# Sigma 40mm Art review by Lenstip.



## Chaitanya (Dec 11, 2018)

Lenstip posted their review of Sigma 40mm art. 
https://www.lenstip.com/index.php?test=obiektywu&test_ob=548


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## chrysoberyl (Dec 11, 2018)

Thank you for posting. Another very impressive lens from Sigma. I wonder how concerned I should be about the spherical aberration.


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## Random Orbits (Dec 12, 2018)

chrysoberyl said:


> Thank you for posting. Another very impressive lens from Sigma. I wonder how concerned I should be about the spherical aberration.



I thought about that too... especially since EOS cameras tend to focus wide open. That and the focus accuracy isn't very good with non-center focus points:

When it comes to accuracy, like in the case of the A 105 mm f/1.4 DG HSM, a model we tested some time ago, we didn’t have any reservations concerning the centre autofocus point. With the side AF points the chances of blurry photos increased and the lens sometimes missfocused noticeably. Over all even 1/4–1/3 of all shots were slightly off. In the studio, on the other hand, while employing just the centre point, the number of misses never exceeded 3%.


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## MayaTlab (Dec 12, 2018)

chrysoberyl said:


> Thank you for posting. Another very impressive lens from Sigma. I wonder how concerned I should be about the spherical aberration.



Depends exactly on the quantity of focus shift as far as AF is concerned. I don't think that this is something the review covers and it's up to your own way of shooting as well. 

On the other hand a degree of spherical aberration can be seen as a very good thing for background blur transitions and bokeh quality, so reviews should perhaps stop mentioning it as a defect, but rather as a design choice to be made aware of.


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## chrysoberyl (Dec 12, 2018)

MayaTlab said:


> Depends exactly on the quantity of focus shift as far as AF is concerned. I don't think that this is something the review covers and it's up to your own way of shooting as well.
> 
> On the other hand a degree of spherical aberration can be seen as a very good thing for background blur transitions and bokeh quality, so reviews should perhaps stop mentioning it as a defect, but rather as a design choice to be made aware of.



An interesting perspective - but spherical aberration reduces sharpness at the same time. And yet this lens is very sharp. So perhaps the degree of spherical aberration is slight? This is confusing.


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## MayaTlab (Dec 12, 2018)

chrysoberyl said:


> An interesting perspective - but spherical aberration reduces sharpness at the same time. And yet this lens is very sharp. So perhaps the degree of spherical aberration is slight? This is confusing.



I would guess that lens engineers are increasingly able to finely tune aberrations to find a good compromise between resolution and rendering of OOF areas. The Canon 50mm RF, wide open, also bias the blur wide open for increased rear smoothness and yet is very sharp as well. It's quite apparent in that shot : https://4.img-dpreview.com/files/p/sample_galleries/4037492029/9020232199.jpg
A few years ago Nikon communicated on their new approach to measure and design lenses (search for Optia), which apparently increased their ability to understand how aberrations influence OOF areas and I would be surprised if Canon, Sigma, and others couldn't do the same. 
I also don't think that Lenstip knows how to test for spherical aberration anyway. They said that the Nikon 105mm f1.4 ED's spherical aberration was "vestigial" and I'm not sure that this is the case .


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