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Archive 2016 · 24-85 focus way out of plane - send lens back?

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p.1 #1 · p.1 #1 · 24-85 focus way out of plane - send lens back?

I just bought a 24-85 3.5-4.5. I know, not the finest lens out there but I wanted something light enough for my wife or I to carry all day. It's a Nikon factory recon so 90 day warranty. I have briefly tested it, and have a concern I've never come across before.

So the edges are soft, very soft wide open, I was expecting soft edges but not quite this bad. Then I had a breakthrough moment and focused the center or corner of the frame in live view rather than focus locking on the center then pivoting the camera to put the same object at the edge for comparison. If you do this, the corner is acceptable, but the center is soft at the same distance.

So the edges of the image are not soft, they are OUT OF FOCUS when focus is locked at the same distance where the same object is in focus at the image center. In other words, the focus is not planar. Same deal with a flat object - corners out of focus when the center is in focus.

Looking at other lenses for the first time, it seems there are other lenses I own that have this problem to some extent, nearly all fast wide angles, but nothing like this bad. Also, the 24-85 shows this issue at 85mm as bad as at 24mm. My 85mm f/1.4 predictably shows absolutely none of this sort of thing even wide open.

Is this standard issue behavior for the 24-85 just because it distorts so much? Is this something that shouldn't be happening and Nikon could fix? Or should I just return to B&H pronto?

Oct 07, 2016 at 05:47 PM

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p.1 #2 · p.1 #2 · 24-85 focus way out of plane - send lens back?

Alright, since nobody has much to say, I'll follow up just in case anyone looks up this thread for info about this lens. Please correct the following if you have other info.

Yes, field curvature like this is within design specifications for this lens, especially at 24mm. The 24-70s and 24-120 VR are both probably noticeably better, but neither is immune. Even most wide AI primes have a fair bit of this. The problem seems to be worst at about 20-28mm where apertures can be fairly fast, and DOF is not huge as in superwide lenses.

Having used it a bit in the field, it's not as field relevant as I thought it would be. It really only affects the extreme corners severely and stopping down helps mitigate the issue. Importantly, this lens is sharp and contrasty in the center 2/3 or so of the frame.

I am still thinking about swapping it for the 24-120, Sigma Art 24-105 or Tamron 24-70, but all of these are twice the weight or close to it. The point was to have a lightweight lens to leave on the camera that others could use (rather than forcing the MF ring and shouting "it won't zoom"...) but would have acceptable quality. Coming round to it. Let me know what you think.

Oct 10, 2016 at 03:59 AM

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