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Sigma 20mm f/1.4 DG HSM A1 MTF Curves

Published November 28, 2015

OK, here we go again, with what has become a regular routine. Sigma announced another new lens doing what nobody has been able to do before. My expert friends, technical people I ask questions of, all say, “I don’t know this time. I just don’t see how they can pull this one off. Not at that price point. When are you going to test it?”

And then I test it, and tell everyone Sigma has done it again. (That groan you just heard is the blog editor who HATES when I don’t build up suspense and make you read to the end.) And yes, I realize I’m starting to be called a Sigma Fanboy. But that’s kind of like shooting the messenger, isn’t it? I’m just putting the lenses on the machine and writing up the results.

Let’s face it, Sigma is just hitting one home run after another. I don’t really have any use for a 20mm f/1.4 lens myself and I’ll never buy one. But I’m a geek and there’s nothing cooler to me than a company who likes doing stuff nobody has ever done before, and then does it better than anyone believes possible. So, OK, maybe I am becoming a Fanboy.

Anyway, let me show you what Sigma has accomplished as far as making a f/1.4 lens wider than any other SLR manufacturer has been able to do. Before you minimize the difference between a 24mm f/1.4 and a 20mm f/1.4, let’s just mention that’s a really big difference. So my expectations going in were that the Sigma 20mm f/1.4 DG HSM A1, even if it was great, wouldn’t be quite as good as either the Canon or Nikon 24mm f/1.4 lenses.

MTF Curves

As always – we are showing the average of 10 copies of each lens, each copy shot at 4 rotations to give a complete cross-section of the field of view of the lens.

Roger Cicala, Olaf Optical Testing, 2015


Roger Cicala, Olaf Optical Testing, 2015


The bottom line here is pretty obvious. Despite being a wider field of view, the Sigma 20mm f/1.4 clearly has a higher resolution than either the Canon or Nikon 24mm f/1.4 lenses do in the center half of the image, and are at least the equal of the others in the outer half. That’s just flat amazing. Even more amazing to those of us who have in the past shot the old Sigma 20mm f/1.8 lens, which could be charitably described as ‘artistic’, but never described as sharp.

Of course we checked the variation between copies, too. Again, given the wider field of view I wasn’t going to be surprised at a lot of variation between copies. We always expect wider lenses to vary more than standard range.


Roger Cicala, Olaf Optical Testing, 2015


Roger Cicala, Olaf Optical Testing, 2015


The variance plots for the Sigma look decent, certainly as good as the Nikon although perhaps not quite as consistent as the Canon. Still, I think it’s an excellent performance for a lens that’s significantly wider than the two we are comparing it to. Not to mention significantly less expensive.


With a wide-angle, wide-aperture prime lens, MTF is probably not the main consideration in whether you buy the lens or not. Theses lenses are used for different things by different photographers and bokeh, handling, vignetting, and dozens of other things I don’t test for will make a bigger difference in whether you like the lens, rather than simply how sharp it is.

Everyone’s first comment seems to be, “Well, I don’t need a 20mm f/1.4 lens”. I said that myself. But then I realized, well, I’ve never had the opportunity to use a sharp 20mm f/1.4 lens before, because there’s never been one . Will I like it? I have no idea. But I think I’ll at least check it out, it might be fun. Especially at this price point.

But the geek in me, at least, is totally impressed. Wider, faster, sharper, cheaper. What’s not to be impressed by?


Roger Cicala

November, 2015


Author: Roger Cicala

I’m Roger and I am the founder of Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.

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  • kamran zafar

    does these mtf result are at all lens aperture ie. ar f-1.4-1.8-2-2.8… till f16 or these mtf at a specific one aperture i.e 1.4 only.

  • Roger Cicala

    Kamran, please read the posts before critiquing. We don’t use a camera, we use an optical bench. You can’t generate MTF curves with a camera, only do Imatest or DxO type testing.


  • kamran, please read the posts. We don’t use a camera. These are tested on an optical bench, hence the titles “Just the lenses” we used for months when we started these.

  • kamran zafar

    you never mention which camera you have mounted these lens when making a review,it would be helpful if you mention the camera type,because comparing mtf from two different lens mounted on two different dslr is not really a comparison.

  • Joachim (CH)

    I also was one of the “who needs a 20/1.4, when one already got a 24/1.4?”-persons. And although looking nice, the variance number was not too impressive. But then I saw a couple of pictures by Wataru Nakamura ( – please feel free to delete the link, Roger, if it’s inappropriate to post it). They got me. Mostly done wide open and very natural looking without noticeable distorsion. Three days later I had one and am really pleased! The question remains if I need 24 mm AND 20 mm, but if I’d like to go “light”, the 20 mm is not the first choice. It’s definitely more options and high value.

  • Mike Cranstoun

    I like it,I just wish the hood was removable.Im planning on renting it.

  • Ilya Zakharevich

    Tony, could you explain how one can understand what happens when “stopping the lens down” by just looking at the MTF curves?

    My understanding goes like this: the performance at f/1.4 and at (say) f/5.6 are completely independent (except that optimizing for one would?—?most probably?—?ruin the other one). There is no possibility to “predict” anything. Do you have a different idea?

  • AJ

    Be interesting to compare this lens with the Zeiss 21mm as the closest in F/L on your database?

  • Roger Cicala

    Omesh, I’ll try to get to the Tamrons next week.

  • Hi Roger, thanks. This 20/1.4 looks amazing. My trusty Canon 24L-II looks like it could by under serious threat.

    p.s. Any tests on the new Tamron 1.8 VC lenses? It appears you’ve got them in stock.

  • Tony A.

    For those who are asking about how useful this lens will be for wide star field astrophotography at wide open apertures, a lot of what you need to know is right there in the droop of the mtf curves towards the frame edges. You don’t need to confine your concern to the C-word. Those curves are telling you that you can benefit from stopping the lens down no matter what the dominant aberrations are named.

    Most of my rentals have been lenses that I’ve been interested in at least in part for use on star fields. There have been some pretty high end lenses in that list, several of them with nosebleed prices in the form of top primes from Nikon and Zeiss. The widest aperture I’ve encountered so far that gives convincingly round star images in the corners under close examination is f/3.5. That one happens to be a telephoto.

    If you aren’t making giant prints there’s a useful tradeoff zone where as you work your way towards wide open apertures you are also moving towards smaller presentation sizes.

  • Ilya Zakharevich


    > in that range of best focus the LED image distorted
    > between vaguely radial to vaguely tangential shapes.

    This means that the most visible component of aberration is ASTIGMATISM (possibly combined with COMA and CHROMATIC CHANGE IN MAGNIFICATION). The other components on top of this contribute as your “vaguely”.

    (With pure astigmatism, the sizes of these “tangential” and “radial” shapes would coincide. The added coma would make the radial part longer, AND would widen the tangential part. Etc…)

  • Peter

    Just like NancyP I wonder about coma. I make aurora timelapse series, which requires short shutter, large aperture and high ISO. I use a Canon 24mm 1.4, but any stars or light sources away from the middle produces terrible coma. I don’t care about vignette or aberration because they easily get adjusted in raw processing, but that doesn’t apply to coma. And I rarely see it being tested in reviews.

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