RAW16 FITs for short exposure flats

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PetePeterson
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RAW16 FITs for short exposure flats

#1

Post by PetePeterson »

There's been some discussion regarding the need for flats 2 seconds or longer. For short exposures SC automatically uses a video format, and the consensus seems to be that you want your flats in the same format as your images. I'm running an ASI2600MC-P and a friend suggested that perhaps the constraint was not with the camera but with the software. I believe that he's successfully taking 1/10 second TIF flats on his ASI071MM using other software.

1. Is there a problem with overlaying a video format flat on a FITS image?

2. Is the constraint with video only below 1fps due to hardware or software?

3. If there is a problem with overlaying different formats, and this is a SC software constraint, the capture flats routine be altered to allow FITS regardless of capture rate?
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admin
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Re: RAW16 FITs for short exposure flats

#2

Post by admin »

Hi Pete,

the switchover between video and still file formats is just a SharpCap convenience feature that you can turn off. On a one-time basis, just unselect the 'Auto' option next to the capture format control at then you can change that control to the format of your choice. If you want to turn off that behaviour permanently then there is an option on the first page of the settings dialogue – something like 'Start cameras in auto output format' - just untick that.

To be honest, I think it's better to do things that way than to try to work with video format flats (although you could always use PIPP to split them up into single image files).

Cheers, Robin
chromus
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Re: RAW16 FITs for short exposure flats

#3

Post by chromus »

I’ve never needed to do exposures that short for 16bit. I do IF the sky is still dark but I generally wait and do them when the sky is bright enough to do sub 1-sec.

Robin as you know this stuff way better than most -> what are your thoughts on this? Urban myth or is there actually something to it mathematically?
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Re: RAW16 FITs for short exposure flats

#4

Post by admin »

Hi,

I haven't yet seen any reason put forward for taking either long or short exposure flat frames being important that I believe. My personal opinion is that for flat frames all that matters is the number of photons that hit each pixel – if your camera has an FWD of 50,000 electrons then you want to get about 40,000 electrons into the brightest pixels in the flat frame. I can't see how it matters if you do that over 100 ms short exposure with a bright light source or a five second long exposure with the dim light source – both should be equivalent.

Cheers, Robin
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