Old 12-10-2021, 02:01 PM
DIYman (Doug)
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LRGB imaging sequence - Just an idea.

Talking to a astro friend about the best sequence to use when shooting LRGB and we came up with the following process which may interest others.

First, the obvious needs to be mentioned, the best time to image an object is when it is crossing the meridian so that's when the Lum should be taken.

Anyway, here what we are going to be doing where possible (note that last word).

We tend to use 90 sec exposures to avoid over exposed stars and dither for all exposures (I know, I know) and allow 10 secs for the mount to settle after each dither. Adjust the settings to suite your own workflow but I will use ours as an example.

Start exposing when the object is 90 minutes from the meridian.

Red 9 exp

Green 9

Blue 9
Lum 54
Blue 9

Green 9
Red 9

The sequence ends when the object is 90 minutes past the meridian and the process starts for the next next object. (Repeat on another night if more exposures are needed.)

We chose this sequence of the filters as we believe the red filter should be used first as it will be affected least by light passing through the thicker part of the atmosphere. Green follows and then blue which is affected the most by atmospheric scatter. The Lum exposure is the most important and is to be used when the object crosses the meridian.

We realize that flexibility is needed here, such as when the target object is not situated at the optimum altitude or when an object is imaged over more than one nights etc etc.

Anyway, I thought it is an interesting idea and wrote it up while having a beer. Your criticisms and comments please. Cheers.
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Old 12-10-2021, 03:45 PM
kosborn (Kevin)
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That all sounds very sensible. In my case though, I live in a Bortle 4/5 suburban area to the west of a more light polluted urban area. My choice of filters tends to be more influenced by whether I'm pointing east or west, as well as how far off the meridian I am.
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Old 12-10-2021, 07:51 PM
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I always image rgb with blue first and red last past the meridian. As you say red cuts through the thicker atmosphere better than blue and green. Blue also tends to be the most bloated even with decent seeing.

Sometimes its not convenient to wait for an object to be near the zenith given weather, moon and time constraints. Luminance is usually fine in a zone say arbitrarily about 30 degrees on either side of the meridian.

But yes, a good night of good seeing and the object near the meridian you are going to get your best data from luminance.

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Old 13-10-2021, 10:57 PM
DIYman (Doug)
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Thanks Greg and Kevin. Like I said in my post, flexibility is needed, as not everyone can apply the sequence as it has been described. Anyway, others might be in a better position to give it a go. Cheers.
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Old 14-10-2021, 06:27 AM
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The_bluester (Paul)
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I typically just shoot everything I can get as soon as a target is at least 30 degrees in elevation. Usually I am gathering data over several nights and discarding all bar my arbitrary number of best subs on the basis of any with distorted stars through wind gusts or other problems get the flick first, then the ones with the highest HFR get the flick, and if I still have enough, the ones with the brightest background go.

I have some subs shot recently over a night where it was 6-6-6 subs cycling through R-G-B through the night, when I have a chance I should plot the average HFR of each sub of each colour and see if there is a clear trend as the target rose higher.
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