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Context

I realize that the above four focal lengths lend to having a different perspective that make them all unique. It might be possible to use one as the other but that isn't always true with the extremes. I'm debating on prime lens and I'm curious how each of those (with the focal length) are built and (ignoring the perspective given) how good they are optically.

Question

In terms of the four focal lengths (24, 35, 50 and 85) is there one that tends to leads to the sharpest lens built? Is that lens has the least distortion?

I don't know if sharpness is also judged by your subject but if that is the case I'd use it mainly for street photography. I realize that 85mm is very odd for that but doesn't mean you can't compose and see the world in a different way.

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    Sharpness has nothing to do with the focal length. – Dragos Dec 16 '15 at 19:08
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    @Dragos I don't think that's strictly true. Focal length does factor into the design of the lens — what designs work, what compromises are necessary, what options are available. – mattdm Dec 16 '15 at 19:11
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    Please do remember that sharpness is only one aspect of "how good a lens is optically". See What characteristics make a lens good or bad? – mattdm Dec 16 '15 at 19:46
  • Sharpest at the center? Sharpest at the edges? Sharpest at f/1.4, f/1.8, or f/2? Sharpest at f/8? – Michael C Dec 18 '15 at 3:56
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Generally, if you're talking about across-the-frame, has the higher line on MTF charts, test-chart type sharpness, then telephotos and primes will tend to beat out wider lenses and zooms--particularly in the corners.

That doesn't mean you can't find individual cases where that doesn't hold true (e.g., Canon's EF 70-200 f/2.8L IS USM II can pretty much hold its own or beat the EF 135mm f/2L USM on test charts).

So, my vote, if given this list as a hypothetical, would be the 85. But it would also be very very far from my first choice for a streetshooting lens--especially on a crop body--because sharpness ain't everything. How a lens performs with test charts, and how it performs in your hands are two different things. And what many newbs, seduced into the endless rounds of hairsplitting spec-poring test-chart pixel-peeping online discussions don't get is that sometimes sufficiency is more than enough.

You don't need the sharpest lens evah to get a great photograph. You just need a good lens and a decent amount of photographer skillz/imagination/vision.

Overall, while I commend your curiosity about lens performance and focal length, I'd also say that you're analyzing the which-lens-to-buy question from the wrong point of view. Image quality is fine and well. But cost, size/weight, usability, field of view, stabilization, focus speed/accuracy/performance, and build quality could take equal precedence in your deliberations.

For street shooting, I'd go with a 35 to 50 equivalent fast prime, because when I street shoot, those are the "most comfortable", most discrete, and best lenses for the way that I shoot. And I know they'll typically be sharp enough for my needs and print sizes. So, if I were shooting a crop dSLR, I'd probably go for something like the EF-S 24mm f/2.8 STM (pancake lens!), or 35/2 of some persuasion. But that's me. You're not me.

What you need, afford, or may find important as a lens feature can and will differ from my priorities. But it's always a group of factors, not just sharpness, or bokeh, or whatever the current hand-wringing fetish of anguish on DPReview is these days :).

  • I'm aware that sharpness isn't the only thing you need, as other factors may also bokeh, weight and price. For some systems like Sony Full frame, you're quite limited there on choice but as they say, you pay for what you get. That being said, saving a penny isn't bad too. – unsignedzero Dec 17 '15 at 0:26
  • In the context of registration distances of systems developed for 36x24mm film, wouldn't the 43mm diagonal and roughly 43mm registration distance and the resulting simplicity of design allowed for focal lengths near that distance give the 50mm focal length an advantage over the 85mm focal length? – Michael C Dec 17 '15 at 3:22
  • @MichaelClark if we're talking less need for correction, yes. But. Look at the MTF charts for the 50/1.8 STM vs. the 85/1.8 USM. – inkista Dec 17 '15 at 20:11
  • The problem with that comparison is that the 50mm f/1.8 STM is a low end consumer grade lens and the 85mm f/1.8 is an older design that was aimed at a higher market segment at the time it was designed. The 85mm f/1.8 is also considerably more expensive than the 50mm f/1.8 STM. – Michael C Dec 18 '15 at 3:44
  • Both the EF 50mm f/1.4 and even the EF 50mm f/1.2 L (with its intentionally uncorrected spherical aberration) compare much more favorably, especially above f/2 if we're talking about corner sharpness, to the EF 85mm f/1.8 than the EF 50mm f/1.8 STM does. They're all practically the same at the center at any aperture. – Michael C Dec 18 '15 at 4:03
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You surely need to look at some actual lens tests for the specific lenses of interest, like http://www.photozone.de/

Not sure it is a meaningful question, for example, a telephoto magnifies the subject, and makes detail much more obvious (85mm shows 3.5x larger than 24mm), when it may be too tiny to see in a wide angle. But it is not the same view, at least not from the same distance.

Wide angle will be worse than telephoto about distortion and vignetting, simply due to the wider spread. But if you need the wide angle ...

  • You can however, zoom with your feet. It may not always be possible, for example if you are in a room but can be an option. – unsignedzero Dec 17 '15 at 0:33
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    "Zooming with your feet" changes the camera-to-subject distance and therefore alters the perspective of the photo in a way that changing the focal length and shooting from the same distance does not. The shot you can get with a 24mm lens with a three-dimensional subject filling the frame will be markedly different from the shot you get with a 200mm lens and filling the frame with the same subject from a much greater distance! – Michael C Dec 17 '15 at 2:19
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I think it's folly to select a lens based on sharpness rather than focal length.

First pick a focal length that works for you. Then find a lens with that focal length.

The other way is just putting the cart in a different field from the horse, never mind in front of it.

Likewise even after you select a focal length sharpness is not even the second priority for street shooting. Not much point in having the sharpest lens in the world if it weighs so much and/or is so large it's not practical for your shooting.

For street I mostly prefer a zoom, but that suits my style. I do think modern zooms are excellent optically and if focal length is not your priority then consider a zoom. A kit lens is really surprisingly effective for street work, IMO. My own preference is a 28-105 equivalent and for most purposes that works well. That particular lens was picked because it's light, sharp "enough" and has adequate handling and a reasonably close focus. It's a balance of requirements. I tend to keep a small 50mm on hand as well, not for sharpness but on the off chance that I need a wide aperture or want a head and shoulder portrait or similar.

So maybe reconsider your objectives and priorities.

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50mm is the easiest focal length to design and manufacture. For a given price point I would expect the 50mm to be generally sharper.

  • Not always true, though. The Canon EF 50mm f/1.2 L, for instance, is designed to allow uncorrected spherical aberration to give it the distinct look it is famous for. It one of the most expensive 50mm on the mass market, but far from the sharpest at the edges. – Michael C Dec 17 '15 at 2:22
  • @MichaelClark Given that the 50L contains an asphere, I am extremely doubtful that the undercorrected spherical aberration is intention and not simply a limit of its design. – Brandon Dube Dec 17 '15 at 4:20

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