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Exposures time of Lights

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#1 Gbarr56

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Posted 11 June 2021 - 09:28 AM

I currently have been shooting 5 minute subs with success. Any benefit to trying for longer exposures? My tracking is not bad on my 1230mm Fl scope.

Thanks in advance.


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#2 kathyastro

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Posted 11 June 2021 - 09:49 AM

Longer exposures are only needed if your targets are dim enough that they are buried in the noise, and then only if your skies are dark enough to avoid clipping highlights.  If you are getting decent detail in the dimmer parts of your targets, then longer subs just give Murphy more time to make things go wrong.  Total integration time is more important.


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#3 Gbarr56

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Posted 11 June 2021 - 09:55 AM

Longer exposures are only needed if your targets are dim enough that they are buried in the noise, and then only if your skies are dark enough to avoid clipping highlights. If you are getting decent detail in the dimmer parts of your targets, then longer subs just give Murphy more time to make things go wrong. Total integration time is more important.


Thanks for the info. How can you tell if a target is dim or not in your planning? AND, on another note, how can you know if better to shoot LRGB vs SHaO? If I pick a Nebula, do I assume I should just shoot SHaO and L for detail? I was looking for something like….pick a nebula target, see what filters are best to shoot, and see brightness level to make a determination of exposure. Tall order but is there any site like that, that answers those questions in planning?


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#4 kathyastro

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Posted 11 June 2021 - 10:13 AM

Astrobin is a pretty good site for target planning.  You can see the details of how other people shoot targets.  You can also cut and paste target information into SGP if you use that software.

 

For brightness information, the parameter you need to look for is magnitudes per square arcsecond.  Overall magnitude is easier to find, but not helpful.

 

Narrowband filters (SHO) are good for emission nebulae.  Broadband (LRGB) are good for reflection nebulae, galaxies, and star clusters, as well as for emission nebulae.  In other words, you won't go wrong collecting broadband data on any target.


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#5 Gbarr56

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Posted 11 June 2021 - 10:16 AM

Astrobin is a pretty good site for target planning. You can see the details of how other people shoot targets. You can also cut and paste target information into SGP if you use that software.

For brightness information, the parameter you need to look for is magnitudes per square arcsecond. Overall magnitude is easier to find, but not helpful.

Narrowband filters (SHO) are good for emission nebulae. Broadband (LRGB) are good for reflection nebulae, galaxies, and star clusters, as well as for emission nebulae. In other words, you won't go wrong collecting broadband data on any target.


Thanks so much Kathy for your insight. I use SGPro so will use that feature. Great info!


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#6 Peregrinatum

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Posted 11 June 2021 - 10:17 AM

I currently have been shooting 5 minute subs with success. Any benefit to trying for longer exposures? My tracking is not bad on my 1230mm Fl scope.

Thanks in advance.


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theoretically you want to shoot the longest exposure you can if the object or star field would not get over saturated, 1 single 25 hour image LOL!

 

however, there gets to be a practical maximum in terms of guiding, and the potential pain of tossing out a sub because of a satellite trail or a gust of wind came in etc... it wouldn't be so painful to have to toss a 10' sub but it would really hurt to have to toss a 30' sub... see what I mean?

 

personally I have set a 10' maximum and that is a balance between my pain threshold and the capabilities of my equipment


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#7 Gbarr56

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Posted 11 June 2021 - 10:22 AM

theoretically you want to shoot the longest exposure you can if the object or star field would not get over saturated, 1 single 25 hour image LOL!

however, there gets to be a practical maximum in terms of guiding, and the potential pain of tossing out a sub because of a satellite trail or a gust of wind came in etc... it wouldn't be so painful to have to toss a 10' sub but it would really hurt to have to toss a 30' sub... see what I mean?

personally I have set a 10' maximum and that is a balance between my pain threshold and the capabilities of my equipment


Thanks for that info. If there is a satellite trail, you always throw out? The preprocessing can’t make use of that data if there is this trail?


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#8 Peregrinatum

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Posted 11 June 2021 - 10:35 AM

Thanks for that info. If there is a satellite trail, you always throw out? The preprocessing can’t make use of that data if there is this trail?


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I only toss out a satellite trail if it is going right through a critical part of the target, otherwise I keep it and let the integration rejection algorithms manage it


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#9 Gbarr56

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Posted 11 June 2021 - 10:39 AM

I only toss out a satellite trail if it is going right through a critical part of the target, otherwise I keep it and let the integration rejection algorithms manage it

Ok, thanks



#10 rgsalinger

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Posted 11 June 2021 - 11:07 AM

If you were to expose for 24 hours all that you would get, unless your scope is on the moon, is a completely saturated image - 64K ADU - across the frame. That's much truer today with modern CMOS cameras that have much higher QE. Once you saturate the chip, it's impossible to get the information back. I know that the 24 hour example was just a figure of speech but there's a practical limit in many suburban locations with regards to how long you can expose before the system saturates. That's why narrow band imaging is so popular in cities these days. 

 

Rgrds-Ross


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#11 philinbris

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Posted 11 June 2021 - 06:56 PM

I like Kathy's reply.

Also following this U Tube from Dr Robin Glover (SharpCap guy): https://www.youtube....h?v=3RH93UvP358

Around the 40 min mark he discusses that short subs (say 10-45 sec) is about all you need for a cooled DSO camera.

If you look at Steven Bellavia's Spreadsheet for ZWO cams (mine is 533, he has other spreadsheets for other cams in ZWO range) that seems to support the shorter 45 sec subs: https://www.cloudyni...-the-zwo-asi533.

I have done some great shots of targets using as little as 100 10 sec subs with cam cooled to -5 degc.

So I support the shorter subs theory but more of them - so total integration time is better even if its lots of huge files I am happy to wait.

Cheers


Edited by philinbris, 11 June 2021 - 06:57 PM.

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#12 Gbarr56

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Posted 12 June 2021 - 07:39 AM

I like Kathy's reply.
Also following this U Tube from Dr Robin Glover (SharpCap guy): https://www.youtube....h?v=3RH93UvP358
Around the 40 min mark he discusses that short subs (say 10-45 sec) is about all you need for a cooled DSO camera.
If you look at Steven Bellavia's Spreadsheet for ZWO cams (mine is 533, he has other spreadsheets for other cams in ZWO range) that seems to support the shorter 45 sec subs: https://www.cloudyni...-the-zwo-asi533.
I have done some great shots of targets using as little as 100 10 sec subs with cam cooled to -5 degc.
So I support the shorter subs theory but more of them - so total integration time is better even if its lots of huge files I am happy to wait.
Cheers


Thanks for this information. Food for thought. I see an experiment comparison coming. Now, I just need to learn Pixinsight.


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#13 Gbarr56

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Posted 12 June 2021 - 11:56 AM

I like Kathy's reply.
Also following this U Tube from Dr Robin Glover (SharpCap guy): https://www.youtube....h?v=3RH93UvP358
Around the 40 min mark he discusses that short subs (say 10-45 sec) is about all you need for a cooled DSO camera.
If you look at Steven Bellavia's Spreadsheet for ZWO cams (mine is 533, he has other spreadsheets for other cams in ZWO range) that seems to support the shorter 45 sec subs: https://www.cloudyni...-the-zwo-asi533.
I have done some great shots of targets using as little as 100 10 sec subs with cam cooled to -5 degc.
So I support the shorter subs theory but more of them - so total integration time is better even if its lots of huge files I am happy to wait.
Cheers


Great talk. I happen to have the noisy 8300 ccd chip in my camera he referred to so looks like 240 seconds for me. Thanks again.


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#14 Bill001

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Posted 12 June 2021 - 12:09 PM

I currently have been shooting 5 minute subs with success. Any benefit to trying for longer exposures? My tracking is not bad on my 1230mm Fl scope.

Thanks in advance.


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I do shoot at 10 minutes or more on a F10 at 2032mm, i have pristine skies and shoot at gain 0. My images are very quiet. I shoot a variety of test images and measure the test subs in PixInsight to examine the exposure before I pick an exposure time. I look at the stars to see if any are blowing out. My goal is to use effectively utilize the full well depth of my 16 bit camera particularly on faint targets.

 

My subs range from 5 min to 10 commonly and for filtered targets I’d consider going longer.



#15 philinbris

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Posted 12 June 2021 - 07:22 PM

Yeah, it seems to all come down to noise and external light pollution.




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