Hi. I am using a QHY410c and SCPro. My flats dont seem to be working. Vignetting and OAG shadows arent being removed. In trying to solve the issue I looked at the flats histogram in ImagesPlus - the peak is way to the left and very dissimilar to the one I thought I had set in SCPro using Still mode.
I set the SCPro exposure according to the histogram and use a lightbox a few metres from the telescope.
Does the SCPro stretch the histogram?
How do I set the correct histogram parameters? and get correct flats?
GlennB
Flats not working
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Re: Flats not working
Hi Glenn,
the horizontal scale of the main histogram is never 'stretched', so peaks are at the %level shown in that histogram. Maybe you can share a link to the problem flat frame so we can advise. Also, don't forget that it is important to use dark frames (or bias offset) when using flats, otherwise they may over or under correct.
cheers,
Robin
the horizontal scale of the main histogram is never 'stretched', so peaks are at the %level shown in that histogram. Maybe you can share a link to the problem flat frame so we can advise. Also, don't forget that it is important to use dark frames (or bias offset) when using flats, otherwise they may over or under correct.
cheers,
Robin
Re: Flats not working
Hi
Thanks for the reply.
Dropbox file link is here. https://www.dropbox.com/s/xhg7lxwec5dv3 ... T.fit?dl=0
Thats a 63Mb masterflat RGB file. Looks way underexposed, so I would need more time but I thought I had it set to mid histogram.
GlennB
Thanks for the reply.
Dropbox file link is here. https://www.dropbox.com/s/xhg7lxwec5dv3 ... T.fit?dl=0
Thats a 63Mb masterflat RGB file. Looks way underexposed, so I would need more time but I thought I had it set to mid histogram.
GlennB
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Re: Flats not working
Hi Glenn,
interesting - it looks like there are 3 colour channels in that master flat - the middle channel (green) is brighter than the other two. There is also a pronounced dark area on the left hand side - that might have come from incomplete flat illumination.
Anyway, it's difficult to tell exactly what is going on, since I'm not sure what software/settings you used to create the master flat from the individual flat frames. The master flat claims to be 20 bits per pixel, which is odd.
Could you please also share one of the individual flat frames that went into the master flat - maybe comparing the two will help reveal what is going on.
cheers,
Robin
interesting - it looks like there are 3 colour channels in that master flat - the middle channel (green) is brighter than the other two. There is also a pronounced dark area on the left hand side - that might have come from incomplete flat illumination.
Anyway, it's difficult to tell exactly what is going on, since I'm not sure what software/settings you used to create the master flat from the individual flat frames. The master flat claims to be 20 bits per pixel, which is odd.
Could you please also share one of the individual flat frames that went into the master flat - maybe comparing the two will help reveal what is going on.
cheers,
Robin
Re: Flats not working
Thanks again. I think the masterflat frame was spat out by DeepSkyStacker but it looks like the format from ImagesPlus. I'm confusing myself.
This is a link to a single flat frame
https://www.dropbox.com/s/t22a4mb70avjs ... .fits?dl=0
The dark patch on the left is the shadow of the prism of my Lumicon newtonian giant OAG. I have addressed a possible misalignment of the camera due to my having to fit things together with thumbscrews.
I've had a better read of the info in the SC manual. I see that it is preferable to use a monochrome flat for this OSC camera so I'll try that. ?
GlennB
This is a link to a single flat frame
https://www.dropbox.com/s/t22a4mb70avjs ... .fits?dl=0
The dark patch on the left is the shadow of the prism of my Lumicon newtonian giant OAG. I have addressed a possible misalignment of the camera due to my having to fit things together with thumbscrews.
I've had a better read of the info in the SC manual. I see that it is preferable to use a monochrome flat for this OSC camera so I'll try that. ?
GlennB
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Re: Flats not working
Hi Glenn,
thanks for sharing that frame - the levels are indeed low, with the histogram confined to about the bottom 33% of the available brightness range. I would say that the frame was underexposed by roughly a factor of 2 compared to an ideal flat frame.
If you get a chance, the best thing may be to capture another flat frame and at the same time a screenshot showing the SharpCap histogram and camera controls values so that I can try to understand what may be going on.
I personally suggest using monochrome flats to avoid having the flat correct the colour balance of the image, but many achieve good results without this. It is certainly something to try, but do not consider it a hard-and-fast rule.
cheers,
Robin
thanks for sharing that frame - the levels are indeed low, with the histogram confined to about the bottom 33% of the available brightness range. I would say that the frame was underexposed by roughly a factor of 2 compared to an ideal flat frame.
If you get a chance, the best thing may be to capture another flat frame and at the same time a screenshot showing the SharpCap histogram and camera controls values so that I can try to understand what may be going on.
I personally suggest using monochrome flats to avoid having the flat correct the colour balance of the image, but many achieve good results without this. It is certainly something to try, but do not consider it a hard-and-fast rule.
cheers,
Robin
Re: Flats not working
Glenn
I have been using an Altair 183C OSC for capture. My flat frames have a green caste to them. Flat frames are captured using a electro-luminescent panel mounted in a plasticard frame.
At capture time the log histogram looks like this. I concentrate on getting the L histogram around 50% saturation.
The resultant frame looks like this in FITS Liberator. A mean ADU of ~30,000 keeps the histogram away from the sides.
Feeding the untouched lights, flats, bias and darks into processing software (Astro Pixel Processor or PixInsight) gives me results like this:
This might give you some idea of what to aim for. Certainly an example like the first image would be useful to help debug your issue.
I have never converted OSC flats to mono, so I am unable to comment on that.
Dave
I have been using an Altair 183C OSC for capture. My flat frames have a green caste to them. Flat frames are captured using a electro-luminescent panel mounted in a plasticard frame.
At capture time the log histogram looks like this. I concentrate on getting the L histogram around 50% saturation.
- colour-flat.JPG (59.66 KiB) Viewed 934 times
The resultant frame looks like this in FITS Liberator. A mean ADU of ~30,000 keeps the histogram away from the sides.
- colour-camera-flat-frame-in-FITS-Liberator.JPG (145.83 KiB) Viewed 934 times
Feeding the untouched lights, flats, bias and darks into processing software (Astro Pixel Processor or PixInsight) gives me results like this:
- M31_crop_DBE_NR_sharpen.jpg (473.96 KiB) Viewed 934 times
This might give you some idea of what to aim for. Certainly an example like the first image would be useful to help debug your issue.
I have never converted OSC flats to mono, so I am unable to comment on that.
Dave
Re: Flats not working
Thanks Robin and Turf, Ill do that.
Glenn
Glenn