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Sigma 105mm f1.4 Startest - Should I keep it?

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#1 skanker

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Posted 08 August 2020 - 02:11 AM

Hello from Austria!

I bought a Sigma 105mm f1.4 A and would like to hear your opinion on the imaging performance. I could still give the lens back.

I did tests with a Canon 6Da and a Canon 77Da. The focus was always on a star in the center of the picture (with Bahtinov  Mask).

6Da - JPEG - f1.4 - ISO 200 - 25 seconds

https://www.bilder-u...726604.jpg.html

77Da - JPEG - f1.4 - ISO 200 - 25 seconds

https://www.bilder-u...726737.jpg.html

You can find uncompressed TIFs here:

https://drive.google...IS2?usp=sharing

The vignette has been removed from the test images in Camera Raw. Otherwise they are not processed.

With the 77Da it is noticeable that the stars in the center of the image are not as sharp as those at the edges. What could be causing this?

Should I keep the lens or would you return it?

CS



#2 Jerry Lodriguss

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Posted 08 August 2020 - 02:31 AM

Hello to  Austria!

 

First, you are shooting with modified cameras, so you're going to see more red halos.

 

The stars may seem not as sharp in the 77Da because it has 3.72um pixels, and the 6Da has 6.5um pixels.

 

Were these shot with filters (I see them in the file names)?   

 

If so, filters will degrade the optical performance.

 

These are not full-frame cameras, so you are wasting a lot of the aperture, but the performance on the stars in the corner of the full frame are not critical because they are not in the field of the crop sensor camera.

 

I'm sure you realize how critical focus is at f/1.4. I don't have any problem focusing my Sigma 105mm f/1.4 just with Live View, I don't use any masks,ever.

 

Considering you had a filter on, and used a modified camera, I think these look pretty good.

 

Jerry


Edited by Jerry Lodriguss, 08 August 2020 - 02:32 AM.

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#3 skanker

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Posted 08 August 2020 - 02:41 AM

Hello Jerry!

 

The pics in the links were shot without filters! In the Drive folder you will find one 6D shot were I used a Optolong L-Pro clip in filter.

 

Check out this measurement of the 77Da: https://www.astrobin.com/p9o6h3/0/

 

I focused on a star in the center of the image... Strange isn't it?

 

CS



#4 Aleksandr Naumov

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Posted 08 August 2020 - 02:47 AM

On 6Da shot, there is bright star at bottom with significant diffraction spikes.

 

Since this shot made with fully opened aperture,

what could cause these spikes?

 

Also, stars at left corners are quite different from stars at right corners,

think I would be scared and probably willing to return this lens.



#5 skanker

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Posted 08 August 2020 - 04:14 AM

On 6Da shot, there is bright star at bottom with significant diffraction spikes.

 

Since this shot made with fully opened aperture,

what could cause these spikes?

 

Also, stars at left corners are quite different from stars at right corners,

think I would be scared and probably willing to return this lens.

Maybe the spike is caused by the edge of the mirror box. The sensor is located quite deep in the housing of the 6d!

 

But hey its f1.4 on a full frame smile.gif


Edited by skanker, 08 August 2020 - 04:33 AM.


#6 ChristopherBeere

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Posted 08 August 2020 - 08:06 AM

Looks like you have minor tilt.

 

The stars in the top corners of the frame exhibit very minor batwings - which is normal for the Sigma Art 105mm at f/1.4

 

The stars in the bottom corners do not exhibit batwings but there is coma elongation, again not unusual at f/1.4

 

I would be tempted to try another copy if thats a possibility because my Art 105mm is a lot more consistent across the frame than that.

 

Ive uploaded a RAW of a very dense star field in Cygnus shot on my full frame modded 6D MKII at f/1.4 on the Sigma Art 105mm so you can see what im talking about in terms of consistency.

 

https://gofile.io/d/nwkKXu


Edited by ChristopherBeere, 08 August 2020 - 08:07 AM.

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#7 garret

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Posted 08 August 2020 - 11:33 AM

Looks like you have minor tilt.

 

The stars in the top corners of the frame exhibit very minor batwings - which is normal for the Sigma Art 105mm at f/1.4

 

The stars in the bottom corners do not exhibit batwings but there is coma elongation, again not unusual at f/1.4

 

I would be tempted to try another copy if thats a possibility because my Art 105mm is a lot more consistent across the frame than that.

 

Ive uploaded a RAW of a very dense star field in Cygnus shot on my full frame modded 6D MKII at f/1.4 on the Sigma Art 105mm so you can see what im talking about in terms of consistency.

 

https://gofile.io/d/nwkKXu

Yes the 6d image doesn't look good, but I guess it is tilt in the camera sensor?


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#8 garret

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Posted 08 August 2020 - 11:38 AM

 

Maybe the spike is caused by the edge of the mirror box. The sensor is located quite deep in the housing of the 6d!

Yes!, I have the same issues with bright stars at the edge with my Canon 5 dmk2.



#9 robbieg147

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Posted 08 August 2020 - 12:22 PM

I think you are asking a lot of any camera lens using it wide open for astro, stopping down to say F2 may be a bit more would improve things quite a bit? and also help with focus.

 

As said above I think your images look quite good.



#10 skanker

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Posted 08 August 2020 - 02:14 PM

Looks like you have minor tilt.

 

The stars in the top corners of the frame exhibit very minor batwings - which is normal for the Sigma Art 105mm at f/1.4

 

The stars in the bottom corners do not exhibit batwings but there is coma elongation, again not unusual at f/1.4

 

I would be tempted to try another copy if thats a possibility because my Art 105mm is a lot more consistent across the frame than that.

 

Ive uploaded a RAW of a very dense star field in Cygnus shot on my full frame modded 6D MKII at f/1.4 on the Sigma Art 105mm so you can see what im talking about in terms of consistency.

 

https://gofile.io/d/nwkKXu

Thx for providing the RAW!

 

Your pic looks really good smile.gif

 

I tested the lens with a Canon 5D Mark IV @f1.4 and it shows the same batwings...

 

https://www.bilder-u...885476.jpg.html

 

I think a sensor tilt is therefore not possible!?

 

 

CS


Edited by skanker, 08 August 2020 - 02:15 PM.


#11 ChristopherBeere

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Posted 08 August 2020 - 02:59 PM

Thx for providing the RAW!

 

Your pic looks really good smile.gif

 

I tested the lens with a Canon 5D Mark IV @f1.4 and it shows the same batwings...

 

https://www.bilder-u...885476.jpg.html

 

I think a sensor tilt is therefore not possible!?

 

 

CS

 

No worries waytogo.gif

 

If its not tilt then the only other thing i can think of is that the lens is decentered so definitely get another copy.


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#12 skanker

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Posted 09 August 2020 - 03:40 AM

I will try another copy of the lens! The image quality of Christopers Sigma is much better.
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#13 Aleksandr Naumov

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Posted 09 August 2020 - 03:56 AM

Looks like you have minor tilt.

 

Ive uploaded a RAW of a very dense star field in Cygnus shot on my full frame modded 6D MKII at f/1.4 on the Sigma Art 105mm so you can see what im talking about in terms of consistency.

 

https://gofile.io/d/nwkKXu

Thank you!

 

That's what I would expect from Sigma Art at 1.4



#14 calypsob

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Posted 09 August 2020 - 11:21 AM

It looks pretty good to me. You could do some star shrink in post if the full frame gives you issues. honestly it may not even be an issue once you stack some subs.  



#15 skanker

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Posted 15 August 2020 - 04:33 PM

Hello!

 

I tested a new copy of the lens! Here are the results:

 

Canon 6D - no filter - f1.4

https://www.bilder-u...526740.jpg.html

 

Canon 6D - no filter - f1.4

https://www.bilder-u...526894.jpg.html

 

Canon 77D - no filter - f1.4

https://www.bilder-u...527162.jpg.html

 

 

The weather conditions were not ideal! It was very humid and there were light cirrus clouds.

 

What do you think about the performance of the new one?

 

CS


Edited by skanker, 16 August 2020 - 02:54 AM.


#16 ChristopherBeere

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Posted 16 August 2020 - 10:29 AM

Thats a much better copy, a lot more consistent in the corners.


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#17 skanker

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Posted 16 August 2020 - 01:10 PM

Thank you for your evaluation Christopher :)

 

Are there any other opinions about the test images of the new lens?

 

CS




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