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Old 30-07-2021, 03:52 PM
Gordy
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Reaching faint magnitudes with many subs.

By stacking many subs, does this allow very faint objects to be recorded? In other words, can I use stacking with my slow system (f/7) to image objects that are fainter than the theoretical limit of the scope? Cheers.
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Old 30-07-2021, 03:59 PM
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Stonius (Markus)
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Once you get into photography, the visual magnitude limits no longer apply. If you need to capture dimmer stars you can just keep gathering more data. The limiting factor is noise (and how much time you actually want to spend imaging one object to get tiny incremental improvements).



Cheers,


Markus
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Old 30-07-2021, 04:00 PM
AdamJL
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so long as you're exposing your subs for long enough! Sure.
Exposure time matters here. A fast focal ratio just means you can get there quicker
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Old 30-07-2021, 08:07 PM
RyanJones
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Hi Gordy,

Yes and no. The more subs you take, the more you can subdue the noise in the image which enables you to stretch the faint objects more without stretching the noise with it so thatís the yes. The no is that limiting magnitude is limiting magnitude. The number of subs you take doesnít change that. Magnitude has many limiting factors not least of which is light pollution. An example would be if your sky brightness gives you a limiting magnitude of 15 for example then the size of the scope, the amount of subs or the length of those subs will never be able to reveal anything with a lower brightness than that. Further more to that fact is that in order to seperate the object from the sky brightness there has to be a given difference between the object and the sky so a sky of 15 may mean that only magnitude 13 objects will have enough contrast to be discernible for example.

Hope that clears things up a little

Cheers

Ryan
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Old 30-07-2021, 09:22 PM
Gordy
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Thanks everyone for your responses especially Ryan.

I take it then the main message for me is that a number of short exposures (eg. 50 of 120 seconds) is equivalent to a single exposure of 100 minutes in terms of collecting photons. However, the long exposure will be more affected by sky glow and noise issues with the sensor. Actually it does make sense.
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Old 30-07-2021, 10:03 PM
RyanJones
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Quote:
Originally Posted by Gordy View Post
Thanks everyone for your responses especially Ryan.

I take it then the main message for me is that a number of short exposures (eg. 50 of 120 seconds) is equivalent to a single exposure of 100 minutes in terms of collecting photons. However, the long exposure will be more affected by sky glow and noise issues with the sensor. Actually it does make sense.
Youíre welcome Gordy.

The fact is that there is a seemingly endless number of considerations as to what length subs you take and subsequently the total intergration time you use. There are plenty of guides available to give you a good starting point but from there you will learn what works best with your equipment and also ideal settings to use for certain objects ( some of which will exceed either your equipment or environment) I wonít fill up this space with all of the contributing factors because there are so many to list but also each has a discussion attached as to why various factors have certain effects. I am happy to answer some questions if you have any and would like to PM me.

Cheers

Ryan
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Old 31-07-2021, 02:45 AM
Zuts
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or you could just go bush and find some nice dark sky...
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Old 31-07-2021, 07:42 AM
RyanJones
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or you could just go bush and find some nice dark sky...
With respect, that wonít change the limiting magnitude of your equipment
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