Is there much benefit in using luminance frames in heavy light pollution?

[Adam1234]

Well tonights imaging session got cut short before it started due to hazy clouds, so I've resorted to thinking about astronomy rather than practicing it. 

What I'm thinking tonight is, because I live in quite light polluted skies (CO says Bortle 7, but I'd probably say Bortle 8, what with the streetlights), is there any point to shooting luminance frames or am I better off just getting in as many hours of R,G and B as I can?

The reason I ask is because of the LP, obviously I am limited in exposure time, I can get away with 45 - 60s seconds in R, G and B, and 30s max in luminance, which means a helluva lot of subs, many hours of imaging time and lots of processing power.

Am I better off utilising my imaging time getting the hours in on the R, G and B and making a synthetic lum rather than shooting additional lum subs?

[vlaiv]

No.

Luminance achieves much higher SNR in same time as it takes you to take R, G and B each.

In order to even attempt to match 1h of luminance with synthetic luminance from R, G and B - you would need 1h of each of them - that is 3h total imaging time.

Fact that your skies tell you that you don't need longer exposures than say 30-60s - does not mean that you in fact have to take such exposures and can't use longer exposure to minimize number of subs you need to process. You will not loose anything by going longer (if your guiding can support it and you don't get ruined subs due to odd event like cable snag, earthquake or bird landing on your scope ).

[Adam1234]

So I am better off taking luminance subs and increasing the exposure time then?

I'm just worried about overexposing the stars, as even at 60s alot of my stars start becoming saturated and I lose colour, and also worried about the level of noise from LP in longer subs, as again at 60s the mean background adu is quite high

[vlaiv]

4 minutes ago, Adam1234 said:

So I am better off taking luminance subs and increasing the exposure time then?

If you use luminance in your workflow to achieve better images - then of course, use luminance.

Human eye is much more sensitive to noise in luminance data than in chrominance. If you extract chrominance data from RGB and combine that with luminance then it makes sense to shoot luminance data to achieve higher SNR and better image.

As far as exposure length - depends what suits you better. You don't need to go longer, but you can go longer.

In either case - over exposed parts of targets (or star cores) are handled differently. No camera has infinite pixel wells and every camera will saturate on bright stars. Instead of shortening your exposure length - use "filler" subs. Shoot your subs normally and then shoot hand full of very short exposures (really short - like half a second to a second) that you will use to replace over exposed star cores with.

You don't need many of such subs as you'll be using only the brightest parts of them anyway where signal is strong and SNR is good even in single sub.

[Adam1234]

Thanks, I'll try longer exposures on my next target, with some short ones to replace the stars and see how that goes