New Script: Calculate Sky Limited Exposure

NKV

PTeam Member
Dec 3, 2008
677
0
blinky said:
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.
 

blinky

Well-known member
Jan 14, 2012
87
1
Ah.... I don't bother with darks as the qhy8 does not need them, or so I was told ???
 

NKV

PTeam Member
Dec 3, 2008
677
0
blinky said:
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.
 

jeffweiss9

Well-known member
Jun 2, 2010
367
1
Sunnyvale, CA
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
 

ecorm

Member
Aug 26, 2017
7
0
What's the difference between Ereadout limit(I) and Ereadout limit(II)?

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

ecorm

Member
Aug 26, 2017
7
0
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).
 

limburg11

Member
Jan 27, 2020
5
0
Hi,

I have some questions concerning bit depth. My ASI294MC Pro has a 14 bit ADC, but the output range in the FITS file is 16 bit, so the output is multiplied by 4. So 65532 in the FITS is really 16383 in the ADC.

1) What do I have to put into ADU Bits and gain? I assume 14, and gain = unity gain = 1 e/ADU.

2) But what about the background image? If it shows a mean of say 800 ADU, this is 16 bit and the real 14 bit value would be 200. How can the script account for that?

Of course I can enter 16 for ADU Bits (and set gain accordingly, unity gain in 14 bit = 0.25 e/ADU in 16 bit), but this would imply I have full 16 bit resolution which is clearly not the case.

Am I missing something? :edit: <= I think I found what I was missing: Intensities in the BG image are normalized to [0, 1], at least in XIFS format. Not sure if this is the case with the imager’s original fits image, though.

Thanks, Bernd
 
Last edited: