[Sticky] Data calibration principles/rules - must read !  

Page 3 / 3 Prev
  RSS

(@cheetah)
White Dwarf Customer
Joined: 10 months  ago
Posts: 17
October 2, 2018 19:04  

If it's non-trivial, perhaps it would be better to create a master list of cameras/sensors and the best way to calibrate for each?  So 1,000 users don't write you, all requesting the same thing.  🙂 

It seems the more I read about calibration images, the more confused I get.  Would be great to get your expert opinion, for (idiot) users like me...

In my case, I use an Zwo Asi1600mc-p.  

 

 

 


ReplyQuote
(@1cm69)
Red Giant Customer
Joined: 11 months  ago
Posts: 50
October 4, 2018 16:59  

Hi Mabula,

I am going to be dipping my toe in to imaging using my ZWOASI120MM-S camera & will be capturing data via SharpCap.

What I have noticed with my test images that I have made is that SharpCap does not write any information to the head of the file i.e. there is no Gain or Temperature etc... the limit seems to be image dimension and exposure length that is written.

Having previously captured data with a DSLR where all the necessary info is written to the file, how does APP cope when this information is lacking?

How does APP know which Darks match which Lights for example if Temperature & Gain is not present in the file?

 

Regards..,

Kirk


ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 2 years  ago
Posts: 1797
October 14, 2018 21:13  
Posted by: Cheetah

If it's non-trivial, perhaps it would be better to create a master list of cameras/sensors and the best way to calibrate for each?  So 1,000 users don't write you, all requesting the same thing.  🙂 

It seems the more I read about calibration images, the more confused I get.  Would be great to get your expert opinion, for (idiot) users like me...

In my case, I use an Zwo Asi1600mc-p.  

Hi @cheetah,

An entire list with camera sensors regarding calibration workflow/paths is not a solution I think for several reasons.

  • camera's of the same model could behave differently, especially CCD camera's.
  • the age of a sensor could be a factor, especially for CCD's
  • some camera models actually have different versions (camera's sometimes get a firmware upgrade which could change amp-glow present or not )
  • the exposure time of your lights could warrent a different workflow, longer exposures could show non-linear problems like amp-glow which then warrents a different workflow.
  • I think it's good that a photographer learns about the sensor in his camera and thinks about how to exploit it 😉 as best as possible
  • probably there are more arguments

So a list would make the illusion that for a fixed camera model the most optimal workflow would always be the same. Unfortunately, it doesn't work like that.

Your camera, the Zwo Asi1600mc-p, has a pretty new CMOS sensor. I have the asi1600mm-c first version myself.

This camera, dus to it's cmos technology seems to give the best calibration in most cases if you use:

  • darks and flats for lights. Try to match the darks for gain and exposure time as good as you can to your lights.
  • flat darks for the flats, again try to match the darkFlats for gain and exposure time as good as you can to your flats.
  • No BIAS ! it seems that bias frames are not very good and this has to do with the sensor readout technology. Omitting bias and using dark flats for the flat calibration is giving better results for most asi-1600 camera's as far as I know.

The asi-1600 does have a little amp-glow, so therefore you don't want to use dark-frame scaling if you can prevent it. Therefore, create darks and flatdarks that properly match the frames to calibrate 😉

Mabula

This post was modified 1 month  ago by Mabula Haverkamp - Admin

Main developer of Astro Pixel Processor and owner of Aries Productions


ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 2 years  ago
Posts: 1797
October 14, 2018 21:19  
Posted by: 1CM69

Hi Mabula,

I am going to be dipping my toe in to imaging using my ZWOASI120MM-S camera & will be capturing data via SharpCap.

What I have noticed with my test images that I have made is that SharpCap does not write any information to the head of the file i.e. there is no Gain or Temperature etc... the limit seems to be image dimension and exposure length that is written.

Having previously captured data with a DSLR where all the necessary info is written to the file, how does APP cope when this information is lacking?

How does APP know which Darks match which Lights for example if Temperature & Gain is not present in the file?

 

Regards..,

Kirk

Hi Kirk @1cm69,

I don't use SharpCap myself, but I have seen some data captured with SharpCap. I think I did see gain and exposure information in the fits header. Maybe ShaprCap was upgraded to have it in the header?

If there is no information, APP will still be able to process it, since APP will automatically use Masters if present allthough gain and exposure time is not known. You will be resposible for knowing how to match it all then if you start to create frames with different exposure times and gain values.

Please let me know if you are able to process the files correctly in APP 😉

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


ReplyQuote
(@cheetah)
White Dwarf Customer
Joined: 10 months  ago
Posts: 17
October 14, 2018 22:21  

This camera, due to it's cmos technology seems to give the best calibration in most cases if you use:

  • darks and flats for lights. Try to match the darks for gain and exposure time as good as you can to your lights.
  • flat darks for the flats, again try to match the darkFlats for gain and exposure time as good as you can to your flats.
  • No BIAS ! it seems that bias frames are not very good and this has to do with the sensor readout technology. Omitting bias and using dark flats for the flat calibration is giving better results for most asi-1600 camera's as far as I know.

 

Thank you!  I'm quite surprised by the -no bias- portion of that.

Do I need to calibrate the flats with the dark flats first...  and THEN load the lights and calibrate with flats and darks?  Or can I simply load everything (lights, darks, dark flats and flats) and have APP do it all in 1 step?

 

 

 


ReplyQuote
(@1cm69)
Red Giant Customer
Joined: 11 months  ago
Posts: 50
October 15, 2018 19:59  

Hi Mabula,

thanks for replying.

I have been playing around with SharpCap & also APT (Astro Photography Tool) saving images as .fits files in both programs.

APT seems to add more info to the header but I think that I have figured out what to do.

Instead of being able to load all raw calibration files and lights in to APP at a single time and letting APP work it's magic with a single button press, it looks as though I need to process each matching batch of calibration files individually to produce their own Masters.

Then I add the Lights along with the newly generated Masters and let APP take over from there.

What I have set up when capturing all RAW data is to add strings to the filenames such as Gain, Exposure Length etc.. just so as I know what matches to what.

This is probably how others do it as well I would assume.

Regards..,

Kirk  😉 


ReplyQuote
Page 3 / 3 Prev
Share: