Focus fine tuning indicative of lens defect?

[chuck]

I was testing the new 70-200 VR II against the 70-200 VR I. By reputation the VR II should be sharper. But using phase detection AF on

a new D810, I found the VR II is very soft at 200mm f/2.8, much softer than the VR I at same focal length and aperture, especially in the

center. When I changed from phase detection to live view AF, the VR II did much better, still not quite as good as VR I in the center, but

very close.

 

So I tried to use AF fine tune to bring the phase detection in line with LV AF. I found the amount of fine running required to match Live

View is appearently off the scale. The lens does get continuously sharper as one approaches the upper (positive) end of the AF fine

tunning scale, but never quite matching live view focus before running to the end of the scale.

 

So I will probably try to exchange the lens, although it is 3-4 days out of the 30 day BH return period.

 

But before I do that, does anyone see anything wrong in what I did to test and calibrate the lens? Is it common for LV and phase AF to

be different by that amount? Or is there some optical aberration resulting from a defective lens that can account for this difference?

[Ed_Ingold]

<p>There are manufacturing variations from lens to lens, including how the lens itself is calibrated. The chip in the lens can be reprogrammed by an authorized Nikon service for better tracking. Finally, the focusing sensor is located in the prism, subject to variations as well, which can be painfully obvious with a high resolution camera.</p>

<p>Lens calibration is quick and relatively inexpensive. It might be worth while to have the camera checked too. Some fine tuning might still be needed, but probably less than at present. You have a one year warranty on the lens from Nikon, up to three years if you complete the registration.</p>

[ShunCheung]

<p>I too have both versions of the 70-200mm/f2.8, and I have used two different samples of version 2. My experience is that it is a bit better than version 1.</p>

<p>With the lens on a tripod, manual focusing via live view should yield the best result. Regular phase-detect AF should be able to match that kind of result. If you are unable to achieve that with some AF fine tune, definitely exchange the lens for a better sample. Additionally, does that camera body work well with your other lenses? There are two sides of any AF issue: lens and camera body; both may have some contribution to any problem.</p>

<p>BTW, Nikon USA's (extended) warranty is 1+4 years. So you have a total of 5 years of coverage. However, you are better off exchanging your lens with a sample that is within specs than depending on repair service to get it back within specs. In case they don't get that right the first time, you may ending up sending it back multiple time, generating a lot of frustration.</p>

[chuck]

@Shun: Yes, the camera body works well with 70-200 VR I and 24-120 f/4 and 16-35 VR. There is no discenible

difference between LV and Phase detection AF with these lenses. 70-200 VR II is the only lens with this issue. I did

manually focus with LV, but the results were not discernibly better than LV AF.

 

@Ed: Thanks. But the lens is new, so I don't think I should have to deal with calibration to address this amount of

discrepancy. Also B&H will pay shipping to exchange this lens with another, so I will be sending it back for an exchange.

[ShunCheung]

<p>A bit of calibration/AF fine tune is perfectly normal. My 28mm/f1.8 AF-S needs -18 AF fine tune; with that, it is great. That is probably on the high side. +-5 or even +-10 is well within specs. If the amount of AF fine tune is indeed off the chart, definitely exchange for another sample.</p>

<p>Since today is Sunday and you can't ship the lens anyway, it probably doesn't hurt to double check that lens indeed needs so much AF fine tune. Sometimes one can overshoot and provides too much fine tune so that it still looks off, but from the opposite direction.</p>

[chuck]

I actually shot 2 complete sequences of 40 pictures from -20 to +20 value of AF fine tuning to satisfy myself I didn't miss a

sweet spot. The first time I let the phase AF do its own thing with each shot, so it didn't have to move much between

each shot. The second time I manually threw the lens out of focus before each shot so the AF has to work to find the

focus with each shot. The results were the same. It was clear the pictures followed a linear trend of becoming softer

and more out of focus towards -20, and sharper and more in focus toward +20. There wasn't a peak in the middle. At

+20 it still clearly wasn't as sharp as focusing with LV. So I don't think I missed the sweet spot. It looks pretty clear the

sweet spot, if any, is outside the range of AF fine tuning.

 

To be clear, the lens was not so soft that it was unusable. But with phase AF it was clearly not the sharpest lens in the bag even before

the tests. I was disappointed when I found it was notably softer than the 24-120 in at comparable apertures where the

range where they overlapped. So I decided to test it against the 70-200 VR I. The initial results were startling, to say

the least. If you blow up the picture to pixel peeping levels, the center the VR I was sharper by a big margin. With VR I at 200mm and f/2.8, you could make out features on a face about 3/4 of a mile away. With VR II the whole head appear to be a smudged blurry ball.

[Ian Rance]

<p>I asked about focus fine tune recently and after spending time doing it I feel that it is 80% the lens but also how it reacts when mounted on different bodies. Because the lens is focused wide open, the camera is focussing with the lens in its worst state (for image quality). With this softness the focus system of the camera must decide what is the best 'in focus' state and with the aberrations in the lenses of the AF system adding to the mix along with minor lens element misalignments (in the actual taking lens and the body) it is easy for errors to manifest themselves. I have noted that the very latest AF system in the D750 and D810 seems to be the most robust against errors - a little better than the D800. I would like to think that Nikon are understanding the technical issues and work to improve them on newer bodies. My D7000 was the very worst for AF error and despite battling with AF fine tune I could never get repeatable results. Sending it back to Nikon got it sorted in double quick time - for a reasonable fee. That was grey market too which I was told Nikon would not touch.<br>

To sum up I do think your lens has a fault so needs to go back for repair. I do think repair is often better than replacement in this instance.</p>

[rodeo_joe1]

<blockquote>

<p>"Finally, the focusing sensor is located in the prism,...."</p>

</blockquote>

<p>No it's not. The AF sensor is located in the bottom of the mirror-box. The RGB 3D matrix color (blah, blah, blah) metering sensor is located in the prism.</p>

<p>See here: http://www.digitalcameraworld.com/2013/11/01/phase-detection-autofocus-how-your-dslrs-af-system-actually-works/<br>

where there's a cross section of a D4 showing the location of the AF sensor.</p>

[chuck]

<p>I received the exchange 70-200 VRII lens from B&H on friday and tested it today. B&H went out of the way to get it to me by Friday. I would llke to thank them for it.<br>

With best manual focusing I can manage using LV, the new VRII lens definitely outperform both the VRII lens that I sent back for exchange (by a significant margin), and also slightly out perform the VRI lens (by a smaller margin). What is more, the new lens achieves its sharpest phase detection focus at AF Fine Tune 11, well within the range of the adjustment the D810 is capable of. The sharpest phase detection focus is very close to the sharpest manual focus, and contrast detection AF.<br>

The lens I sent back ran off the AF fine tune scale without achieving it sharpest focus using phase detection, and with the best manual and contrast detection focus it was not quite as sharp. It was definitely either defective or out of calibration.<br>

So I am glad I exchanged it. </p>