When planning Mono images - how much time to allocate to L, R G and B?

[g__day (Matthew)]

So lets say I had planned to image a Nebula in LRGB for a total of 24 hours - how much time would folk suggest I allocate to each filter for a non broadband target - are there any rules of thumb - like 40% of time allocate to Luminance data and 20% to each of Red, Green and Blue?

Secondly if one where planning to get say 10 hours of Luminance data - would you go for all the same image duration or split it into something like

1 hour of 60 second shots
2 hours of 120 second shots
3 hours of 180 second shots
4 hours or 240 second shots (presuming this didn't fill your camera light wells)

And for the RG and B filters do the same - but go for longer duration shots by 30% - 50% duration as filters let less light though?

Many thanks for folks suggestions

[Joshua Bunn (Joshua)]

Hello Matt,
Here are my thoughts...
Ive worked on the amount of time you spend, combined, on you colour filters, spend the same on your luminance.
Note, if you capture your colour data at the same resolution as your luminance, you can use the individual colour frames to go towards you luminance data.
As for the ratio of RGB, I think this comes down to the amount of light each filter lets through, the particular target, and the colour response of your chip. Get your RGB weights using whichever method you choose, and combine them using equal exposures with varying weights or varying exposures with equal weights. To get similar S/N between colour filters, add more exposures of a particular colour if all equal exposures... and visa versa.

The duration of the luminance is very target specific, it depends if you want to capture a wide range of brightness and if the target has a wide range of brightness scales. Generally you cant avoid over exposing at least a few very bright stars, but try to avoid blowing out the cores of galaxies and bright nebula. Remember, colours will be more vibrant if kept to no more that 2/3 of the grayscale values.


Joshua

[AdamJL]

Above a certain amount, you don’t even need luminance. RGB will do.
For single night shots, I sometimes do 2xL and 1xRGB. So for a 5 hour shoot, that’s an hour of each colour and two hours of luminance

[AdamJL]

And good advice from Josh, as always

[g__day (Matthew)]

A follow up question - once your data sets get very large - say hundreds of images for each colour channel how do you decide are you better taking the best 20% or the best 80% of images - is there guidance as to how to determine where to draw a cut-off between fewer shots of much higher quality or many shots with a far varied quality range (or score according to Deep Sky Stacker)?

[Startrek (Martin)]

Matthew,
In regards to my 2600MC ,
I ignore scores in DSS when it come to whether a sub is kept or not
I use ASTAP to assess subs and cull satellite trails , cloud , air craft trails and poor Star shape etc.. then once happy, load them into DSS for final registering and stacking
If I used DSS to assess and cull via scoring I’d be throwing out 25% to 50% of my subs for no real reason
I’m venturing into the Mono world myself with the 2600MM, Antlia 2” LRGB and 2” 3nm Ha , Oiii and Sii filters and ZWO 7x2” EFW ( 8” and 10” CF Newts )

I’m adopting the same principles used with my 2600MC to the new 2600MM
Maximise data ( subframes) for each session to improve SNR whether OSC , LRGB or NB

Only my thoughts

Hope other experienced Mono users offer advice too

Cheers
Martin

[Joshua Bunn (Joshua)]

Hi Matt,


It really depends on your goals, not the answer you wanted
For example, if you want better resolution, you would be less forgiving on high FWHM data and the rejection rate would be higher. It also depends on how mach data you have and are likely to collect on the target, you might need to keep more subs to get the S/N up. If its a target that particularly dim, you will need to keep more data.

Image scale also plays a part, there is not much point in being particularly picky by discarding high FWHM data on a relatively wide field target or where you are grossly under sampling.


Josh

[rmuhlack (Richard)]

Ray (Shiraz) made an excellent analysis deep dive into this topic a few years ago. See here: https://www.iceinspace.com.au/forum/...d.php?t=145116