# Post processing, coma removal



## chrysoberyl (Aug 20, 2014)

Is it possible to correct coma in post processing? Specifically the coma that results from the Canon 24mm f/1.4 and the Sigma 85mm f/1.4.


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## NancyP (Aug 20, 2014)

It would be wonderful, but, unfortunately, NO post-processing corrections are available in major programs. Expert astrophotographers, any obscure programs out there that correct coma? My suggestion is to live with it, stop down to f/2.8 or f/4, or to buy inexpensive manual focus Samyang 24 f/1.4 specifically for astro, night photos.


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## mackguyver (Aug 20, 2014)

DxO Optics Pro does correct for coma (see here), but mostly in terms of color smearing, not point light sources like stars.

Your best bet is to follow Nancy's advice and get a Samyang lens - they are cheap and offer much better coma performance than Canon's fast primes. Lenstip.com tests for coma and according to their tests and the advice of others on this forum, the only Canon lenses that have good coma correction are:

16-35 f/4 IS
24-70 f/2.8 II 
70-200 f/2.8 IS II 
TS-E 17 f/4
TS-E 24 f/3.5

I own all of these and can vouch for their performance, but they are all somewhat slow compared to the Samyang lenses. I also happen to live in Florida where astrophotography is a 1-2 month possibility, so I'm no expert. Do a search for "coma" on the forum and you should get lots of good results from other members.


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## chrysoberyl (Aug 20, 2014)

NancyP – thanks for the advice and the recommendation. I have the Tokina 16-28 and will try that next. How do you feel about the Samyang 14mm?

Mackguyver – thanks to you, also. It had not occurred to me to use my 70-200 for night skies. The next time I’m where I can, I will do that. I live just outside of Atlanta, so I too have limited access to quality night sky.

BTW, I did search for ‘coma’ in the forum search feature and got zero results. I think the search feature is a bit iffy.


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## mackguyver (Aug 20, 2014)

chrysoberyl said:


> BTW, I did search for ‘coma’ in the forum search feature and got zero results. I think the search feature is a bit iffy.


Make sure you click on the Search button at the top of the forum between Help & Profile, not the Search... box on the right. I got 8 pages of results.


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## chrysoberyl (Aug 20, 2014)

mackguyver said:


> chrysoberyl said:
> 
> 
> > BTW, I did search for ‘coma’ in the forum search feature and got zero results. I think the search feature is a bit iffy.
> ...



Aha! Thanks again.


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## Frodo (Aug 20, 2014)

Yes, I'd love to be able to correct coma. My EF35/2 IS is a wonderful lens, but the poor coma renders it useless for landscape astrophotography.


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## mackguyver (Aug 20, 2014)

One other thought - I wonder if the Digital Lens Optimizer for DPP would correct coma. I have played around with it some, but never with night scenes.

It looks like it might be worth a try from this post on CPN: 
DPP 3.11 software explained

"Working with RAW images, Digital Lens Optimizer is able to correct seven types of lens aberrations and diffraction loss. The seven kinds of aberration that are corrected are:

Spherical aberration – this is image blur occurring in the centre of the image.
Curvature of field – this is blurring at the periphery of the image caused as a result of the lens’ focussing surface being curved.
Astigmatism – this is the blurring in the radial and circular directions at the image periphery.
* Comatic aberration – this appears at the periphery of the image in a radial direction as image streaking or colour blurring.*
Sagittal halo – this appears in the periphery of the image as a circular blur.
Chromatic aberration of magnification – this is the chromatic blurring at the periphery of the image.
Axial chromatic aberration – this is the mainly violet coloured blur that occurs in the centre of an image that has pinpoint light sources."


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## tron (Aug 21, 2014)

It wouldn't!

The choices are: Peripheral Illumination, Chromatic Aberation (R & B), Color blur, Distortion.


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## mackguyver (Aug 21, 2014)

tron said:


> It wouldn't!
> 
> The choices are: Peripheral Illumination, Chromatic Aberation (R & B), Color blur, Distortion.


Thanks for the info. It looks like this is something that you need to get right during the capture unless there's some tool out there that can do this PP.


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## tron (Aug 21, 2014)

mackguyver said:


> tron said:
> 
> 
> > It wouldn't!
> ...


Exactly! The best solution is another lens as was suggested before.

By the way the Canon 24mm 1.4 has terrible coma.


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## tron (Aug 25, 2014)

I am thinking of Samyang 24mm 1.4 but it is not as wide as I would like plus, it is reported having decentering issues...

In addition, compared to my Canon 14mm 2.8L II the advantage is not 2 stops but 1 1/3.

The reason. With 14mm I shoot at 25sec in order to avoid star trails.
With 24mm I would shoot at 15 sec hence the 2/3rd stops less. So subtract this from the 2 stop difference and you have a 1 1/3 stop advantage.

Even so it is not bad but you still have to be satisfied by 24mm view of field. I personally prefer something wider...


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## raptor3x (Aug 25, 2014)

tron said:


> It wouldn't!
> 
> The choices are: Peripheral Illumination, Chromatic Aberation (R & B), Color blur, Distortion.



The other corrections are all controlled by the DLO slider, you can't adjust them individually like the ones you listed.


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## tron (Aug 25, 2014)

raptor3x said:


> tron said:
> 
> 
> > It wouldn't!
> ...


Do you have an example where coma is being corrected at post via DLO?


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## tron (Aug 25, 2014)

Coma test of Samyang 24mm 1.4

http://www.lenstip.com/330.7-Lens_review-Samyang_24_mm_f_1.4_ED_AS_UMC_Coma__astigmatism_and_bokeh.html

It is not coma free but it has much less coma than the Canon.

Reading though:

http://www.lenstip.com/330.11-Lens_review-Samyang_24_mm_f_1.4_ED_AS_UMC_Summary.html

I have some reservations(Quoting from the aboe lenstip link):

"Coma looks practically the same, no matter whether we use f/1.4 or f/2.0."
"Defocused diode images, positioned in the corner of full frame are practically the same by f/1.4 and f/2.0"

To sum up there is some doubt whether this is truly a 1.4 lens. Some findings are explained, some not.


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