Newbie - calibration issues - needs some advice

[ribuck]

Hi All,

This is my first post, so please be gentle on a newbie :-)

I'm new to pixisnight and i'm having a few teething problems with initial calibration / Integration and need some advice.   I'm finding that after calibration my lights look like they haven't had flats appplied, as they are very foggy looking.  During the calibration process i noticed that  i got a warning on 2 of my files saying "Warning : No correlation between Master Dark & Master Flat"

So i have all my files and i my work flow was as follows :-  Not sure where i am going wrong.

Create Calibration Masters
1)generate master bias  - average, no normalization, weights - dont care, evaluate noise unticked, Winsorized Sigma Clipping, sigma Low = 4, High = 3
2) generate master dark -  Sam settings as above.
3) Generate master flat -  1st - calibrate flats, subracting dark & bias
                                          2nd - Intrgrate flats with Percentil clipping and Equalize flux

Calibrate Lights
1) Run image calibration for lights, add in master dark, bias,  flat ensuring calibrate options are ticked along with optimze for darks
2) Run Star alignment on newly calibrated images
3) Integrate new staraligned calibrated images  - Winsorized sigma clipping, scale + zero Offset,  sighma Low 4, Sigma high = 3


Any help would be greatly appreciated.

Many Thanks,
Rich.

[pfile]

do you have darks that match the flat duration? if not, and the flats are short, this could be a problem. if your flats are short (<10s) i'd just calibrate them with the master bias, as long as you are using a cooled CCD.

rob

[ribuck]

Hi rob,

I dont have matching darks for the flats, as all my darks are 300, 600, or 1200 second in duration and my flats for the different filters range from 0.16-22 seconds.

So my Lum is 0.16s for the flat, so do i need to do a matching  0.16s dark ?

 

[jkmorse]

Rich,

I am betting you are using MaximDL as your capture software, am I right?  If so I have some ideas since this is a problem I have run into any number of times.

Jim

[jkmorse]

Rich,

Even if you are not using MaximDL, one thing to try is to NOT use a bias frame when you calibrate your lights, just use a master dark and a master flat.  Also try without ticking the calibrate and optimize boxes.  It should work. 

You know something is amiss when you get that foggy look.  It means things got blown out and something is truncating data, usually where data is being read as signed integer data and you are losing all the negative values.

Jim 

[ribuck]

Hi Jim,

I dont use maxim at the moment, i'm using Sequence Generator Pro for my capture.  I'll try recreating my master dark, and try just doing the bias subtraction on the master as you suggest.

will report back soon.

[ribuck]

Hi Rob,

I tried as you suggested and no joy.  I'm going to post up my masters Dark, Flat & Bias with a single light frame and see if anyone can try processing it from their end and get a different result.



This is the log, from processing a single file

ImageCalibration: Global context

Loading master calibration frames:
Loading calibration frame image:
C:/Users/Rich/Google Drive/CCD_Images/Calibration/Master/Master_Dark_BiasCal_600s-25.fit
Reading FITS: 32-bit floating point, 1 channel(s), 3326x2504 pixels: done
Loading calibration frame image:
C:/Users/Rich/Google Drive/CCD_Images/Calibration/Master/Master_Flat_Lum_-25.fit
Reading FITS: 32-bit floating point, 1 channel(s), 3326x2504 pixels: done

Calibrating master flat frame ...
Optimizing master dark frame:
Bracketing...
Optimizing...
k0 = 0.000
** Warning: No correlation between the master dark and master flat frames (channel 0).
Computing master flat scaling factors ...
s0 = 0.551258

Calibration of 1 target frames:
* Using 1 worker threads

Calibrating target frame 1 of 1
Loading target frame:
C:/Users/Rich/Google Drive/CCD_Images/Light/M33/Light/M33_600sec_1x1_L__frame1_-25.0C.fit
Reading FITS: 16-bit integers, 1 channel(s), 3326x2504 pixels: done

Writing output file: C:/Users/Rich/Google Drive/CCD_Images/Test/M33_600sec_1x1_L__frame1_-25.0C_c.fit
Dark scaling factors:
k0 = 0.859
Writing FITS image: 32-bit floating point, 1 channel(s), 3326x2504 pixels: done

===== ImageCalibration: 1 succeeded, 0 failed, 0 skipped =====
3.670 s

 

[jkmorse]

Yeah, post them so people can take a look and someone will definitely be able to help.  Without seeing the images, its just guesswork.

Best,

Jim

[ribuck]

Jim,

Here are my files :

Integrated Light (10x600s)   :  https://drive.google.com/file/d/0B1K-EA9ZuRxzMUdqLUhkTXBhY28/view?usp=sharing

Master bias :   https://drive.google.com/file/d/0B1K-EA9ZuRxzU1Y3OXRDak10RDA/view?usp=sharing

Master Dark :  https://drive.google.com/file/d/0B1K-EA9ZuRxzRkgycUhpdUZ5dzA/view?usp=sharing

Master Flat :   https://drive.google.com/file/d/0B1K-EA9ZuRxzMmVFLXJYWVpiZTQ/view?usp=sharing


Uncalibrated Light : https://drive.google.com/file/d/0B1K-EA9ZuRxzTFdnZnFIZ2ZsYUE/view?usp=sharing
Hopefully someone can take a look at these and give me an idea of what's going on, or not going on as the case might be.

[pfile]

master flat permissions are preventing download…

rob

[ribuck]

Hi Rob,

thanks for the heads up, i've updated the original link.

Rich.

[pfile]

so the master dark was made from uncalibrated dark subs?

the strange thing here is that the master dark's average values are very similar to the bias frame.

or was the master dark you posted created with calibrated dark subs?

rob

[ribuck]

Hi Rob,

I can't remember now if the master dark was calibrated or not.   I'll redo my master darks tonight and ensure they aren't calibrated and then post them up.

Rich.

[MikeOates]

Hi Rich,

Please take a look at this post, where Juan gives the answer:

http://pixinsight.com/forum/index.php?topic=6797.msg46103#msg46103

Basically, just ignor the error message, or don't use darks. Some cameras have so little noise it's not needed, they are certainly not needed for short duration flats, most of the noise in those can be removed using bias only.

Mike

[ribuck]

Hi Mike,

I'll try redoing my flats and just subtract the bias and nothing else and see how i get on.  I'll also redo my master dark and make sure the optimize setting is un-ticked.

Just a steep learning curve especially when i'm stumbling straight out of the starting blocks.

Rich.