RGB exposure times more or less than L?

[blinky]

First time shooting LRGB - Im doing L @ 300secs and RGB @ 120s   Is this the way to do it?  RGB less than L?  I have it set for 25 x L and 10 each of RGB, again is this the way to go?

[Laurin Dave]

Other way round... 3 times more photons with L so you need to shorten the exposure to avoid saturating your stars, also depends on your camera,  I have an ASI1600 mono and find that 60s for Lum and 120s for RGB works well, for my scope and my conditions..  as for total integration time for each filter, it depends on what your target is, I’m no expert on this but would suggest You start off with the same and see what you get. 

[blinky]

OK - Have shortened the L to 60 secs, thanks for the tip

[swag72]

I read something years ago, but have never been able to find it since...... While it doesn't relate to specific exposure times between Lum and RGB, it stated that if you wanted a good colour then you should use about 1x Lum to 1X RGB (total exposure time). 

I've pretty much stuck to that since, but I wish I could find it again!!

[MarsG76]

I would have though that it would be the other way around, ie shorter exposures needed for L subs.

[vlaiv]

You actually want to go longer exposures with both - don't shorten Lum exposures.

I agree with Sara that you should at least have total time of L equal to total RGB time. I go for same total time of L and each R, G and B. Don't have less total time in color filters as there will be too much color noise in final image.

As for single subs, this is what I go for:

Don't worry about star saturation in L - you will go for faint stuff and most of your stars will be "overexposed" in the end regardless. So clipped stars in L are not important.

On the other hand if you want accurate star color - don't clip your R, G and B. This can be done in two ways. First is really simple - use short exposures for R, G and B. Other is a bit more involved - use long exposures for R, G and B and then at the end shoot a set of really short exposures in R, G and B (this of course means two sets of darks for color) and you need two stacks that you will combine in the end - using short sub stack for stars only (you can do a bit of pixel math and use long sub stack up to 75-85% value and replace all other values higher than this threshold with short sub stack - but take care to scale short sub stack accordingly).

[ollypenrice]

I find it's target dependent.

For easy processing and painless combination of L with RGB, having 'x' amount of time in every filter (L,R,G,B) is the way.

Once you get the hang of it and are prepared to find more subtle ways of adding L to RGB you will do better to shoot more L. The fainter the target the more I feel this is true.

On targets with high dynamic range you can use your less saturated RGB as the equivalent of a set of short exposures to save over exposed bits.

Once you're in the swing you'll find yourself wanting to be selective about where, on the image, you apply the L. Very often I might have a very deep image of 20 hours' exposure but the stars will come from just an hour (or less) from RGB only.

But for starters I'd suggest you shoot LRGB at parity, the same for all filters.

Olly

Edit: this may be 'too much information' if you're at the stage of experimenting with a new setup but I'll chuck it in anyway. You'll get advice based on, for example, the fact that L passes about three times as much light as any one colour filter. Or advice based on some other aspect of the theory of capture. Personally I don't think this way at all, though it pays to understand it. Instead, I ask myself what I'm going to do with the filtered layer I'm capturing. How is it going to contribute to the final mix? And remember, you don't have to process it in the same way as you processed the other filters either. I do believe, though, that you should always ask yourself two key questions about shooting through filters:

1) Why am I shooting this?

2) What am I going to do with it?

The answers are to be found in your processing workflow, not in the physics of capture.