#21  
Old 20-09-2009, 11:06 PM
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Thanks for that Marki, the trouble is, even that thread talks about stuff that i dont understand, the camera isnt icing up, as the images taken with it look ok, but my flats appear to be in negative.

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Old 20-09-2009, 11:09 PM
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I've been capturing with maxim and stacking with deep sky stacker. You can select QHY8 FITS files in DSS under settings RAW/FITS.
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  #23  
Old 20-09-2009, 11:13 PM
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Duncan, I use a light box I made up and shoot about 40 x 2 second exposures with the light on (light flats) and 40 x 2 second shoots with the light off (dark flats). These are then calibrated in maximdl to make a master (process tab --> make master frames). As others have said you can go to town trying to find the best value for your camera.


Mark
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  #24  
Old 20-09-2009, 11:17 PM
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toryglen-boy (Duncan)
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Originally Posted by marki View Post
Duncan, I use a light box I made up and shoot about 40 x 2 second exposures with the light on (light flats) and 40 x 2 second shoots with the light off (dark flats). These are then calibrated in maximdl to make a master. As others have said you can go to town trying to find the best value for your camera.


Mark
ok then, so a lightbox is the way forward?

i am sure i will crack it, its just at this stage, i dont see much difference between this and the Canon 1000D !!
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Old 20-09-2009, 11:22 PM
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Originally Posted by toryglen-boy View Post
ok then, so a lightbox is the way forward?

i am sure i will crack it, its just at this stage, i dont see much difference between this and the Canon 1000D !!
I edited below. To make master frames in MaximDL 5, process tab --> make master frames. Fill in the fields and it will do it for you. The biggest difference is noise or lack of it. Once you get the hang of it it will make your processing easier.

Mark
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  #26  
Old 20-09-2009, 11:32 PM
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I edited below. To make master frames in MaximDL 5, process tab --> make master frames. Fill in the fields and it will do it for you. The biggest difference is noise or lack of it. Once you get the hang of it it will make your processing easier.

Mark

thanks for all your advice so for Marki

Should flats be applied before debayering?

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Old 20-09-2009, 11:54 PM
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I ended up pointing my scope towards the window this afternoon and doing flats that way. The window has a heavy lace curtain over it and while it is reasonably bright, it is quite diffuse. I then used Nebulosity 1 to take the flats and used the pixel info dialouge box to tell me the the maximum exposure time. I ended up with 1 second flats at about 11000adu. I am using Deep Sky Stacker and you just chuck in all your files and give it 5 or 10mins and it does the lot for you. As long as all your images are the same size in height and width, it shouldn't be a drama. In the panel on the left in Deep Sky Stacker towards the bottom is a title of RAW/Fits. Hit this and then the fits tab, select the "treat all monochrome...." and underneath is a drop down box to select your camera for colourization. I use the AHD option just below this also.
In MaxIm, I select generic for clouring, it is reasonably accurate.
Good luck.
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  #28  
Old 21-09-2009, 12:04 AM
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Originally Posted by toryglen-boy View Post
thanks for all your advice so for Marki

Should flats be applied before debayering?

Yes mate, all calibration is done to the monochrome image before debayering or stacking as it will not work properly. Each sub has to be calibrated individually before debayering or stacking. This can be automated in Maxim to remove some of the grunt work. There is a tutorial on the maxim website under calibration.

http://www.cyanogen.com/maxim_tut.php

Mark

Last edited by marki; 21-09-2009 at 12:18 AM.
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  #29  
Old 21-09-2009, 06:10 AM
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ok, now this is a FAR steeper learning curve than i thought ...

my flats come out in negative, white background with a dark splodge in the middle, and after trying an image of NGC 6357 (as its the redest thing i have ever seen) it came out blue! as did the Horsehead last night ...

That's because you didn't subtract the bias prior to divide the flat into your light subs so you're over correcting. You need to calibrate your frames prior to do anything else. That is debayering & aligning.
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Old 21-09-2009, 06:14 AM
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Hi Duncan so I don't confuse the issue, here's a generic flow that you can refine - should be a good starting point for you:

1_ Take 40 flats at 9000ADU and stack them into one master.
2_ Take 40 bias and stack them into one master.
3_ Calibrate all your light frames (subs)
4_ Save them into a "calibrated" directory
5_ Debayer all your subs into a Red, Green & Blue directory (separate channels)
6_ Select the best sub in each channel to register to and align.
7_ Do your data rejection, stack to mean. Build the three color masters (save as FITS).
8_ Create you color by combining the masters (save as FITS).
9_ DDP/Deconv then save as a scaled TIFF.
10_ Season to taste in Photoshop.
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  #31  
Old 21-09-2009, 06:19 AM
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Ha ha! I tried to do 6357 last night also, with my QHY8 that arrived Thursday from Gama. Great service and expedient delivery!
I have had all the trouble in the world doing the flats until I contacted a more experienced imager. I had an ok colour to the nebula, but I had red rings around the edges of my image. I too thought that the transition from DSLR to QHY8 was gonna be easy, WRONG! What software are you using to capture & stack your files?
This can happen during calibration when you subtract the bias and end up with a negative ADU in the dark areas. All you need to do is a pixel math on your subs to add the negative offset. Aim for 100ADU overall then resave your file as a 16bits FITS, DDP again and you'll be back in business. No fringing or funky colors anymore
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  #32  
Old 21-09-2009, 07:49 AM
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Hi Duncan so I don't confuse the issue, here's a generic flow that you can refine - should be a good starting point for you:

1_ Take 40 flats at 9000ADU and stack them into one master.
2_ Take 40 bias and stack them into one master.
3_ Calibrate all your light frames (subs)
4_ Save them into a "calibrated" directory
5_ Debayer all your subs into a Red, Green & Blue directory (separate channels)
6_ Select the best sub in each channel to register to and align.
7_ Do your data rejection, stack to mean. Build the three color masters (save as FITS).
8_ Create you color by combining the masters (save as FITS).
9_ DDP/Deconv then save as a scaled TIFF.
10_ Season to taste in Photoshop.

Some good advice there fella, although i think i need to go back to school, as i got lost from point one onwards !!

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Old 21-09-2009, 09:00 AM
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Some good advice there fella, although i think i need to go back to school, as i got lost from point one onwards !!

No doubt there's a fair bit of reading but IMHO understanding calibration frames is critical and is going to make your life sooo much easier. There's a lot of litterature about it. Doesn't matter what program you use, the concepts are the same.
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Old 21-09-2009, 05:45 PM
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Originally Posted by multiweb View Post
Hi Duncan so I don't confuse the issue, here's a generic flow that you can refine - should be a good starting point for you:

1_ Take 40 flats at 9000ADU and stack them into one master.
2_ Take 40 bias and stack them into one master.
Thats interesting Marc, I only ever use bias frames when building a master dark. Have never tried it on the flats, will have to give it a go. Perhaps what you are doing is similar to what I do with dark flats??? I take a series of light flats and a series of dark flats then combine to make a master flat.

Mark
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Old 21-09-2009, 05:59 PM
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Some good advice there fella, although i think i need to go back to school, as i got lost from point one onwards !!

Plus 1!!!

Dave
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Old 21-09-2009, 08:30 PM
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Thats interesting Marc, I only ever use bias frames when building a master dark. Have never tried it on the flats, will have to give it a go. Perhaps what you are doing is similar to what I do with dark flats??? I take a series of light flats and a series of dark flats then combine to make a master flat.

Mark
Yes it's the same thing because your dark already contains the bias needed to scale the flat prior to divide. If your bias subtract your flats prior to stacking them then you don't need to do that.

Last edited by multiweb; 21-09-2009 at 08:45 PM. Reason: clarification
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Old 21-09-2009, 09:51 PM
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All this has got me totally confussed. I just treat the the QHY8 as a 16bit DSLR, which it is. That means it can take longer exposures without saturating star colour and since it's cooled, darks are not as important. As for subtracting this bias file from that flat file etc etc , I wouldn't know how to do it, nor does the software I use. I just load everthing into DSS as I was doing with the canon, tell DSS it's a QHY8 and go. I must admit I've only shot a handful of images with it but I've never had a problem either.
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Old 21-09-2009, 10:23 PM
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All this has got me totally confussed. I just treat the the QHY8 as a 16bit DSLR, which it is. That means it can take longer exposures without saturating star colour and since it's cooled, darks are not as important. As for subtracting this bias file from that flat file etc etc , I wouldn't know how to do it, nor does the software I use. I just load everthing into DSS as I was doing with the canon, tell DSS it's a QHY8 and go. I must admit I've only shot a handful of images with it but I've never had a problem either.
Whether it's a QHY8 or a DSLR the process is the same. I did follow the same procedure when imaging with my Pentax *istD. Calibration is something that helps getting the most out of your hard earned data. Bit of reading goes a long way. I used DSS in the past and it confused the hell out of things because I didn't understand how it worked or how I could control things. To me it's a black box. You shove a lot of subs, flats and darks and you get something on the other end. Sometime it works, sometime it doesn't. CCDStack was a giant leap because it forces you to understand what you're doing, not just pushing buttons.
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Old 21-09-2009, 10:54 PM
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Then you are looking for something more than me. I always remember that I first plugged my camera into the scope cos I couldn;t see anything in an eyepiece. A camera was the only way to see the objects, so I'm not after an apod, just a better view. I've used almost all the software available to stack/combine except ccdstack and they are all black box, as you call it. I don't see your images being any better than someone using maxim or dss or anything else, so your controlling what is happening makes it better thoery is crap. Sounds like reteric from an air buss driver to me.

Last edited by Tandum; 21-09-2009 at 11:39 PM.
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Old 22-09-2009, 06:44 AM
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Then you are looking for something more than me. I always remember that I first plugged my camera into the scope cos I couldn;t see anything in an eyepiece. A camera was the only way to see the objects, so I'm not after an apod, just a better view. I've used almost all the software available to stack/combine except ccdstack and they are all black box, as you call it. I don't see your images being any better than someone using maxim or dss or anything else, so your controlling what is happening makes it better thoery is crap. Sounds like reteric from an air buss driver to me.
You're some piece of work dude! Duncan's original query was about "demistifying flats" and the thread is about understanding calibration and other techniques with the QHY8. If you're not interested have a look at another thread instead of posting negative comments. I just share information based on my experience and "what works for me" in order to help others. It's not about who thinks he's right or better or as good as the others. That is your view only. We're all having fun taking pictures and showing them off. No more no less. BTW if you are chasing an APOD you'd better brush up on your spelling for the editorial. IMHO.
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