Even though I copied some old content from dredeman.com, this site is completely new, born November 1, 2021. I will continue to post English language Nikon related content here, mainly tech tips and reviews.
On www.quora.com, I got the request to answer this question:
|Adam Palmer and 1 other person are looking for an answer to:|
|Why does the 70mm end of my Sigma 70-200 F2.8 looks so much more zoomed in than the 70mm end of my Sigma 24-70 F2.8? They’re both full frame lenses being used in my Nikon D7500 APS-C.|
Here’s my answer:
Focus breathing plus accepted tolerance. The focal length is defined when focused at infinity. Yet all lenses with internal focusing change their focal length while focusing. (Zoom lens are almost always internal focusing, otherwise, they would need an enormous helicoid and get very large.) You have to imagine a zoom lens has a moving group lens elements for zooming, another moving group of lens elements for focusing and yet another moving group of lens elements to compensate for the focus changes while zooming (so to keep it sharp while zooming). I don’t know if you ever had two girlfriends or whatever at the same time (or whether your girlfriend or whatever had two you’s at the same time), but you can imagine that it makes things complicated. Same in a zoom lens.
In short: This means that the focal length gets shorter when getting closer. In the case of a 70mm that might mean it’s effectively 65 or even 60mm up close. It’s mostly not a big deal, it’s just one of the many consequences of lens design, which is one big tradeoff. Now I don’t know which Sigmas you are referring to, but the 24-70mm f/2.8 ART suffers from some focus breathing at the long end. Several iterations of Sigma’s 70-200mm f/2.8 too as far as I remember, and then also on the long end. So if you set both lenses to 70 mm, one will suffer from focus breathing a lot more than the other, since in one case 70mm is the short end, in the other, it’s the long end.
Another fact of life is that focal lengths do have some tolerances. 70 mm even at infinity, is never exactly 70 mm. It will more likely to be something like 67,6 mm or 72,4 mm. If your lens suffers from focus breathing, this is one of the ways to compensate for it, but sometimes it’s just the way a lens design turns out. There are also ISO tolerances here, so don’t start to measure your lens and hope to get your money back. And really, those are general things, all manufacturers basically have to deal with the same optical limitations in lens designs and then make their own tradeoffs.
If you own the Sigma Art, you will probably also notice the 24-70 is less sharp in the corners at 70mm. So keep that in mind and change to the 70-200mm while making pictures if you need the focal length and/or sharpness.
One last remark: the fact that you use a D7500, so an APS-C camera with those lenses, doesn’t change anything, as long as you use the same camera with both lenses. The camera crops the image 1.5 x but in both cases.
What can Tiger Woods do, you can’t? If you have to hit a ball and put it in a hole one foot in front of you, the difference between Tiger Woods and you might look small. But if you play a real game, and the difference is enormous.
A DSLR (or mirrorless camera) is a tool that enables you to make every picture you image, in the highest possible quality, at every possible moment. A smartphone is a tool with which you can make about 1% of these photos in a quality that varies between quite ok and very bad. (Quite ok means: looking good at the screen of your smartphone but just so-so on a 4k screen let alone if you want to do some post-processing to make contrast and colors look right.)
Yet most people make that 1 % of the pictures and don’t care to make better pictures. They don’t see that the faces of the people in the pictures are distorted, that their noses are much too long e.g.. If they would want to make really great pictures regularly (and not just now and then by accident) they would have to invest a lot of time in learning how to take pictures, even with a smartphone. And if you do that, why would you settle for gear that limits you to 1% of your capacities?
The very best smartphones are quite good – compared to smartphones from a couple of years ago. They took over large parts of the market for compact cameras. That was easy, after all, compact cameras use the same sensors and don’t have exchangeable lenses.
But physically smartphones differ a lot from DSLRs and mirrorless cameras. That has three consequences: 1. They’re extremely limited in lens size. 2. They’re extremely limited in sensor size. 3. They’re extremely limited in ergonomics.
Smartphone manufacturers have done a lot to compensate for this. The most important effort was in the field of marketing. That’s why many people ask this question. They don’t understand the differences, look at some pictures made with DSLRs but used in adds for smartphones and think they are almost equal.
The second important effort is that smartphone manufacturers spend a lot of money on smart combinations of extra hardware features and software, to mimic the effects of exchangeable lenses and larger sensors. That works – hence the 1%. But the differences are still enormous and one should never forget that those technologies triple down to mirrorless cameras (and to a lesser extend to DSLRs) so there will always be a large difference.
Maybe, one day, smartphones become as good as DSLRs and mirrorless cameras are today. Maybe, because with regards to lenses smartphones are already at the limit of theoretical capacities and the limits of the capacities of CMOS-sensors are also very near. It’s hard to say if and when smartphones become as good as DSLRs and mirrorless cameras are today, but it will, in any case, take longer than is relevant for the gear you buy and use in the next decennium.
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