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Lenses and Optics

Sony FE 20mm f/1.8 G Optical Tests

Published February 10, 2021

I haven’t published much optical testing in the last year for many reasons; some obvious, some not. But published or not, we still test things, and occasionally something comes up that I think I need to write up. The Sony FE 20mm f/1.8 G is one of those things.

As wide-angle primes go, it’s reasonably priced at $800. My hope is it’s at least as good at f/1.8 as the more expensive f/1.4 primes. But the obvious comparison is the Sigma 20mm f/1.4 DG HSM Art. The Sony 24mm f/1.4 GM might be a logical comparison, but 20mm is significantly wider than 24mm, and the GM is almost twice the price of the 20mm f/1.8.

MTF Results

This is actually rather spectacular. The center resolution is phenomenal. (Remember, when comparing to an f/1.4 lens, being tested at f/1.8 gives an advantage, but even so, it’s phenomenal.) Resolution drops off slowly and steadily towards the edges. Most amazingly, there is almost no separation between the sagittal and tangential MTF, which means there is almost no astigmatism or lateral color.

Lensrentals.com, 2021

There is some variation, both in overall sharpness (the variation you see near the center of the graph) and in side-to-side variation (the increase in variation you see as you go away from the center).

Lensrentals.com, 2021

 

This isn’t awful, but it is a little worse than average for a wide-aperture prime. Here are a couple of ‘good variance’ wide primes; the Canon 24mm f/1.4L II and the Zeiss Milvus 21mm f/2.8 for comparison. Notice the Sony above is significantly sharper than the Canon, and math says higher resolution increases variance a bit.

Lensrentals.com, 2021

 

Field Curvature and Distortion

The field curvature here is remarkably flat for a wide-angle lens in both the sagittal and tangential planes. This is not an easy thing to accomplish. The flat field with little astigmatism makes it a superior lens for landscape, astro, and architectural work. It is a little bit softer in the outer 1/4 of the image, but that would, of course, improve as you stop down a bit.

Lensrentals.com, 2021

Measuring distortion in Sony lenses often leads to further discussion. Measuring just the lens on the bench (optics only, no camera involved) shows about 1.9% distortion in a mustache distribution.

Lensrentals.com, 2021. This sample is slightly tilted, but you can see the mustache pattern.

Tests using Imatest or other image computer target analysis (using a Sony camera) show a similar distortion pattern, but a much lower amount (0.7% or 0.8%), even with distortion correction turned off in raw conversion. I don’t like modifying raw files, so I mention it, but most people don’t care.

A Couple of Comparisons

I said earlier that this is a surprisingly good lens. Here’s a couple of comparisons to help visualize that.

Sony FE 20mm f/1.8 G vs Sigma 20mm f/1.4 Art

The Sigma has the advantage of a wider aperture and comes at an equivalent price.

The Sigma will sharpen up a bit at f/1.8 compared to the f/1.4 it’s being tested at. However, the Sony will still be significantly sharper in the center of the image and has far less astigmatism-like separation between the sagittal and tangential fields. In other words, unless you need f/1.4, the Sony is better.

Sony FE 20mm f/1.8 G vs Nikkor AF-S 20mm f1.8G ED

This isn’t really a fair comparison, the Nikkor is a full generation older than the Sony, but it is a good example of how far wide-angle lens design has progressed over the last 7-8 years. In this one area, newer is clearly better.

Lensrentals.com, 2021

Sony FE 20mm f/1.8 G vs Sony FE 24mm f/1.4 GM

This is probably not a really useful comparison; the 24mm is twice the price, a bit wider aperture, and not nearly as wide as the 20mm. Still, I think some people would be deciding between one and the other, or perhaps deciding that their zoom might cover 24mm, and the 2omm serve as a reasonably wide aperture prime.

Lensrentals.com, 2021

As discussed above, the 24mm will be sharper stopped down a bit. I didn’t have time to run a whole set of lenses stopped down, but did one copy of the 24mm f/1.4 at f/2.8 to demonstrate the change between wide open and stopped down. Even at f/2.8, though, the 24mm isn’t resolving much (if any) better than the 20mm f/1.8 at f/1.8. And it still has more sagittal-tangential separation.

lensrentals.com, 2021

 

So What Did I Learn Today?

I keep saying Sony lives out there on the cutting edge of technology, always going for the home run shot. Sometimes that results in a swing-and-a-miss,  but when it works, everyone leaves their seats. The FE 20mm f/1.8 is a home run. It’s really amazing. The resolution is awesome, the lack of astigmatism and lateral color is more awesome, and the flat field double-secret most awesome.

I can spew superlatives for a paragraph or two, but it’s really not necessary. Sony fanboys are going to do plenty of that because this is what they live for. If you want a wide-aperture prime for your FE system, get this one. If you don’t want a wide-aperture prime for your FE system, heck, get it anyway. You might be missing out. If you’re thinking about getting a 24mm f/1.4 GM, get this one instead and save a few hundred bucks. If you don’t shoot FE, well, prepare to listen to the Sony fanboys tell you why you should have.

 

Roger Cicala and Aaron Closz

Lensrentals.com

February, 2021

Author: Roger Cicala

I’m Roger and I am the founder of Lensrentals.com. 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.

Posted in Lenses and Optics
  • Roger Cicala

    Well, I tallied it up. Somewhere around 80 hours so afraid that’s a nope.

  • Trey Mortensen

    So I had the 24mm until an untimely drop… but now I have the 20mm and I vastly prefer it. I like the focal length better and the slightly smaller size. You CAN tell the difference in the aperture and bokeh, but it’s so minor as to be inconsequential.

    I find it interesting about the sample variation. I noticed that my copy has a tiny bit of coma in the upper righthand corner of my images when none of the test units that were sent out had it. Was it a deal breaker? No. Was it a little annoying when I was expecting something else? Yes. Otherwise, I totally agree with your conclusion. The 20mm is the better buy between the two lenses unless you really like the 24mm focal length (I have learned that I do not…).

    Now, if only Sony would have made their 35mm 1.8 like they did with this 20…

  • Maxi López

    E and Z lenses are outstanding! Now comparing Sony 20mm with Z20mm 1.8S MTF´s, the Z20mm is superior by a bit.
    And bringing the theme to the field… Canon is using same EF glass on RF and charging $o much.

  • Dave Burbank

    I think the chart is labeled right, but shows the wrong lens. Roger, can you show us the chart for the Sony FE 24mm f/1.4 GM?

  • Kers

    I really would like to see a comparsion of the new 12/12-24mm f/2.8 zooms; the Sony 12-24 f/2.8, the Sigma 14-24
    f/2.8 and the new Nikkor S 14-24 f/2.8- including Field Curvature and Distortion…
    but that is a lot of work… however, many would be interested.

  • bdbender4

    Still hoping for some Nikon Z lens tests, including the 20mm F/1.8. I thoroughly understand why you haven’t gone there so far, the technical reasons. But one can hope. Meanwhile I am truly happy for those who shoot Sony, what a great 20mm lens.

    Personally I am happy with the Nikon user interface on my Z6. Hitting tech home runs is great, and I honor Sony for it, but for me it’s not the only consideration. From using them, I suspect some of the Nikon Z lenses might also do pretty well MTF-wise. The 50mm and 85mm come to mind. Maybe even the 24-70 zooms (as zooms go), both the F/2.8 and the F/4. Dunno about the Z 20mm, haven’t used it.

  • Athanasius Kirchner

    Conspiracy theory time: Sony have some of the best UWA lenses now, although Nikon used to hold that title, and some former Nikon employees were hired by Sony… could this be just coincidence? ?

  • Jon

    Terrific test as always, thank you, Did you mislabel the right hand image under “Sony FE 20mm f/1.8 G vs Sony FE 24mm f/1.4 GM”?

  • Matti6950 .

    Take your time (or don’t do it if other things are necessary). Still as a very excited reader i cannot wait for reviews like Sigma 14-24mm, Sony 12-24mm GM, Sigma 85mm art (dg dn), you name it 😀

    Internet reviews not the same without you Roger 😀 But again no blame at all for not doing any tests. Any test is a damn nice bonus on the internet.

    Personal findings: Sigma 14-24 is incredible, wide open excellent in center, (good in corners but there is drop), stopped down primes barely do better (or they do worse actually), 14mm no lens is better (except new GM perhaps).

    Sigma 24-70mm: Sharper corners then GM for sure, just a feeling but less astigmatism. Definitely much less CA, better bokeh, middle focal lengths could be a bit worse then GM (but still excellent in real life use). 24/70mm ends are better especially 70mm. My sample of the GM is utter trash here even at f8, the resolution feels superior poor (at infinity).

    Sony 24mm GM F1.4 (bought before 20mm was a thing): Very happy about it, only thing misisng is that last ‘oomph’ of crazy sharpness that say a 85mm art might give or 35mm F1.2 art stopped down (and now sony 20mm G it seems). Still very happy about it. But the 20mm G is very high on my want list, i owned the nikon 20mm G, and it was the only lens with satisfying image quality below 24mm for me (i really disliked image quality of my nikon 14-24mm, it just didnt get sharp images often, something was off with it.

    Sony 100-400mm GM, can focus really close wich is super nice, but man that infinity sharpness is leading the pack. Better then 70-200mm G and GM for sure there. No regrets here!

    Sony 55mm F1.8, surprisingly sharp at F1.8 in corner, perhaps not as cutting good as newest lenses, but it’s damn close, with just loca/and lateral CA loosing it some resulution, stopped down, all this goes away and sharpness is near the best you can get. I don’t use much 50mm lenses, so i refrain from buying lenses like Sony Zeiss 50mm F1.4 (even though tempting), cause the low weight of 55mm makes it an easy ‘+1’ lens in bag, there to be used or sitting still, without hurting back much.

    Now i’m looking to buy an 85mm lens (Sigma is tempting), 35mm lens and f1.2, (and maybe Sigma 70-200mm FE mount when they release it.)

  • Dave Hachey

    Thanks for the article, it’s great to see some more MTF charts again. I have both the 20mm and 24mm Sony lenses, and can verify from field work what you say. The FE 20mm F1.8 G is outstanding, the best $800 I’ve spent in a long time. Now if Sony can get the FE 35mm F1.4 GM out to us, my lens lust will be sated.

  • Totally understand. Most of us spent 2020 doing what had to be done instead of what’s fun!

  • Roger Cicala

    It’s been a year of more doing what had to be done and less doing what’s fun to do, for me, just like everyone else. We should be getting back on track soon.

  • Roger Cicala

    I’m going to change over to ‘distrubution of resolution through space-time’.

  • Roger Cicala

    My most favoritist part of your thesis was the “that won’t be possible” response you got from a lot of people before you said hold my beer and watch this. 🙂

  • Brandon Dube

    Coma. The honest to goodness kind. When you see the word “coma” associated to line-like images of stars in the corner of a frame, 9/10 times it’s astigmatism. In this case, it’s “real” coma. A simple hint is that coma is linear with field, notice how the MTF drops almost linearly with angle?

    Obviously complex lenses contain more than one aberration, there is vignetting, etc. Simple hints. A trained eye can fish out most of the aberrations just from the MTF. A computer “can” do it automatically, too (this was my thesis).

  • seowgila

    So is there any reason at all to go for alternatives like the voigtlander 21mm 3.5 or the loxia 21?

    sunstars, colors etc?

  • Impulse_Vigil

    After looking at how they perform across a few reviews, it just strikes me as odd that the Z 20/1.8 is so much larger…

  • Impulse_Vigil

    Stumbling across a comment you made recently about the 20/1.8 G’s field curvature (or lack thereof) made me go back and look over a couple of the reviews that had convinced me to buy one last year…

    I didn’t really remember anyone talking about it, I don’t think any of the usual sites routinely test that at all, but I was surprised when I noticed Optical Limits had made a similar comment. Just kinda curious, I’d glossed over it amongst all the other praise.

  • Impulse_Vigil

    You joke, but I actually lusted after the M4/3 Voigtlander 10.5/0.95 for a good while, it’s one of the few lenses where the images it produced actually drew me in more than simple gear lust (tho looking back it might’ve been more about the forum members who were sharing images made with it)…

    I could never convince myself I’d be happy constantly dealing with manual focus at a 21mm EFL tho (even tho I was already using the Laowa 7.5/2), and it was kinda large and heavy for M4/3. When I started looking at E mount more seriously last year, the 20/1.8 G was hard to ignore. I’m loving it, plus it’s lighter and cheaper than the Voigtlander. 😛

  • Adam Palmer

    I’ve had the lens for a while and it’s pretty impressive. All of my other wide angles are just sitting lonely in the camera bag lately. I notice it has better contrast wide open than all my other 1.8 / 1.4 lenses too.

  • worldwolf

    Great review.

    BTW, the Sony FE 20mm f/1.8 G vs Sony FE 24mm f/1.4 GM chart is mislabelled as Sony 24/1.4GM vs Nikon 20/1.8G

  • Max Manzan

    Welcome back OLAF!
    Just wondering: since there is no astigmatism nor lateral color to speak of and the field is very flat, what is the reason for the very strong drop in image quality towards the frame edges and corners?

  • David Bateman

    Excellent I miss see these articles.
    No the real question is how does it stack up against the Laowa 10mm f2 in mft?
    Yes I had too.

  • Brandon Dube

    potentially confusing with flat fielding as done when calibrating a sensor.

  • Thomas Puckett

    I’ve had this lens for 6 months now and I use it for astro timelapses. When you nail that focus it is unreal.

  • 45Hunter

    I noticed that, too.

  • Mat

    I think all the non-Sony lenses compared here are limited by the fact these are SLR lenses, so the back of the lens needs to be way further from the image plane than the actual focal length of the lens (retrofocus design). Because of the shorter flange focal distance in mirrorless, I believe it is relatively easier to create a wide angle lens with very good image quality. So progress in lens design comes not only from 7-8 years difference, but also from different limitations that were put on the lens designers. By the way – I wonder how would the Sony lens compare with Nikkor Z 20mm f/1.8 as these are both mirrorless designs.

    PS. When comparing Sony 20 vs 24mm, MTF chart for Sony 20mm is mistakenly marked as Nikkor 20mm

  • Great to see MTF’s again! We’ve been waiting so very patiently!

  • It’s great to see an MTF test again: thanks Roger! The astigmatism performance is amazing on this lens, and that’s the headliner for me. Just amazing.

  • Franck Mée

    Stop talking about “field curvature”, talk about field flatness.

    (Well, you might tell me that a straight line is just a very specific form of curve. You’d be right after all. ? )

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