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2022-08-17: APP 2.0.0-beta3 has been released !

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windows 2.0.0-beta3

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Problem with Master Flats versus Single Flat

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(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 91
Topic starter  

I have not done my NB filters with the higher ADU yet, I dread to think what the exposure time is going to be for Ha and SII, they are going to be very long indeed


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(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 91
Topic starter  
Posted by: @wvreeven
Posted by: @stastro

maybe you should try some of these with your Redcat setup Wouter

Thanks for the tip! I generally take flats of between 1 and 5 seconds and make sure that the peak is as far to the right as possible without clipping. This works for Ha but not for OIII and I don't know why. Light leak or internal reflections (possibly in IR) are likely candidates.

Anyway, I am glad that you're managing to solve your flat issues.

Hi Wouter

So the exposure time of the flats clearly does make a difference, I re-did my 22500ADU flats for RGB with a longer exposure time by reducing the intensity of the flat panel, and 22500ADU actually works now.  ADU22500 seems to correct the image better in the corner than the higher ADU Flats too, each one below just has an STF applied

ADU22500

image

ADU32500

image

ADU49500

image

ADU55000

image

So like my Flats from the 15028HNT were all taken at 22500, it seems that I was not going mad, just my exposure time of the flats was not long enough, incidentally I looked back at my flats from my 15028HNT and they were all around the exposure time I now have my 22500ADU flats.

Fully post processing the images, you can see a difference that the different ADU flats have as an effect on the finalised images, each one was processed in exactly the same way with exactly the same settings:

ADU22500

image

ADU32500

image

ADU49500

image

ADU55000

image

So I think ADU22500 is the winner, the image stack is only 85x60S exposures with RGB (No Luminance) at Gain 100

Note to self: Never go with short exposure flats....EVER! 😀

Simon

 


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(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 91
Topic starter  

It would appear that Sky-Flats are working better at correcting the vignetting, so I have a question about Dark Flats.  Because the sky-flats have a varying amount of exposure time due to target ADU and a gradually darkening sky, how do I tackle this with Dark Flats, my thoughts are to take dark flats at the longest flat frame exposure time for each filter and apply that master dark flat to all the flat files.  Thoughts?


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4930
 

You should be able to use darkflats that are in the range of your exposure times (say your range is from 2-4 seconds, I would take darkflats at 3 for instance). Darkflats basically are like bias frames, maybe with a few extra hot pixels (if at all). Personally I like flat panels a bit better, specifically due to not having any variations or the chance of some cloud changing illumination.


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(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 91
Topic starter  

@vincent-mod Thanks

Yeah, I think until I am able to use the M68 connector of the scope (Waiting for an adapter), sky-flats seem to be the only route to actually solving the correction of vignetting.  Once I am using the M68 connector on the scope, the vignetting should be greatly reduced.


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(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 91
Topic starter  

How can I check to see that a Master Dark Flat was used in the calibration of the Flats?  I do not see the MDF being applied in the flats list, and during the processing of the flats, it does not mention MDF at all


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4930
 

They do need to have the same settings (like gain, offset, etc), just like a bias, is that the case? If so, the list should show the tags for MDF in the flats when calibrating.


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(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 91
Topic starter  

@vincent-mod 

I have created my master dark flats, they contain the same exposure, gain and offset as the flats, but you can see here they do not appear to be being assigned to my flats:

image

Nor do I see any mention of the MDF in the console screen:

image

 


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4930
 

I double checked and it isn't actually mentioned in this case, when there is no suitable bias or darkflat then APP will warn for that.


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