 

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#2 Peter in Reno

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Posted 15 November 2014 - 05:47 PM

Hi Dwight,

 

I usually take darks in a dark closet with the camera out of the scope and covered. I checked my darks (10 minutes at -10C) and I do not see light patches like yours. Also my light frames do not have light patches as well.

 

Make sure there are no shiny or glossy blacks anywhere in the scope, focuser, and imaging train that do not cause any reflections.

 

When I image with external OAG or QSI built-in OAG, I always remove the guider camera (Lodestar or Superstar) and cover the OAG's guide port when taking flats because I was afraid the guider camera might create reflections onto the main camera.

 

Are you seeing light patches with your TEC 140?

 

FYI, I only use master darks to create Bad Pixel Maps. I never dark subtract with lights using Sony's low noise CCDs.

 

Peter


Edited by Peter in Reno, 15 November 2014 - 05:51 PM.


#3 Peter in Reno

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Posted 15 November 2014 - 06:23 PM

Hi Dwight,

 

I took a closer look at my darks for both binned 1x1 and 2x2 and found 2x2 showing light patches just like yours so I looked at 1x1 darks again and light patches are barely seen. I uploaded a sample 1x1 (10 minutes at -10C) and 2x2 (5 minutes at -10C) dark subs.

 

https://www.dropbox....in_030.fit?dl=0

 

https://www.dropbox....0C_001.fit?dl=0

 

I can't really see light patches in my light frames because stars and other objects cover light patches.

 

I would expect these light patches to be removed by calibrating with flats. Have you tried that?

 

Peter


Edited by Peter in Reno, 15 November 2014 - 06:25 PM.


#4 D_talley

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Posted 15 November 2014 - 07:25 PM

I like you never used the darks with this camera because it is noise free but decided to look at the source and cure of the light patches.  I also have not taken flats since the chip size eliminates vignetting.

I think I am picking up something from the camera but will try to run a long dark without anything attached.  I don't think flats will cure this since it is not from the optical train. 

 

I notice the problem when I tried to process this image last night. There is a light spot at the top center of this image.  You may not see it on this reduced copy. I also looked back and think I see the same light spots on my TEC 140 images but am not sure due to the size of the object covering the bright areas.

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#5 Peter in Reno

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Posted 15 November 2014 - 07:50 PM

This is something that could be sent to QSI for them to evaluate. Or you could post it at QSI Yahoo Groups.

 

Your sample dark show light patches at upper left, upper right and lower center. Your latest post said that you see light patch at upper center. Did you rotate the dark or light?

 

You might be correct that flats may not help because I am not seeing anything unusual with my flats.

 

Did you look at my sample darks and are the light patches at same locations as yours?

 

Peter



#6 D_talley

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Posted 15 November 2014 - 08:08 PM

Yes, the light patches in your darks are the same as mine. My image will be rotated from the fits files so the bigger patch is now upper center but shows as lower center in the fits file. It is the nature of the fits files and how they show as images. No rotation was done.



#7 Peter in Reno

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Posted 15 November 2014 - 08:30 PM

I used to have Atik 460EX which uses same Sony CCD as in QSI 660. Here is my sample 30 minute dark at -10C with Atik 460EX.

 

https://www.dropbox....0C_004.fit?dl=0

 

I replaced Atik 460EX because I need a shorter back focus camera with OAG and QSI is one of them so I replaced Atik 460EX with QSI 660wsg. Atik camera does not appear to show light patches.

 

Peter



#8 D_talley

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Posted 15 November 2014 - 08:39 PM

Nice clean dark from the Atik.  So it would seem to be a problem with the way QSI built the camera board or there is a missing shield to keep the stray IR away from the sensor?!?  I posted on the QSI Yahoo board as well.

 

One good thing, I did get my guiding going again.  Set the weights to West heavy and no problems. Not how I normally set the weights but it worked.



#9 Peter in Reno

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Posted 15 November 2014 - 08:54 PM

Hi Dwight,

 

I am glad that you got your guiding working again.

 

So far, I am not dis-satisfied with QSI camera. I also had QSI 683 for a short time and I checked the darks and cannot see any light patches like we see in QSI 660. Another dark sample except from QSI 683:

 

https://www.dropbox....rk_003.fit?dl=0

 

It's possible the high sensitivity Sony chips may pick up very low light leak that KAF-8300 cannot see.

 

You must be thinking about all the cameras I've owned in the past and must think I am crazy. :eyecrazy:

 

Peter



#10 korborh

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Posted 15 November 2014 - 09:01 PM

Could it be picking up the stray photons emitted from the electronics near the chip?



#11 D_talley

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Posted 15 November 2014 - 09:01 PM

Yes, it is very sensitive, may have to cut back on the length of the exposure or start using a good set of darks. I got horizontal noise using only one dark to trouble shoot this problem.

 

You are no more crazy than I am, with the 8 scopes I owned at one time.

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#12 Peter in Reno

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Posted 15 November 2014 - 09:16 PM

That makes me feel better. :grin:

 

Peter



#13 Peter in Reno

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Posted 15 November 2014 - 10:52 PM

Hi Dwight,

 

I think it would be more accurate to show your unprocessed and un-stretched raw dark sample if FIT file format. If it's not an inconvenience, would it be possible to upload your FIT dark sample?

 

Thanks,

Peter



#14 Wembley2000

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Posted 15 November 2014 - 11:51 PM

I have the exact same patches in my 660. I emailed QSI a raw fit and Kevin wasn't concerned about it. Now I just use darks and it goes away when the image is calibrated. The 683 I had did not show this either.

 

Wem



#15 Peter in Reno

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Posted 16 November 2014 - 12:25 AM

I am tending to agree with Korborh about stray photons (or maybe heat) emitted from the electronics near the chip. I have not yet seen negative effects about this. So far I've imaged only two DSOs (NGC6946 and Cocoon Nebula) with this camera and the only issue I am seeing is star bloats from blue filter due to my TEC 140 APO not correcting well below 430nm (violet light). I have Baader Fringe Killer (minus-violet) filter but have not yet test it due to bad weather or cloudy nights lately.

 

I do not cool any cooler than -10C since Sony CCDs have extremely low dark noise and deep cooling is not necessary. If you have been cooling at colder temperatures, try to set cooling set point to between 0C and -10C. It's possible that deep cooling could generate too much heat that Sony CCDs are picking up.

 

Overall, I really enjoy my QSI 660 camera.

 

Peter



#16 Rick J

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Posted 16 November 2014 - 01:35 AM

Only 8?  I still have 10. 60mm, 63mm, 75mm, 90mm, 104mm, 2 150mm (f/4 and f/12), 2 250mm (f/5 and f/8) and the 356mm.  They go back to 1954.  I can't seem to part with a scope once I have it.  The one and only exception was a dime store 75mm reflector a well meaning relative gave me.  It was beyond hope. All 10 have been used for imaging but the 104mm but only because it isn't yet on a suitable mounting.



#17 D_talley

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Posted 16 November 2014 - 10:38 AM

Only 8?  I still have 10. 60mm, 63mm, 75mm, 90mm, 104mm, 2 150mm (f/4 and f/12), 2 250mm (f/5 and f/8) and the 356mm.  They go back to 1954.  I can't seem to part with a scope once I have it.  The one and only exception was a dime store 75mm reflector a well meaning relative gave me.  It was beyond hope. All 10 have been used for imaging but the 104mm but only because it isn't yet on a suitable mounting.

I got my first scope back in 1968 but being in the military and moving too many times have destroyed or lost them.  I have since thinned the herd some because I don't have the clear skies to use them.



#18 D_talley

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Posted 16 November 2014 - 10:47 AM

I have the exact same patches in my 660. I emailed QSI a raw fit and Kevin wasn't concerned about it. Now I just use darks and it goes away when the image is calibrated. The 683 I had did not show this either.

 

Wem

The fact that QSI is not concerned about the noise is disturbing.  My Canon 350d had amp noise, I expect a higher quality professional astronomy camera to be free of noise. Other companies using the same chip don't seem to have a problem.  I guess it is par for the course since their 2 inch nose piece does not support 2 inch filters.  I guess my next move is to contact QSI and see what their fix is.



#19 Peter in Reno

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Posted 16 November 2014 - 02:03 PM

Dwight,

 

Are you seeing light patches from LRGB lights or narrow band lights? I expect NB lights to display light patches more than LRGB lights.

 

Peter



#20 Wembley2000

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Posted 16 November 2014 - 02:34 PM

Dwight,

 

I was also concerned what Kevin said but I did not pursue the matter further. Let me know what they tell you.

 

Peter,

 

I will see them in both if the exposures are long enough. Narrowband is worse due to the exposure time. 

 

 

 

Wem


Edited by Wembley2000, 16 November 2014 - 02:35 PM.


#21 Peter in Reno

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Posted 16 November 2014 - 03:52 PM


I will see them in both if the exposures are long enough. Narrowband is worse due to the exposure time. 

 

Wem

 

Hi Wem,

 

Forgive me for not understanding, you said "will see them ...". I am not sure this means that you will see this issue in the future or you already saw light patches in your LRGB light subs?

 

FYI, I do not see light patches in any of my LRGB light subs. Most of my RGB subs are 10 minutes and Luminance subs are 5 or 6 minutes. The sky limited images overwhelm light patches. But for narrow band, it's typically read noise limited meaning the sky background may not overwhelm the light patches.

 

Thanks,

Peter



#22 D_talley

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Posted 16 November 2014 - 04:33 PM

My RGB are 5 minutes, 10 at most since I live in a red zone. I do not see any light patches in a check of my 10 minute RGB subs of the Cocoon Nebula.  But most of my time is spent narrow band with 20 minute subs. The light patches stand out in unprocessed stacks.



#23 D_talley

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Posted 16 November 2014 - 04:36 PM

Looks to be a lot of comments on the QSI forum.  Others are noticing the problem.



#24 Chris.Baron

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Posted 16 November 2014 - 05:10 PM

This topic is pretty timely; I was contemplating moving to a QSI6120. Given both the 660 and 690 users are complaining of this, one would have to wonder if the 6120 would suffer the same issue. I too have liked the move from a KAF8300 to ICX694 chip for various reasons, but not needing to calibrate images was definitely a benefit. If the response is "calibrate your images", that's less than ideal. Terry of SX seems to think something should be adjusted. He's a good egg so I'd likely think he's right.

 

I too am interested to see what QSI's response is. 



#25 Wembley2000

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Posted 16 November 2014 - 06:12 PM

 


I will see them in both if the exposures are long enough. Narrowband is worse due to the exposure time. 

 

Wem

 

Hi Wem,

 

Forgive me for not understanding, you said "will see them ...". I am not sure this means that you will see this issue in the future or you already saw light patches in your LRGB light subs?

 

FYI, I do not see light patches in any of my LRGB light subs. Most of my RGB subs are 10 minutes and Luminance subs are 5 or 6 minutes. The sky limited images overwhelm light patches. But for narrow band, it's typically read noise limited meaning the sky background may not overwhelm the light patches.

 

Thanks,

Peter

 

Sorry I should have been more clear. I should have stated I see them in heavily streched darks at most exposure lengths getting progressively worse. so if they are in the darks they will be in the lights, depending on how much you stretch them.

 

Wem




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