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Nina optimal exposure calculator

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4 replies to this topic

#1 Splurk

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Posted 04 August 2021 - 05:13 AM

Hi all. Being new to astrophotography (9 months) I have done a lot of reading on hear about how to judge the best exposure time. I have read the Deep Sky Imaging Primer and been on several websites as mentioned in other posts.
So since I got my Asi294mm, filters etc I have been taking subs in Ha for example in 5,10,15 & 20 minute exposures. And I decided to try the calculator. It said 90 seconds. And for each different filter it had a different time but always the same MAD:20. And I remembering reading on a website that there is a curve for snr ratio and after a time it's pointless exposing longer as the noise is already swamped for that exposure and any longer you just reduce dynamic range by maxing out the ADUs with very little extra snr.
Of course, being in a Bortle 1 means less sky glow and longer exposures and in bortle 8 (me) then go with the calc?
Anyone else use the calculator and follow the recommended times?
Mark.

#2 Sean1980

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Posted 04 August 2021 - 06:28 AM

I use the calculator, but mostly for LRGB. For narrowband I just stick with 5 minutes and as much time as possible on target. I am in bortle 8/9 so I get recommendations of 8s on L and 16 to 20 for RGB. So I usually just stick with 15s L and 30s for RGB. Try to get about 10 hrs L and 3 hrs each RGB. If you want to do the math it’s a whole lot of files to stack

#3 ghilios

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Posted 04 August 2021 - 09:11 AM

You may want to consider using Sharpcap if you do alot of short exposures due to being in B8, B9+ skies. You can use live stacking to create 1-5 minutes stacks of short exposures which you can then process more normally. Many members of the astronomy club in New York City take this approach when imaging from rooftops within the city.


Edited by ghilios, 04 August 2021 - 09:11 AM.


#4 Splurk

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Posted 04 August 2021 - 09:28 PM

I use the calculator, but mostly for LRGB. For narrowband I just stick with 5 minutes and as much time as possible on target. I am in bortle 8/9 so I get recommendations of 8s on L and 16 to 20 for RGB. So I usually just stick with 15s L and 30s for RGB. Try to get about 10 hrs L and 3 hrs each RGB. If you want to do the math it’s a whole lot of files to stack


Thanks. I did some different exposure lengths of 3,5,10 & 20 mins with Ha and not much changes in the greater times other than more saturated pixels so I will give it a go on my current object.

Edited by Splurk, 04 August 2021 - 09:31 PM.


#5 Splurk

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Posted 04 August 2021 - 09:40 PM

You may want to consider using Sharpcap if you do alot of short exposures due to being in B8, B9+ skies. You can use live stacking to create 1-5 minutes stacks of short exposures which you can then process more normally. Many members of the astronomy club in New York City take this approach when imaging from rooftops within the city.


I have the free version of sharpcap but only used it to check the sensor. Dss also has live stacking but never tried it.
I think for me just taking 300 subs and checking them to weed out the rubbish is better. Live stacking might stack bad subs and ruin a stack.
I have a reasonably fast PC so it only takes 10-15 mins to stack 300 subs.
Ive just completed M20 with 3 min luminance and 10 min NB subs and scrapped quite a few due to clouds and wind so my 12 hours of data took around 15 hours over 5 nights.
I think with shorter sub times not as much time will be wasted (fingers crossed).


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