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Time length for Flats & Darks

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#1 7mag

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Posted 23 January 2020 - 09:43 AM

Newbie question and I'm sure it's probably been asked before, but I cannot find a definitive answer.

 

I only have a remote shutter release for my DSLR and using a stop watch for how long I want to take the shot.

 

To take dark and lights, do the times have to to exact for each shot? 

 

If the shots are 1 sec or 1/2 sec off of each other is that ok and will you still be able to stack/ process the images, etc correctly if the times are slightly off ? 

 

Thank you for any responses on this.



#2 Dynan

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Posted 23 January 2020 - 09:54 AM

You need to be precise with this. I have one of these for my T5:

 

https://www.amazon.c...0NsaWNrPXRydWU=

 

Your temperature will be deviating with an uncooled camera also, so do the best you can. Both are important to get as close as possible for best results. But, as the old racing saying goes:

"Run what ya' brung!"


Edited by Dynan, 23 January 2020 - 09:54 AM.

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#3 Michael Covington

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Posted 23 January 2020 - 10:00 AM

A difference of a few percent (e.g., 30 vs 32 seconds) is not going to interfere with calibration, although some software may refuse to do it because of the apparent mismatch.

Darks should be the same exposure time as deep-sky image exposures.

Flats are usually short (done with the shutter) and it is no problem to make flat darks that are the same length.  



#4 7mag

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Posted 23 January 2020 - 10:13 AM

My apologies, I did mean dark and light. Trying to work and ask questions at the same time.  Fingers typing got ahead of the brain.

 

I'll try as best as possible with what I have.  And yes, an intervalometer is on the future to buy list. 

 

Thank you for the responses.



#5 Stargezzer

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Posted 23 January 2020 - 11:04 AM

Depending on your camera you may be able to use a free camera control program such as DigiCam to run your session. I use a Nikon D5300 and the DigiCam program works for me. BYNikon or BYEOS has more features and both are very popular. Try the DigiCam out before you buy a intervalometer.


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#6 han.k

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Posted 23 January 2020 - 11:38 AM

The dark are a combination a fixed value and a component which increases slowly over time. A few seconds longer or shorter doesn't make much difference.

 

You can always test it. Take a dark of 1 second and one of 10 seconds and subtract.

 

You should try to make the images and darks at the same temperature. The same for the flats and the bias=flat darks. The temperature of the images & darks should be at temperature A and flats & bias should be at temperature B. Temperature A and B can be different.

 

Han



#7 bobzeq25

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Posted 23 January 2020 - 12:49 PM

The dark are a combination a fixed value and a component which increases slowly over time. A few seconds longer or shorter doesn't make much difference.

 

You can always test it. Take a dark of 1 second and one of 10 seconds and subtract.

 

You should try to make the images and darks at the same temperature. The same for the flats and the bias=flat darks. The temperature of the images & darks should be at temperature A and flats & bias should be at temperature B. Temperature A and B can be different.

 

Han

Pretty much agree, but A is important, B not so much.  Bias and flats on a DSLR are short enough that thermal noise is not a significant problem for a beginner.

 

If purchasing an intervalometer is a barrier, you're going to find a lot of them ahead.  <smile>
 


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#8 Kendahl

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Posted 23 January 2020 - 02:33 PM

Darks should match lights in ISO, duration and sensor temperature. Since durations are several minutes for DSO photography, a few seconds error isn't important.

 

Controlling duration with a cable release and a stopwatch is a major PITA. If you don't want to drag a laptop computer into the field, I recommend you buy an intervalometer.



#9 nimitz69

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Posted 24 January 2020 - 11:59 AM

what stacking program are you using?  When I was using DSS it would not stack lights and darks that were not the same exposure time - maybe there is a way to do it?

 

as Bobzeq25 says .... if $39 is a barrier to getting a basic piece of equipment you are probably going to be in for quite a few more ..... dalek12.gif

 

AP is not for the financially faint of heart ....



#10 7mag

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Posted 24 January 2020 - 05:38 PM

It wasn't actually that bad using the remote shutter release.  There was a counter on the dslr screen that made it easy.  Just had to sit and wait and watch the counter.  I will be getting an intervalometer.  Just been putting pieces of the project together rather slowly.

 

That was actually my next question.  What is the most recommended stacking program.

 

I do appreciate all of the responses.  Thank you.




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