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Utilizing Darks Library

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#1 birddog99

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Posted 03 April 2020 - 11:21 PM

Just want to make sure I understand how to properly use dark libraries.

 

I use APT for capture and the camera is an ASI533MC Pro

 

Please correct me if I'm wrong.

 

Step 1 - Take dark frames consisting of groups of specific exposure times using the same temperature, i.e -10. i.e 30sec, 60sec, 90sec, 120sec, and on. 

 

Step 2 - Calibrate and Integrate each group to create a master dark for each group. ( i use pixinsight )

 

I am using down time due to bad weather to create these libraries. I am going to get 3 hours of integration time for each group

 

Here are my questions :

 

     If, for example, I have an imaging session where I was only able to get 2 hours integration time on a particular target, is it ok to use the master dark I created with the 3 hour integration time, or would I need to select the number of darks that would be appropriate for 2 hours integration time and recalibrate/reintegrate to create a new master dark. I try to use a quantity of 50% darks compared to the number of light frames taken. i.e 100 lights/50 darks.

 

     If in the case it will be correct to reintegrate/recalibrate for the 2 hour session, is there any degradation of the image files if I copy those files into another directory to be recalibrated.

 

     Is there a specific amount of time I can continue to use a specific master dark file, or will I need to refresh my libraries occasionally by taking a fresh set of darks.

 

I hope I'm making sense with these questions. If it sounds like I have a handle on this procedure, great. But please set me straight if I'm wrong. Thanks for the replies in advance

 

     



#2 richorn

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Posted 04 April 2020 - 02:29 AM

The darks have nothing to do with integration time, just image time.

 

To that end, take 50 darks of each exposure time, gain, and temp you plan on using.

 

i.e.  

 

50x 300 sec at gain 200 offset 50 temp -10

50x 300 sec at gain 200 offset 50 temp -15

50x 300 sec at gain 200 offset 50 temp -20

50x 300 sec at gain 139 offset 50 temp -10

50x 300 sec at gain 139 offset 50 temp -15

50x 300 sec at gain 139 offset 50 temp -20

 

etcetera, etcetera

 

When you are processing, you are going to use a master dark that matches the exposure time, gain and offset, and temp of the lights.  The number of lights used to crate the integration is unimportant in this regard.

 

Did any of that make sense?  lol it is getting late...  In my case, I only use 4 different gain settings, and 2 different temperature settings.  -20 for winter, -15 for summer, gains of 0, 76, 139 (unity) and 200.  Of course, the new 533 has different properties than the 1600, so your settings will be different across the board I would think.


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#3 nimitz69

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Posted 04 April 2020 - 11:47 AM

unless you plan to do a lot of HDR imaging, NB and/or image at a wide range of locations where LP varies considerably you really don't need very many different sub exposure times.  i think you'll  find most experienced imagers use only a couple of times and maybe one or two temps. it makes things much simpler and the focus should be on total integration time which trumps everything else.

 

I use only one temp (-10 deg) and a default sub length of 2 mins unless I'm doing NB or M42 - just something to onsider



#4 jemarcks

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Posted 19 April 2020 - 10:14 AM

I also bought a asi533mc-Pro and it arrived a couple days ago.  tonight is going to be clear skys and I get to try it out.

I got all the software updated on my laptop and played with the camera to test it out.

I use APT for imaging and have the latest version 3.84 installed.  

While I wait for the clouds to clear today I wanted to get my darks done.

In APT I can enter a target temperature (45C) or a delta from ambient (-15C).  

 

Should I shoot with target temperatures or deltas?  I am new to asi cameras and only started in AP 5 months ago.

 

thanks!



#5 Madratter

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Posted 19 April 2020 - 10:23 AM

Use a target temperature, that will be easier to match up with dark libraries, etc. If you were to use delta from ambient, a dark of -15 might be a very poor match for a light of -15 because it is the absolute temperatures that must match.



#6 copper280z

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Posted 19 April 2020 - 10:44 AM

I'm new at this, but I use one gain, one offset, one (absolute) temp, and have a variety of exposure times from 15s to 180s. I used 100 frames for each master, and did a median combine.

Edited by copper280z, 19 April 2020 - 10:45 AM.


#7 jemarcks

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Posted 21 April 2020 - 01:05 PM

What gain is everyone using for their asi533mc pro?

I tried unity gain and when I shot some images, they were all dark no mater the exposure length.  When I stretched the data (in APT) i could see a few dim stars.  Is this normal?  Am I doing this wrong?  

 

thanks!




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