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Individual Frame Times / Atl-Az Mount

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#1 JeffreyHorne

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Posted 19 December 2018 - 12:26 AM

Hello all, and thanks in advance. smile.gif

 

I have a Celestron 8SE with the standard one-arm mount.

 

I'm looking to photograph M42 (Orion Nebula). It will be my first attempt!

 

I'm aware of the field rotation issue that comes along with alt-az mounts, so I'm going to try to get a lot of shorter exposures, and then use DSS for stacking.

 

The setup is:

 

Celestron 8SE

Canon 5D Mk II (modified)

Celestron f/6.3 Reducer

 

I'm planning on locking the mirror for each frame, and taking as many shots as I can get.

 

I think I'm just about ready, but I have a question about exposure times:

 

Given this setup, what is the ideal exposure time before I get blurring/field rotation issues? A best guess is fine, or if there's a tool that can help me calculate this, that would be even better!

 

smile.gif

 

Thanks again!

Jeffrey


Edited by JeffreyHorne, 19 December 2018 - 12:27 AM.


#2 sg6

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Posted 19 December 2018 - 01:47 AM

DSS is not designed for a large series of short duration exposures.

Also the rotation between the first and last exposure is not dependant on the exposure length but on the duration from first to last exposure. Take a 1 hours series of 10 second exposures and the object will have rotated by 15 degrees, take twelve 5 minute exposures and the object will have rotated 15 degrees.

 

What is the maximum rotation between images that DSS can compenstae for and realign? That is what matters. If it is 3 degrees, then you are going to be limited to (3/15)*60 minutes = 12 minutes from first to last in time not in total exposure times as you need to include actions of the DSLR like writing to memory and a bit of spare on each exposure.

 

The requirements for long exposure AP is simple: Good relatively short fast scope and a good solid goto Equitorial mount.



#3 TelescopeGreg

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Posted 19 December 2018 - 01:07 PM

I am going to guess that DSS won't even align the images if the stars show any appreciable tail as a result of the rotation.  It really likes small round stars, so your exposures need to be pretty short.  Crank up the ISO and see what you can get.



#4 Spata

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Posted 19 December 2018 - 07:25 PM

Hello all, and thanks in advance. smile.gif

 

I have a Celestron 8SE with the standard one-arm mount.

 

I'm looking to photograph M42 (Orion Nebula). It will be my first attempt!

 

I'm aware of the field rotation issue that comes along with alt-az mounts, so I'm going to try to get a lot of shorter exposures, and then use DSS for stacking.

 

The setup is:

 

Celestron 8SE

Canon 5D Mk II (modified)

Celestron f/6.3 Reducer

 

I'm planning on locking the mirror for each frame, and taking as many shots as I can get.

 

I think I'm just about ready, but I have a question about exposure times:

 

Given this setup, what is the ideal exposure time before I get blurring/field rotation issues? A best guess is fine, or if there's a tool that can help me calculate this, that would be even better!

 

smile.gif

 

Thanks again!

Jeffrey

I can get 20-25s exposures depending on the wind and they stack fine with DSS.


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