Capturing FIT flats for use with DSS

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m32guy
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Capturing FIT flats for use with DSS

Post by m32guy » Sat Jan 11, 2020 8:44 pm

Hi,

I'm trying to capture flats in the FITs format to use with my lights in DSS. To do this, I need to really shorten my exposure time to get a nice histogram. I use an light panel and even at low setting I need to grab the Flat a 30ms. Problem I'm running into is when I capture the flats, it tells me it's grabbing the frames at 1.5 FPS? I wonder if this is resulting in overexposed flats?

Should I think about taking longer exposures by:

1. Building a diffuser to dim my light panel more.
2. Shorten the gain? - On this I was under the impression that DSS needs the flats to be taken at the same gain setting as the Lights. Am I right?

Thanks for the help.

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admin
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Re: Capturing FIT flats for use with DSS

Post by admin » Sat Jan 11, 2020 8:54 pm

Hi,

The 1.5 FPS figure is recording the rate at which frames are being processed and written to output file – that separate to the exposure time used for each frame which should match the value of 30 ms that you have set. As well as the exposure time, other things need to go on for each captured frame including transferring it from the camera to the computer, processing it and writing it out to file if you are capturing - these can all slow down the frame rate below the level that might be expected from the exposure time. In particular writing to fits files can slow things down quite a lot – fits is the slowest file format for writing.

Cheers, Robin

m32guy
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Joined: Sat Sep 21, 2019 9:11 pm

Re: Capturing FIT flats for use with DSS

Post by m32guy » Sat Jan 11, 2020 11:07 pm

Got it. So the individuals frames themselves are exposed at my target 30ms. Thanks for clarifying.

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turfpit
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Re: Capturing FIT flats for use with DSS

Post by turfpit » Sun Jan 12, 2020 9:53 am

m32guy

To check the contents of a FITS file, you can download FITS Liberator from
https://www.spacetelescope.org/projects ... load_v301/

Double click a FITS file and choose the Image Headers tab. The exposure (and other capture settings) will be shown, 0.125s in the example. Note that because the frames are captured faster than they can be written to disk, SharpCap will buffer the frames and write them out after the capture sequence is complete. The delayed writing of frames will be shown in the Notification Bar with the countdown decrementing in 5's.

Flat-in-FITS-Liberator.JPG
Flat-in-FITS-Liberator.JPG (98.81 KiB) Viewed 106 times


Dave

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