LRGB Sub exposure length best practice

Questions and answers about processing in StarTools and how to accomplish certain tasks.
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starfield
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Joined: Sun Jan 24, 2021 7:38 pm

LRGB Sub exposure length best practice

Post by starfield »

Got a quick question for you all. I'm new to shooting and processing LRGB. In terms of sub exposure lengths for processing in Startools, does the sub exposure length of my Lum data need to match the sub exposure length of the RGB channels? Since those are less sensitive, I notice some folks shoot longer subs exposure times for RGB and Lum. I wonder if this create issue in the Compose module. To date, I've shot all my subs across LRGB using same sub exposure duration.

Thanks.
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admin
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Re: LRGB Sub exposure length best practice

Post by admin »

Hi,

Ideally the subexposure length of your RGB data would indeed match the subexposure length of the luminance data.

The reason for that, is that when you combine things, you will then be able to add RGB (=synthetic L) to L for an even deeper signal.
If the subexposures differ, then over exposed areas will differ a bit (causing more noticeable artefacts/discontinuities in the highlights), but also read noise will differ, while any non-linearity of your sensor in the highlight will cause slight discrepancies as well (having some bearing on deconvolution for example). None of these things are the end of the world, or constitute big issues, but keeping everything equal is definitely ideal.

Hope this makes sense and helps!
Ivo Jager
StarTools creator and astronomy enthusiast
starfield
Posts: 2
Joined: Sun Jan 24, 2021 7:38 pm

Re: LRGB Sub exposure length best practice

Post by starfield »

That makes complete sense. Thanks!
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