Gain setting for LRGB capture

[morls (Stephen)]

Hi,
I'm not sure whether I'm going about this correctly...when changing from filter to filter during a capture sequence the histogram changes, and the captures vary in brightness. At the moment I'm not changing gain between filters as I assume this helps maintain colour balance in the final image. Is this correct, or should I adjust gain for each filter in order to get the best signal/noise ratio?
Cheers
Stephen

[Stonius (Markus)]

The RGB filters cut 2/3 of the spectrum each, so you would expect to have different settings for the colours compared to Luminance.


There are subtle differences between the individual colour filters. Sensors do not have a uniform response across the spectrum, and different objects will emit in different areas of the spectrum.


I usually find that G and B channels tend to be more noisy. Sometimes I'll get more subs in those wavelengths to combat this, but I don't vary the gain or exposure (between RGB filters) because otherwise you'll have different FWHM on the stars.


Markus



Cheers


M

[morls (Stephen)]

Thanks Markus,
Does this also apply for planetary imaging?

[Stonius (Markus)]

You'd still have to change exposure or gain settings between L and RGB filters.


The equivalent to star FHWM in planets would I guess be how much the limb 'bleeds' into the dark areas around it, so I'd keep an eye out for colour fringing, but TBH, it's probably nothing you couldn't manage in post.


As always it a matter of balancing noise from the camera with noise from the atmosphere, if you know what I mean.



In bad seeing I tend to use the gain to get faster exposure times to compensate for the atmosphere.


In good seeing I try to reduce the gain noise.


But as far as differences between RGB filters, I tend to just use exposure to compensate, but not gain. My personal preference is to have the same gain noise on all colours, even if the details are going to vary according to the exposure.


Keep in mind, some of the differences will be because the object doesn't emit as much light in that part of the spectrum ie; when shooting Mars on a blue filter.


But as mentioned sensors themselves are not flat in terms of spectrum response. I don't know how others have fared, but I always have to do a bit of colour balancing in post. I think the only solution where you don't is with an OSC camera.


Cheers


M