Author Topic: New Script: Calculate Sky Limited Exposure  (Read 31883 times)

Offline NKV

  • PTeam Member
  • PixInsight Guru
  • ****
  • Posts: 676
    • View Profile
Re: New Script: Calculate Sky Limited Exposure
« Reply #60 on: 2012 September 30 23:31:35 »
So..... Do I just use a preview from a single un-debayered sub and unstretched sub?  If I do that I get a max exposure of around 2.5mins which is not good :-[  Also how/what is the pedestal value?
I have been taking 600s images in the hope that I can bring out some faint detail but it now seems that 2mins is it and any more is pointless :-\
Deduct a 600s Dark frame from the Light and try. ;)

PS some pop-up notes or separate selector for DarkFrame will very useful.

Offline blinky

  • Member
  • *
  • Posts: 59
    • View Profile
Re: New Script: Calculate Sky Limited Exposure
« Reply #61 on: 2012 October 01 03:19:34 »
Ah.... I don't bother with darks as the qhy8 does not need them, or so I was told ???

Offline NKV

  • PTeam Member
  • PixInsight Guru
  • ****
  • Posts: 676
    • View Profile
Re: New Script: Calculate Sky Limited Exposure
« Reply #62 on: 2012 October 01 03:27:36 »
Ah.... I don't bother with darks as the qhy8 does not need them, or so I was told ???
Anyway you must subtract Dark for correct calculation. But, if your camera have zero dark current, you can subtract bias frame.

Offline jeffweiss9

  • PixInsight Old Hand
  • ****
  • Posts: 333
    • View Profile
Re: New Script: Calculate Sky Limited Exposure
« Reply #63 on: 2012 November 04 17:49:48 »
It seems most of the time I try this, the process console shows the following error:
" line 26: TypeError: img is undefined"
I'm just reading in a standard CCDSoft v5 FIT file so why does it think the image is undefined?
In playing around with it, I once got an actual result, although I don't believe the 2 minute subs that it was telling me I needed for an extremely dark site and 8 e- readout noise (Austel model, the other models gave 30sec sky-limited exposure).

Also, I gather it needs a dark subtracted image, which this wasn't.  Can the script just ask for a master dark and do the subtraction?  Dark subtracted subs are just not something laying around in the PI calibration process (calibrated frames are but they have flats divided out) and it would save some Pixelmath. In any case, I get the same result as described above if I do a Pixelmath dark subtraction first. 

I'm guessing its not finding something in the FITS header, but if PI is happy, why isn't the script happy?  The script asks you to enter the exposure time of the image.

Thanks for your help.
-Jeff
APM LZOS 130/780 f/6 LW CNC II APO, Riccardi 1.0 FF or 0.75 FF/FR, Tak EM-200 Temma2, FLI Microline ML-16200, Astrodon E Gen 2 filters and 5nm Ha, Orion 50mm Guider & SSAG

Offline jeffweiss9

  • PixInsight Old Hand
  • ****
  • Posts: 333
    • View Profile
Re: New Script: Calculate Sky Limited Exposure
« Reply #64 on: 2012 November 20 21:11:51 »
Note, giving it a preview, rather than the image itself, seems to avoid this problem.
-Jeff
APM LZOS 130/780 f/6 LW CNC II APO, Riccardi 1.0 FF or 0.75 FF/FR, Tak EM-200 Temma2, FLI Microline ML-16200, Astrodon E Gen 2 filters and 5nm Ha, Orion 50mm Guider & SSAG

Offline Robert Q. Kimball

  • Newcomer
  • Posts: 30
    • View Profile
Re: New Script: Calculate Sky Limited Exposure
« Reply #65 on: 2014 July 31 14:18:09 »
I love this script.  Can I assume that with my Atik 383L (8300 chip) I can use the SBIG 8300 selection?

Thank

Offline ecorm

  • Newcomer
  • Posts: 2
    • View Profile
Re: New Script: Calculate Sky Limited Exposure
« Reply #66 on: 2019 March 04 19:16:29 »
What's the difference between Ereadout limit(I) and Ereadout limit(II)?

I see that Dark Noise affects II, but not I.

Offline ecorm

  • Newcomer
  • Posts: 2
    • View Profile
Re: New Script: Calculate Sky Limited Exposure
« Reply #67 on: 2019 March 04 19:49:30 »
By inspecting the script's Javascript code, I figured out that Ereadout limit (I) comes from equation (3) in John C. Smith's paper (which I had to retrieve using the Internet Wayback Machine).

Ereadout limit (II) comes from Chuck Anstey's article, equation (9).