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Lenses and Optics

Just the Lenses: Sigma 24 f/1.4 Art Comparison

Published April 2, 2015

Most of you know I’ve been very impressed with Sigma’s new Art lenses. Their 35mm f/1.4 Art I still think is the sharpest 35mm prime lens made. The 50mm f/1.4 Art is also superb.

When I heard about the Sigma 24mm f/1.4 Art lens, I had some mixed emotions. I was excited that we might get a 24mm lens of similar quality to their 35mm. But the logical side of me thought that perhaps Sigma had bitten off a bit more than they could chew this time. Designing a wide-aperture 24mm lens is much more difficult than designing a fast 35mm lens. Even the best 24mm f/1.4 lenses (I consider the Canon 24mm f/1.4 L to be the best current offering, although that’s arguable) still have distortion, aberrations, and some edge softness.

But when our first five copies of the Sigma 24mm f/1.4 arrived, I swiped them from intake and took them over to the testing lab for a quick look and MTF testing on our optical bench. We already had results from the Canon 24mm f/1.4 L, the Nikon 24mm f/1.4 ED AF-S, and the Rokinon 24mm f/1.4 lenses in our database to compare them to.

MTF Tests

As usual, MTF testing was done for five copies of each lens. Each copy was tested at four rotations (0, 45, 90, and 135 degrees) to give an average MTF across the entire surface of the lens, and the results for each lens then averaged. Prior to MTF testing, all lenses were double-checked on OLAF, our 5-micron pinhole collimated testing machine, to assure they were well-centered. Since the Sigma was the focus of this post, I’ll show its MTF curves compared to each of the other 24mm f/1.4 lenses.

Legend for all the MTF graphs

 

 

For those of you who don’t speak MTF, I’ll summarize a bit. In the center 1/2 of the lens (from 0 to 10mm) the Sigma clearly is more contrasty and has better resolution than even the Canon lens, especially at higher (40 lp/mm and 50 lp/mm) frequencies. In the outer part of the image (from 15mm to 20mm) though, the Canon and Sigma are about the same.  The Sigma is better than the Nikon all the way out to 15mm, but again, in the outer areas there is either no difference or the Nikon is slightly better.

The Rokinon is a rather different lens. It doesn’t resolve as well as either the Nikon or the Canon, and not nearly as well as the Sigma in the center of the image. The Rokinon’s advantage is that its curves remain flat almost to the very edge of the image circle, and again in this outer 1/4 of the image it is as good as the Sigma, or perhaps a bit better.

What the MTF curves suggest, then, is that Sigma has made the best resolving 24mm lens in the center of the image, but at the outer edges they’ve run up against the same aberrations and problems that designers of 24mm lenses have always faced, and haven’t managed to overcome those.

Field Curvature

We haven’t always included field curvature diagrams in this little reports, but 24mm wide-aperture lenses tend to have a lot of curvature so it seemed a good idea.

You’ll notice, of course, that the difference in Sagittal and Tangential field curvatures parallels the increased astigmatism areas you see on the MTF graphs above. But notice also how the fields curve very severely in all of these lenses out in the edge area of the image, from 15mm to 20mm. This is part of the problem we always see with 24mm wide-aperture lenses and it seems that current lens technology cannot quite overcome this.

It might help to give you an image from Olaf, our 5-micron pinhole machine we use for testing centering. With the lens set at infinity focus, we manually focus the lens a few microns at a time.

If we focus on the center point, the corners are well out of focus, like this:

Sigma 24mm focused on center point (bottom image). Upper images show the two sides at 20mm.

 

We can focus on the edges and make them nice and sharp, but doing so defocuses the center quite badly.

Sigma 24mm f/1.4, focused on edge points (top boxes) at f/1.4

 

Even stopped down to f/5.6 the focus plane at center and edge is quite different.

Sigma focused on center point at f/5.6

 

Sigma focused on edge points at f/5.6

 

Let me be clear here: the Nikon and Canon lenses are not any better as far as field curvature. I just saw no reason to post all those images up to show you the same thing over and over. The Rokinon is not as extreme, but then part of that is because it’s never as sharp at any point as the others are. I should also mention sample variation with the latter lens is much greater – you’ll rarely see both sides in the same focus plane with that lens.

Summary

The new Sigma 24mm f/1.4 Art lens does, indeed, out resolve the offerings from the major manufacturers, at least in the center of the image. At the edges, though, the advantage disappears. More importantly with any 24mm f/1.4 lens, try as you will, unless you really stop the lens way down you aren’t going to get a flat field of focus. And if you are going to stop the lens way down, why invest all the extra money for a wider aperture lens.

That doesn’t make these bad lenses. There are clearly some types of photography that this focal length is invaluable for, and in that case you just learn to work around the shortcomings. In many cases, though, the old rule that the best 24mm f/1.4 is a 35mm f/1.4 and a few steps backwards is often true.

 

Roger Cicala and Aaron Closz

Lensrentals.com

April, 2015

 

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
  • Eric

    I have the same question as Larry. If you are willing to use a tripod and are interested in landscape and architecture which wide angle lens would be the best at f4-f8? I still use the old 17-35mm Nikkor and can’t understand the bashing on that lens. If you are not interested in the corners the lens produces wonderful pictures even on my D810. The pictures are not clinical clean but have this slight imperfectness many people like at pictures taken with a film camera.

    Btw. I don’t understand the approach to test lenses always at highest aperture. It is like to test acceleration of a car always till 30% of speed max and not to a fixed and comparable value. A f1.4 lens give me additional opportunities compared to a f2.8 lens, but I want to know which one deliver better results at f4.

  • Larry Watson

    How does the Zeiss 25mm f2 stack up against these 24mm lenses? Does the Zeiss 25mm f2 have sharp corners? I want a wide lens for landscapes that would be sharp in the center and corners at the same time. It would be fine if it could achieve that at f8 as far as I’m concerned. I don’t need f1.4 or even f2. It could be a 2.8 lens that was sharp in the center and the corners at F8. Does such a lens exist in the 24-25mm range?

  • Hehey! Thank you for awesome review! On my part I did real life AF speed test here:

    https://youtu.be/N7rmcRo0r2E

  • Carl

    Roger, bravo again, I loved reading this! (Also loved your April Fool’s piece, lol! I would be happy with a 60-160mm f/1.6…)

    So, for Milky Way shots on a D810, what is going to be better than the Zeiss 21mm f/2.8 Distagon? The Sigma 24 Art, or the Nikon 20mm f/1.8, or something else…or nothing? I realize many use the 14mm or similar focal length, but I found I really like even using my 35mm Art (closed to from f/2 to 2.8). But it is Canon mount, and I find myself wanting to get into Nikon next year.

    As you say, to make a wide angle lens with a flat field, is either very difficult, or impossible, especially with a fast aperture lens…

    The Distagon appears to vignette significantly at borders and corners at f/2.8…and the Nikon 20mm f/1.8 looks like a lot of astigmatism setting in by mid frame…

  • I’d be curious to know if the corner performance/coma issue extends to the new Nikon 20mm 1.8f – it would fill the same purpose as a 24mm for dance floor photography but might be better for astro.

  • Cyron

    Hello, could you say something to the Bokeh of the new sigma? Thank you.

  • ewg

    Where is the infinity side in the field curvature diagrams – up or down?

  • Roger Cicala

    CLiff, not any noticeable difference that I could tell. A degree or less of tilt is pretty common and I haven’t noticed any real difference other than with the Rokinon 24s.

  • Roger thanks for the information…
    I have the Sigma 50 Art and it is about the best lens i own. I think the problem with this 24mm Sigma lens is that they wanted to make it at the same pricepoint as the other ART offerings. I suspect that it would have to cost 2x that price to make it any better than the canikons. I would have liked it though because all my 24mm lenses have their problems. together they do the Job. 24PCE- best for indoor shooting- to much field curvature but indoor a +- the 14-24mm on 24mm – best on landscapes- sharpest in the corners- the 24mm 1.4: beautiful bokeh at 1.4- very nice for portraits- very good for macro- and of course dark situations.
    I do not think we will ever see an Otus 1.4 24mm lens- it would cost too much to make it good enough.

  • user

    The right side of all the images is cut off on mobile making the article unreadable

  • Cliff

    I noticed that both the Nikon and Canon field curvature diagrams showed a little tilt to them and the Sigma was almost symmetrical. Was there much variation in the centration or/or tilt of the five samples from Sigma that you tested? Or should I say less variation than you normally find in Nikon and Canon?

  • That sound you hear is all the astro-landscape photographers exhaling in a huff. I guess we wait for a Rokinon 24mm f/1.4 mk2, then? Maybe it will have better build quality?

    I mean, I don’t blame Sigma for allowing a little coma etc. in favor of eye-popping center sharpness. It was the right move, for the bulk of the potential buyers.

    I suppose I’ll buy the Nikon 20mm f/1.8, get a few mm wider, and put up with seagull wings in the corners of my astro images. 😉

  • Randy

    Thanks, Roger. The fact that a lens is really sharp in the center is nice to know but most lenses are.

    When I check out a wide angle, I go straight to the corners. If they’re not outstanding and equally sharp all the way around I figure the lens is nothing special.

  • Roger Cicala

    Dvir, unfortunately Sony E lenses use an electromagnetic focus system, not mechanical, so we can’t test most on the bench. The alphas we don’t have enough copies of most to make testing practical.

  • Roger Cicala

    David, I haven’t been able to find a Rokinon 24mm lens that doesn’t have tilt, and I didn’t really want to get into that. The copy-to-copy variation in those is large and they can’t be optically adjusted.

  • David

    Roger, could you you provide the field curvature diagram for the Rokinon 24mm as well? I know this is primarily about the Sigma… but the omission seems particularly glaring here, if it is the most flat-fielded of these lenses.

  • Dvir Barkay

    Would be nice to also include sony alpha comparisons in tests like these to see the comparison across all three formats. Would be interesting to see the Sony Ziess 24/2 in such a comparison.

  • Mal

    Thanks for all your hard work, Roger! You’re providing us with a lot of great information. A question on this post: what is the field curvature of the 24mm TS-E lens just shot straight. I know we don’t usually use it as a plain 24mm lens, but I am curious how the TS constraints affect the curvature and other measurements. I’ve been told that they actually accentuate the field curvature to make focus on tilt easier.

  • Coyote

    Roger,

    Since we are on the subject of 24mm lenses, can you post the field curvature of the Canon TS-E 24mm f/3.5 II? It’s not f/1.4 like these, but when I need 24mm, that’s the lens I reach for.

  • Leif M

    The link to the 50mm f/1.4 Art lens actually leads to the 35mm lens?

  • Chris

    Hey guys, if you’d like to see a full video review of the 24mm from Sigma, I did a review here ? https://www.youtube.com/watch?v=OHMMeM53cmk

  • Roger Cicala

    Martin, the simplest thought is if you’re shooting stopped down, there’s no advantage for most people in buying the f/1.4 lens. The f/2.8 lenses generally do better stopped down than the f/1.4 lenses do – very true in the case of the Canon, for example.

  • Martin

    Hi Roger and Aaron

    Great work as always! Is it possible to get your thoughts and results at other apertures? Most will be using these wides stopped down.

    Thanks

  • Craig

    Any thoughts on the Sigma Art 24 vs. the Tamron 15-30 at its 23mm “sweet spot”? Not expecting a zoom to match a prime, but the Tamron did edge out the Nikon 14-24 at that focal length.

  • I have compared Sigma 24mm f1.4 with Canon 24m f1.4 L II.
    http://i-gear.tistory.com/entry/Sima-24mm-f14-Review
    I agree that art 24mm f1.4 is not good as art 35mm f1.4.
    The reason may be the difficulty in design more wide angle lens.

  • Brian Caldwell

    It seems that there may be a reason for Zeiss to expand their OTUS line into shorter focal lengths after all . . .

  • Roger Cicala

    Max, it is, we just don’t do it. Our primary purpose is optical standardization and adjustment and that’s all done at widest aperture.

  • HobbyPhotoG

    Interesting how most of the major manufacturers don’t offer top-quality “slow” prime lenses except for ultra-tele and some macros. The slower primes are usually optically inferior, “affordable” models.

    Clearly this new design is looking like another jackpot for sigma, but a no-compromise f/2 design could have more expensive glass, less weight and deliver better images (except from f/1.4 through f/1.8, of course).

  • There would probably not be a huge demand, but as a backpacker I wouldn’t mind well-built and sharp prime lenses that have a smaller aperture and a smaller weight. I’d rather carry a handful of small prime lenses than a handful of large prime lenses or a couple large zoom lenses that aren’t as sharp in the corners and are even heavier!

  • Max

    Hi guys,
    extremely interesting and useful findings, thanks a lot for your effort!
    Just a small question: time problems aside, is your MTF-bank able to measure MTFs for stopped down apertures?

    Best,
    Max

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