Correcting lens aberrations

General discussion about StarTools.

Correcting lens aberrations

Postby DorsetBlue » Thu Sep 08, 2016 1:50 pm

Hi all,

New user here. Just paid for the full version after ST did such an excellent job on some Widefield DSLR images (using the Canon kit lens) I had taken during my recent holiday to Spain.

Now this question is due to another dataset I took during the holiday. These were 30x30s lights I took of M31 using my Tamron zoom lens at 200mm. Although they are (I think anyway) reasonably in focus, I kept the aperture at the most open setting and this seems to have caused some rather nasty aberrations of the stars surrounding M31 (I think they are astigmatism lens aberrations, anyway the stars have turned into bloated triangles). I have processed the dataset twice in DSS and I just seem to end up with a background that overcomes the detail that I seem to have in M31, i'm guessing because DSS cannot find these stars due to the aberrations.

Would it be better to convert these 30 frames into TIFFs/FITS and then clean them up with the Repair module in ST before stacking them in DSS?
DorsetBlue
 
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Re: Correcting lens aberrations

Postby DorsetBlue » Sun Sep 11, 2016 5:01 pm

I decided to try again and use ST on the DSS FITS image and I got the following. I think it is about right for the quality of the data in the FITS image but I would be interested if anyone can get better from that data and how they did it:

M31.jpeg
M31.jpeg (171.13 KiB) Viewed 343 times


For info I did the following in ST:

AutoDev
Crop artifacts
Bin 50%
Wipe - Vignetting - Default
AutoDev - POI rectangle over M31 core and M110
Life - Star Mask - Isolate
HDR - Optimise - Default
Colour - Default + Green to Yellow
Stop Tracking - Denoise (Default)
Repair - Star Mask - Warp (Default)

Original DSS FITS here: https://drive.google.com/open?id=0B7ZyHcV3W3qcYVRFWUlFb29aT0U
DorsetBlue
 
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Re: Correcting lens aberrations

Postby almcl » Mon Sep 12, 2016 7:25 am

Had a very quick go. See what you think? If of interest I'll post the workflow (possibly not till this evening - got to go to work).
M31.jpg
M31.jpg (133.6 KiB) Viewed 335 times
Skywatcher 200P with an astro modded Canon 700d, cls ccd filter, field flattener, guided by QHY 5Lm, PHD2
almcl
 
Posts: 68
Joined: Wed Jan 21, 2015 7:15 pm
Location: Shropshire. UK

Re: Correcting lens aberrations

Postby DorsetBlue » Mon Sep 12, 2016 7:56 am

Wow, yes please! That looks really good (I am at work now too, so won't be able to play more until this evening either :) ).
DorsetBlue
 
Posts: 4
Joined: Thu Sep 08, 2016 10:43 am

Re: Correcting lens aberrations

Postby almcl » Mon Sep 12, 2016 4:52 pm

I rushed this so didn't do HDR and contrast and probably over cooked the the noise reduction. Also, have a look at Ivo's tutorial on background extraction here:

http://forum.startools.org/viewtopic.php?f=7&t=244

I think working separately on the stars could yield dividends.

Another thought is that it might still be worth taking some flats, even now, partuclalarly if you can accurately produce the zoom lens focal length, and then re-stacking. It will help with the vignetting. I didn't see any dust bunnies (there may be some) but if there are they can be masked out of the wipe separately.

OK, here we go:

.

File loaded [E:\Astronomy\someone elses files\M31 - Rational Mk3.FTS].
---
--- Bin
Parameter [Scale] set to [(scale/noise reduction 35.38%)/(798.89%)/(+3.00 bits)]

--- Auto Develop
Parameter [Ignore Fine Detail <] set to [Off]
Parameter [Outside ROI Influence] set to [15 %]

--- Crop
Parameter [X1] set to [6 pixels]
Parameter [Y1] set to [4 pixels]
Parameter [X2] set to [1837 pixels (-5)]
Parameter [Y2] set to [1225 pixels (-4)]

--- Wipe
Defaults except
Parameter [Precision] set to [128 x 128 pixels]

--- Develop
Defaults except
Parameter [Digital Development] set to [94.00 %]
Parameter [Dark Anomaly Filter] set to [11.1 pixels]

Another crop to reduce some residual Vignetting
--- Crop
Parameter [X1] set to [220 pixels]
Parameter [Y1] set to [176 pixels]
Parameter [X2] set to [1631 pixels (-200)]
Parameter [Y2] set to [1157 pixels (-64)]

--- Deconvolution
Defaults except
Parameter [Radius] set to [1.4 pixels]

--- Life
Isolate
Defaults except
Parameter [Strength] set to [204 %]

--- Color
Defaults

--- Wavelet De-Noise
Defaults except
Parameter [Grain Size] set to [30.9 pixels]

--- Star mask then

--- Repair
Defaults except
Parameter [Algorithm] set to [Redistribute, Core Is Avg Location]

--- Magic
Defaults

--- Develop
Defaults except

Parameter [Gamma] set to [0.83]
Parameter [Dark Anomaly Filter] set to [10.9 pixels]

HTH
Skywatcher 200P with an astro modded Canon 700d, cls ccd filter, field flattener, guided by QHY 5Lm, PHD2
almcl
 
Posts: 68
Joined: Wed Jan 21, 2015 7:15 pm
Location: Shropshire. UK

Re: Correcting lens aberrations

Postby DorsetBlue » Tue Sep 13, 2016 7:29 am

Thanks, I will have a play and see what I get. :D
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