Nikon 24-70 f2.8 focusing issue... or D800?! Help!

DannyNorth

DannyNorth

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Hey All,

I have a problem with my AF-S 24-70.

When I zoom into 70 focus, then zoom out to 24 the focus shifts. I just sent it to repair to Fixation, but it's come back doing exactly the same thing.

The focusing at 24 (without zooming to 70 first) is sporadic as well. Very frustrating.

Take a look at these example. Straight RAW, with default settings/sharpening (25 / 1)

http://jpegbay.com/gallery/001784959-4.html

Any suggestions for what this issue could be? I'm going to take it back to the shop on Thursday, it would be ace to have an idea why I'm having this issue before I do!

I should add that I hired a 24-70 the other week that seemed to have the same issue, so I'm also paranoid it's my camera, though it does the same thing on the D800 as well as the D3s.
 
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For a zoom to stay in focus throughout it's range it needs to be "parfocal", whilst this is critical with cinematic lenses, it is less so with 35mm lenses as the auto focus will compensate for the slight focus shift that occurs.

I doubt that many 35mm zoom lenses are parfocal, as it is a more complex (and costly) design, you may find that the issue that you describe is normal, and not a fault with the lens.

I may be wrong, and stand to be corrected, as I do not have the lens in question to confirm this.
 
Martyn... said:
For a zoom to stay in focus throughout it's range it needs to be "parfocal", whilst this is critical with cinematic lenses, it is less so with 35mm lenses as the auto focus will compensate for the slight focus shift that occurs.

I doubt that many 35mm zoom lenses are parfocal, as it is a more complex (and costly) design, you may find that the issue that you describe is normal, and not a fault with the lens.

I may be wrong, and stand to be corrected, as I do not have the lens in question to confirm this.
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Yes. In the pre-AF era it was quite common to focus at max zoom for greater accuracy and then pull back for framing*.

It was always a dodgy practise IMHO but doesn't work with most zooms these days. No need to anyway as modern AF systems will nail it very accurately.

*Edit: I have a Nikon 24-70 on loan ATM and focus is way out if you do that!
 
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I have a 24-70mm and my lens does this but it is exactly what I'd expect. My 70-200mm is the same. Like Martyn said, you need a speciality lens to be able to retain focus while zooming. If you have the camera set to continuous focus then it may auto adjust during the zoom but if you have it on single focus then I wouldn't expect it to.
 
It's odd, because up until recently it would perform this task perfectly. I also have the Nikon 70-200 vr f2.8, and if I zoom into 200 focus and zoom out to 70 to take the shot, it stays in focus perfectly.

But as I say, it used to do this perfectly before. I've had the lens for 4 years, and never had this issue before.
 
DannyNorth said:
It's odd, because up until recently it would perform this task perfectly. I also have the Nikon 70-200 vr f2.8, and if I zoom into 200 focus and zoom out to 70 to take the shot, it stays in focus perfectly.

But as I say, it used to do this perfectly before. I've had the lens for 4 years, and never had this issue before.
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A quick search around the web would suggest that the 24-70 is not parfocal, but is a varifocal zoom lens.

Here is a link to a thread on Fred Miranda discussing this LINK
 
Hey Martyn, thanks loads for the link. You learn something new everyday!

Seriously, if what you say is true, I just don't understand how I could not ever have noticed before, especially owning the lens for such a long time and using it thousands of times! Plus, finding my focus in that way many times as well. Kinda dumbfounded.
 
DannyNorth said:
Hey Martyn, thanks loads for the link. You learn something new everyday!

Seriously, if what you say is true, I just don't understand how I could not ever have noticed before, especially owning the lens for such a long time and using it thousands of times! Plus, finding my focus in that way many times as well. Kinda dumbfounded.
Click to expand...

If it was parfocal i am sure Nikon would make a big issue about it on their website, and they don't.

I suspect that it is similar to my 17-55 in that it focuses so quickly you never really notice, I expect in the past that you were probably refocusing without realising.
 
If you were to ask this about Canon version, the answer is that they easily get out of calibration. When they are good they are nearly parfocal but can become very unpredictable. I could only guess this is the same.
Try another new copy; repairs can be very much hit and miss if you really want it perfect (most (incl. technicians) don't even notice it or don't care).
 
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