Nikkor 24-70/2.8 front focus.

[mmene]

I just received a few days ago my new 24-70/2.8. It's a fact that it's a

superior lens with tack sharp characteristics, very low distortions and CA and

very good contrast and colors. Unfortunately I discover that their is a little

front focus problem, that I can calibrate it at D300 with fine tuning. I own

also D200 and I cannot do nothing about it. They tell me from Adorama that this

something common and natural and this lens is for D300 and D3 and not for D200.

Any advise please ?

[james_symington1]

That you can adjust for this kind of lens manufacturing defect with the D3 and D300 doesn't excuse Nikon, or Adorama for that matter, at all. Send it back and get one that works on all your Nikon cameras is my advice.

 

Good luck!

[ilkka_nissila]

Salesmen ... they'll say anything. Have it adjusted by Nikon, or return it for a refund. Too bad B&H doesn't have it in stock, and one has to resort to Adorama.

[jose_angel]

Michael, have you checked it at all distances and focals? I have also noticed a focus shift issue, in my sample it`s only at very close distances (+-1m); I cannot remember if at the widest or longest zoom end (probably the longest). At medium and large distances the focus is dead on. At first I used the AF fine tuning feature, but reached the conclusion after one week that it isn`t worth it. Sadly, I have deleted my test samples to save space on disk.

[elliot1]

I have the same issue with mine.

[mmene]

Thanks for your comments. Jose I didn't do a detail test at medium and long distances. I did it in close distance with f2.8 and many focal dist. The widest the worst. I will test it now at medium and long distances. What did you do with yours ?

[jim_orr]

Can you explain what is happening when it "front Focuses". Sorry if a stupid question. Maybe all mine do it and I didnt notice. Is it really noticible?

[mmene]

One example is when you make a portrait with sallow dof and you want to focus on the eye. Suddenly you discover the eye out of focus.

[jose_angel]

I have already found what I wrote at the time I did the test. I was so stupid doing a lot of shots, but on .jpg fine large to save time.

 

My conclusion was that other than the longest focal settings were difficult to test, it was only reliable from 50 to 70mm. The shortest focals were pretty difficult to distinguish. Also, my home laser-printed USAF .pdf target didn`t have enough quality for testing. I dislike to use that 45 degree angle method. I like to set the camera in front of the test target at 1, 2.5 and 7 meters, checking sharpness at different values (at 100% on the computer screen).

 

I think that I found somekind of badfocusing issue (between 10 and 20mm), at their longest focals (50 to 70mm) when focusing at a scarce one meter. At 2.5 and 7 meters, focus was dead on. Shorter focals were so difficult (almost impossible) to check under that conditions. I think that focusing issues at shorter focals (if so) could be mixed with somekind of softness dued to the short focus distance, thought.

 

I set the AF fine focus to +10mm and have used my lenses for a time (I was testing side by side the 17-55 and 24-70). I try to remember that closer shots at 55 to 70mm were sharper, but I was really afraid about misfocus at medium distances and infinity, but I didn`t check it. Then, I returned the camera to zero values, waiting for free time to perform a more exhaustive test. I`m still waiting to have this time!

[jose_angel]

Jim, if I`m not missing something, "frontfocus" means that the AF system catch the subject not where the subject is but (usually) some milimeters off closer to the camera. If so, the D3/D300 AF system allows to correct it setting a value between +20 and -20 on the camera (I`m not sure if this values are really milimeters).

 

If your camera "frontfocus", your head-portraits will be focused on the point of the nose even if you are placing the focus point at the eye level (image the subject straight in front of you).

 

It can be noticeable with medium to long focal lenghts at shorter distances, where there is a shallow DoF. Shorter focals hide this issue with their deeper DoF.

[jose_angel]

If I set the camera to "+10", I understand that mine is a "backfocusing" (not frontfocusing) issue, isn`t it? (I don`t have the instruction manual with me).

[mmene]

You are right Jose I calibrated my lens at +8 and it's OK. Thanks for all these useful information.

[ilkka_nissila]

If you apply the AF calibration, is the shift average for the whole lens? What about variability of the focus error as a function of focal length and distance?

 

There were posts in the B&H review section about front focus with this lens, and on dpreview at least one person wrote that they got it fixed by Nikon and now their lens works perfectly. I think this is something to consider.

[walterh]

I know you tested your lens on two bodies. The logical conclusion seems that the lens is at fault. This may not be so. The lens could be manufactured correctly and the two bodies might be slightly off. Two is a small number to draw conclusion from. Testing is better than assuming :-) In your case you might want to send both bodies and the lens for checkup. Without a proper optical bench or similar setup this is all speculation and technically completely invalid.

 

Another point is the question Ilkka raised. The focus point may not be constant for different zoom focal length settings. So setting the compensation in camera for one focal length may increase the error for another focal length. Unfortunately there is always room for improvement - even in the latest camera^^. The compensation should be possible setting a curve rather than a single value. Of course one might wonder how many customers would be able to follow the concept^^.

 

Since I am at this let me add another remark. The mechanical precision of all Nikon zoom lenses I had in my hand allowed for a (sometimes small sometimes very noticeable) slack. I am certain it will be explained to me that this is a feature needed for the AF operation and it is no a bug :-)

 

Since we talk about small deviations in AF accuracy I found in several cases differences in AF whether coming from the far end or the close end. For critical application like placing focus onto the eye lashes of a model when shooting a portrait this may play a role. Too bad we have only the D3 with a reasonable focusing screen among the digial Nikon bodies for MF to actually SEE the focus, at least in good conditions. By the way since the little computer in camera is so powerful today it could be programmed to compensate for the mechanical shortcoming of the AF directional focus finding.

[jose_angel]

You are right, Ilkka. I`m afraid, at least in my sample, that a correction for closer distances could be a drawback for the rest of focusing distances. That`s why I left the AF tuning on "0", at least until I could have a deeper test.

[ellis_vener_photography]

"They tell me from Adorama that this something common

and natural..."

 

no it isn't in my experience.

 

 

"...and this lens is for D300 and D3 and not for D200."

 

What a line of BS that is.

[mmene]

1) Of course I don't believe the dealer of Adorama. 2) I know that calibration differs by FL and distance and that's a big problem to calibrate it. 3) I am asking for a new lens but what happens if it's almost the same ? That's why I am asking for advises from owners of the lens.

[mmene]

Finally they changed my lens and the new one is superb. Thanks for your advises and comments.