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QHY163M Question about Flats

astrophotography beginner imaging SCT
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#1 smccully

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Posted 16 May 2019 - 03:01 PM

Question about Flats for QHY163M, i know there has been a lot of discussion around this camera. But i am having a hard time getting a grasp on what i need to do to take Flats. At first my understanding is that i would use a lightbox (this one) and point my EdgeHD 11 at it (maybe with a TV Shirt) around it to dim the light. And then i would expose using time and filters as my light frames?

 

Is this accurate or is it different for CMOS cameras vs a CCD? Because when i've read from people asking about taking Flats with this camera or maybe CMOS in general, there seems to be an assumption that the flats only need to be a few seconds long?

 

 

 



#2 elmiko

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Posted 16 May 2019 - 03:15 PM

You need to take a flat to where your histogram peaks at half way. Usually around 30,000 ADU + - 5000.

I take sky flats with a t-shirt tightly over the end of the scope at 1.5 seconds, to get the Histo peak halfway. It will look greyish on your computer screen.

Mike


Edited by elmiko, 16 May 2019 - 03:16 PM.


#3 smccully

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Posted 16 May 2019 - 03:36 PM

Ok, so in Maxim i look at the histogram graph, and i want the X plot to be somewhere in the middle. After that its not important if the exposure is the same as the Light frames.



#4 elmiko

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Posted 16 May 2019 - 03:40 PM

Ok, so in Maxim i look at the histogram graph, and i want the X plot to be somewhere in the middle. After that its not important if the exposure is the same as the Light frames.

That is correct sir. 

Darks have to be the same as the lights as far as temperature and length. And gain settings.

I take 30 flats and calibrate them along with my bias frames.

What do you use for processing?



#5 smccully

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Posted 16 May 2019 - 04:12 PM

I am going with Pixinsight (trial), and walking through the process now. I have captured about 25 or so frames of m101.

 

I am currently taking additional Darks, and then will start on capturing flats. 


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#6 elmiko

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Posted 16 May 2019 - 05:34 PM

The batch PreProcessing script in Pixinsite works really well. Pretty straight forward. Load your lights your darks your flats and bias. Pick the appropriate rejection algorithm. I use Linear fit clipping, seems to work well for me. I usually have between 40 and 60 lights. Leave everything at default. Works reliable. I found that using the correct flats makes the biggest difference in calibration.

Mike


Edited by elmiko, 16 May 2019 - 05:38 PM.



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