Potential AF Issue with AF-S VRI 70-200 F2.8

[avishek_aiyar]

<p>Hello,<br>

I wasn't sure what to make of the issue with my lens, so thought I'd describe it in detail and get your opinion. <br>

I bought of the copy of the lens on flea-bay almost 2 years back and have been quite happy with the lens with my D300 and D3. <br>

One "issue" I have had with the lens for the duration of my ownership is what appears to be quirky AF. I assumed the issue was intrinsic to the lens so never made too much of it. <br>

AFS is snappy most of the time. However, one issue I have noticed is when cycling between extremes (infinity to close focus) it won't always snap into focus. <br>

As an example, if I want to focus on an object which is ~10 feet away and I purposely defocus the lens completely before I try to AF, I basically won't get AF. In this case, what I need to do is do a partial manual focus and then the AF would kick in. <br>

Is that normal behavior for this lens? It hasn't been a bother for me at all, but I am trying to sell the lens and want to highlight this if it is a genuine issue to any potential buyers. <br>

Thanks.<br>

Avi</p>

[michael_bradtke]

<p>That is not normal at all. Sounds like there might be something up with the AF</p>

[pete_resetz]

<p>The AF system in all cameras including Nikon works on contrast detection. I have used a friend's AF-S 80-200 f2.8 D ED lens (non VR) many times and have had a simular problem. What I found was that the lens focuses so fast and if the camera's AF sensor has a low contrast object it will just hunt and hunt for something to lock onto. If you aim the AF sensor at an edge of something or something with detail, the AF has something to lock onto. And with that lens if I attach a 2x teleconverter which brings the aperture to f5.6, it slows the AF down to the point where it will lock onto something of low contrast. This did it with two Nikon F5's a Nikon F100 and a Nikon D1X. I dosn't do it with my Nikon D2Xs which has the next generation AF system. <br /> Your D3 and D300 are supposed to have an even more sensitive AF system, so if that doesn't work you might have a problem with the lens not communicating with cameras properly. You can also try cleaning the lens contact pins. I use a product called Power Pen. It's a non corrosive fluid that prohibits oxidation between electrical contact and has a dry lubricating property to it. I also use it on the camera's contacts. It's sold at retailer of batteries like Batteries +Bulbs.</p>

[eric_arnold]

<blockquote>

<p>The AF system in all cameras including Nikon works on contrast detection. </p>

</blockquote>

<p>that's not accurate. Most DSLRs including Nikon use phase detection auto focus (PDAF). Nikon explains this <a href="http://nikon.com/about/technology/life/imaging/hyspeedaf/index.htm">here</a>:</p>

<blockquote>

<p>Phase-detection autofocus is employed in digital SLR cameras. In this design, light that enters the camera through the lens is divided to create two images. This is basically analogous to how human eyes function. Our brain reconfigures the scene viewed by the left and right eyes to produce a three-dimensional image. The camera measures the distance between the two images and adjusts for the difference by moving the lens to obtain correct focus. This process controls the two images so as to determine focus accurately and move the lens position accordingly. Wasted motion is prevented for quick focusing.</p>

</blockquote>

<p>In any event, Avishek's issue doesnt seem normal. The D3 and D300 have the same AF module, so they should have similar behavior. AF-S (single shot) wont give focus confirmation unless it can lock on to something, but even from defocus, the AF should be snappy with that lens. If it's doing the same thing with both bodies, it's most likely a lens issue. if this issue is consistent in shooting situations where AF should work normally, i would have that checked out before selling it. </p>

[ShunCheung]

<p>It is not clear where the problem is, but the behavior the OP describes is definitely not normal.</p>

[avishek_aiyar]

<p>yeah...looks like my lens always has been "defective" and I never knew about it. :( <br>

Like I said, the AFS is pretty snappy most of the time. But when I start with a completely defocused image, it plays completely dumb! <br>

Thanks for clarifying this folks.<br>

Avi</p>

[pete_resetz]

<p>Erik Arnold.<br /> Yes you're correct about Phase Detection, but I felt that it was irrelevant to bring up seeing that it does the same with two different cameras. I was told by a Nikon tech rep, that contrast is part of the AF equation when I had contacted Nikon years back with my problem. So I can only go on what I'm told by the people that represent the product. So when I had applied that AF focus technique, it worked from that point on just fine.<br /> Also. There was a situations that I had experienced at a Best Buy with the new 80-400 AF-S VR, were if the VR is set to active, it would sometimes interfere with AF because the VR group of lens moving around in the lens. Might have been a bad lens, or me. I'm not the human bipod I used to be. <br /> I was just suggesting to Avishek to try everything possible first before spending money just to find out that there might be a simple solution.</p>

[eric_arnold]

<blockquote>

<p>that contrast is part of the AF equation </p>

</blockquote>

<p>that's true, and some newer cameras actually use hybrid CDAF/PDAF systems, like Nikon 1, Sony, Olympus and Fuji. but i do think we need to be careful here to distinguish between the technical term for a type of focusing system, and the process of acquiring focus, in which the total equation depends on things like light (EV) levels, discernible edges and 90-degree angles, contrast in targets, sensor sensitivity, aperture value, etc. Saying 'AF systems <em>in all cameras</em> use contrast detection' is a bit misleading as CDAF/PDAF have differing characteristics -- CDAF generally has more focus accuracy, but can be slower, while PDAF is better for moving images and low light. (incidentally, the fact that mirrorless bodies up until recently used CDAF-only is one reason they tend not to be as good at capturing Things Which Move, especially in AF-C.)<br>

<br>

To be clear, attempting to focus on a white subject against a white background (or similar low-contrast image) will trouble any camera and lens combo, but that doesnt seem to be the OP's issue here.</p>

<blockquote>

<p>Might have been a bad lens, or me. </p>

</blockquote>

<p>Active VR has slightly different characteristics than Normal VR, and in some cases VR can take a minute to "lock in" after focus is set. This effect is noticeable in the viewfinder. When i shoot with the 70-200 VRII, i've sometimes gotten soft images when i shouldnt have because i changed the focus point too fast, before VR kicked in. That's why you should turn VR off in situations where you don't need it, i.e. fast shutter speeds. An 80-400 at a big box store may have been mishandled, so we can't rule that out, but the Active VR setting is intended for use when your own position is unstable, like from the bed of a moving truck. <a href="http://www.nikonusa.com/Images/Micro-Sites/VR/experience/tips/normal_and_active/">Here's</a> what Nikon has to say about that. Also note that basic panning shots should be in Normal VR mode.</p>

[pete_resetz]

<p> Erik. <br>

True again in what you're saying. All I was trying to give was a simple answer for something for Avishek to try. <br>

As for as the AF-S 80-400, that could very well be miss handling. But I had the usage of the older AF-D 80-400 version with the screw drive about 12 or 13 years ago and it did that to me with the VR in Active Mode. And also about the same time period I got to use a AF-S 200-400 for a week with similar results. Each lens did it only a couple of times. This was with two F5's, three F100's, and one D1(the two F5's and one of the F100's were mine). Also the lenses had an odd habit of some of the images being a little soft on one side of the image. And again with multiple cameras. That's when I had contacted Nikon Tech Support about those issues and was told that with the VR system, the lens or lenses group located in VR assembly can be all the way to one it's axis limits when the shutter is released causing the VR,s lenses to be misaligned with the rest of the lens behind the VR assembly. Nature of the best. I don't follow Canon but I can speculate that there IS lenses could have the same malady seeing that Canon uses something similar. Interestingly with the Sony system I've read that there IS/VR is built into the camera body. </p>

[eric_arnold]

<blockquote>

<p>I had the usage of the older AF-D 80-400 version with the screw drive about 12 or 13 years ago and it did that to me with the VR in Active Mode.</p>

</blockquote>

<p>VR technology has improved a lot since 2004. So has camera-to-VR communication. if your most recent body is a D2X, you may not see the benefit of that, however. the problem of lens-based VR is, you're stuck with it for the life of your lens, or how long you own it. if it goes screwy, you have to either get it fixed or get a new lens. But as far as AF errors with certain lenses are concerned, they are complicated mechanical tools and if they get out of alignment, it's best to align them. The notion that a $1500 or $2300 lens could remain issue free throughout its entire lifespan may not be accurate or realistic. As a photographer, the only thing you can do is be aware of the characteristics of certain lenses and VR or AF performance. if you've been using this for two years and it hasnt impacted output, then maybe its not so bad. OTOH, if youve been aware for the problem for a while and have been putting off getting it checked out, please do ASAP. dont just dump a faulty lens on a buyer, at least without disclosing the issue. </p>

[elliot1]

<p>Which AF mode and probably of more importance which AF point(s) are you using?</p>

[Ed_Ingold]

<p>Sometimes AFS problems stem from a bad connection between the camera and lens. Fingerprints and dirt can be the root cause. Use an alcohol pad, available from any drug store, to clean the contacts. Lens cleaner and tissue would work too. Never use anything abrasive or that leaves particles. Especially never use a pencil eraser, which contains an abrasive (pumice). It will cut through the gold plating.</p>

<p>Real life is seldom that simple, unfortunately. Authorized Camera Repair in Morton Grove, IL will usually give you a free analysis and estimate for repair, short of a full round of testing. (There might be a nominal charge if you don't proceed with the repair, plus shipping). All of my Nikon f/2.8 zooms, including the 70-200 VR1, have been repaired. The 70-200 needed a motor and zoom cam, but it came back like new.</p>

[michael_bradtke]

<p>Two cameras same problem it is the lens. I had this problem with my 80-200 AFS. Unfortunately when I sent it in Nikon did not have the parts available to repair it. <br>

Your lens is new enough to make it repairable. Send it in and have it checked.<br>

In all my time shooting a DSLR in nasty environments I have never had issues with dirty contacts. </p>

 

[avishek_aiyar]

<p>Elliot,<br>

I typically use AF-S and and the automatic AF point selector. <br>

I am going to run detailed tests on the lens to document the problem in greater detail to confirm that it is a problem after all. <br>

Thanks.<br>

Avi</p>

[Ed_Ingold]

<p>Cleaning the contacts costs nothing and takes little time. Would you prefer to take each problem to Mr. Goodwrench or do a little trouble shooting on your own?</p>

<p>I have had several occasions in which it helped to clean contacts, and helped others as well. Most of the time the wiping action assembling the lens to the camera is sufficient, but not always.</p>

<p>That said, there is an expression in the electronics field that the most expensive circuit serves to protect the fuse. Cameras are no different.</p>

[eric_arnold]

<blockquote>

<p>I typically use AF-S and and the automatic AF point selector. </p>

</blockquote>

<p>do you mean area-focus AF? according to <a href="http://www.nikonusa.com/en/learn-and-explore/article/ftlzi4po/af-area-modes.html">nikon</a>, that mode is for "when there’s simply no time to select a focus point, or when using Live View in hand-held mode at high or low angles" ... i typically do not use this mode as it almost never selects what i want the camera to focus on. not sure if changing this will affect your lens' performance, but you could at least eliminate it as a possible source of your problem. </p>