Best methodology for af fine tune.

[nathansanborn]

<p>I've had my D7000 for a few years now, and I find it to be a great camrea capaable of razor sharp pictures. I have determined that there is a strong possibility that I have a backfocus issue, specifically when using the 17-55 2.8G.</p>

<p>Often times when I was missing focus, it was due to operator error (focus and recompose not remembering that I had it set to af-c). But after more and more practice and better and better methodolgy, I keep finding soft eyes and faces with tack sharp details in the background, not really that visible on the previews on the camera back, but obvious in the images (even without pixel peeping). So I have many images taken yesterday for a client that are only suitable for facebook or 5x7. Luckily I was also using several other lenses that don't appear to have an issue, and photos shot at f7.1 with the 17-55 are very sharp, but at f4 not so much.</p>

<p>So my question, what is the best method for testing? I've read several previous threads and I have an idea, but when testing a zoom, should I select any particular part of it's range? The photo's shot yesterday were bad at 28mm and at full body distance, however before the shoot I did a quick test at home and found the focus to be fairly good, but that test was just shooting my keyboard wide open at 55mm only a few feet away and I couldn't see an issue.</p>

<p>I read Bob Atkins article linked from another thread, but it fails to mention things like subject distance or zoom range and whether or not it would change the results. I'm inclined to believe that it may based on my experience.</p>

<p>Thank you for your help.</p>

[nathansanborn]

<p>An example photo</p><div></div>

[nathansanborn]

<p>Selected focus.</p><div></div>

[nathansanborn]

<p>Face detail.</p><div></div>

[nathansanborn]

<p>Background detail. The plants and railroad tracks (wall) are much sharper.</p><div></div>

[ilkka_nissila]

<p>Focus targets are typically small and that can be a problem; they're designed to be used at really short distances which can render them invalid for photography at long distances. I generally find that if I fine tune a lens for a close distance then with many lenses the shots will be backfocused at long distances and more negative fine tune setting has to be used at these long distances. However, it depends on the lens.</p>

<p>I would use a focus target with suitable pattern as target and the associated tilted ruler to read the focus offset. I would as a starting point test fine tune settings from -20, -15, -10, -5, 0, 5, 10, 15 and 20. Turn the manual focus ring to offset focus before starting and then focus using AF-S mode. Take the exposure. Then turn the manual focus ring in the other direction and autofocus, shoot. Repeat this at least 3 times for each fine tune setting tested. Then investigate images in your computer and find where the point of sharpest focus is on the ruler. Plot the offsets in a scatter plot e.g. using Excel or similar program, and fit a line to the data points using linear regression. Find the zero crossing of that line and use it as your first order approximation of the focus fine tune setting for that lens. Then go out and do real world testing in various conditions to see if the focus fine tune setting needs to be adjusted slightly to account for the difference between the test target conditions and your real world conditions.</p>

<p>I use a distance of approximately 30 times focal length to do my focus fine tune chart testing, then I validate and adjust based on real world testing. I use Spyder LensCal but I don't think it's the best target. You might do a search on targets. There are even automated software+target packages which will apparently do all of this automatically for you! Sans the real world testing, of course.</p>

[bruce_brown]

<p>Nathan, also consider: <a href="

</p>

[rodeo_joe1]

<p>I'm not convinced that the issue lies with the AF system. The boots and socks of the woman are much sharper than her face, and this might be down to one of two reasons:<br>

1) Subject movement. I notice from the EXIF data that flash was used. The subject might have flinched and started to blink just as the shutter tripped. Try an inanimate object for your next focus test!<br>

2) Bad lens. I'm afraid this looks much more likely to me, since the plane of focus doesn't look vertical across the frame. If you look at the ironwork behind the lady's head it's well out of focus; yet the ironwork is sharply in focus at the bottom of the frame behind her legs.</p>

<p>I hope I'm mistaken in the diagnosis of a bad lens, but that image looks quite similar to those from a bad sample of a Tamron 28-75 that I had to send back a couple of years ago. A tilted focal plane isn't that uncommon and is caused by decentring of one or more elements. Unfortunately decentring seems to be a fairly recent and widespread blight affecting zooms and IF lenses, especially ones containing aspherical elements.</p>

[nathansanborn]

<p>Awesome guys, thank you! Do you find a difference in tune values across the zoom range of a particular lens, and if so, use the linear plotting to determine the final specific value for that lens?</p>

[nathansanborn]

<p>Rodeo Joe, I'm confident that it wasn't subject movement, as I had back focus across nearly every shot taken below f5.6 with this lens. Also the frames before and after had roughly the same posing and similar issues. It could have been me moving, but if 1/250 is inadequate to handhold 28mm I'm in serious trouble. Plus other shots in this series taken with an 85 1.8 at f4 1/125th are tack sharp.</p>

<p>You may be right about a tilted plane of focus. This lens was involved it a stumble I took walking in Puerto Rico shortly after I got it which caused the lens hood to crack and very slight scratching to the filter and end of the lens body, but it appeared to not affect the performance of the lens. But then again, I believe that I was often experiencing this issue before the spill and was attributing it to operator error.</p>

<p>Scratch that, looking to see if that may be the case, I looked closely at portraits taken right before my clumsy stumble and you can see how often the ears of people are just a bit sharper than the eyes. Not saying it is impossible, just saying the issue likely pre-dates my stumble. (17-55 is built like a Sherman Tank) Plus in the photo posted the iron work behind her head is way farther away than what is behind her legs, maybe 15-20 feet, the whole wall are a bunch of old railroad tracks placed in a super wavy configuration, really cool and I wish this shot would have turned out sharp (never mind the ups truck in the background, I was smarter at framing in the following shots).</p>

<p>I hope you're wrong, I'm just starting trying to make a living with my camera and don't want to be without this lens while it is in for repair. Which tells me that I should send in my 18-70 for repair to have a back up zoom in the event something does happen. (zoom ring stuck, fixed it myself, worked great, got stuck again, fixed it again, af issues now, decided to replace it with 17-55).</p>

<p>Really unfortunately about not using a moving target for a focus test is that this was not a focus test, this was a paid gig. The good thing is that I was aware that I may be having an issue with back focus (although I wasn't convinced until now), so I made sure to switch lenses several times and stop down farther than I normally would have often. Also on the good news side the client loved the shots, and I have a ton of good ones.</p>

<p>Hopefully a little af fine tune fixes it, otherwise I owe you a "you were right", delivered through a fountain of tears.</p>

[ilkka_nissila]

<p><em>Do you find a difference in tune values across the zoom range of a particular lens, and if so, use the linear plotting to determine the final specific value for that lens?</em></p>

<p>With zoom lenses I normally determine the optimal fine tune setting for both ends of the zoom range and then set an intermediate value for the value that I actually use, somewhere quite close to the setting that gives best results for the long end of the lens i.e. I consider the long end more important in this than the short end, but you will have to make your own decision about what to do in case there is a discrepancy between fine tune settings for the different the focal lengths ;-) </p>

[rodeo_joe1]

<p>Just for comparison; here's an example from that bad Tamron. It's easy to see that the lefthand edge is a lot fuzzier than the righthand side - in a streaky sort of way. This was from a lens that was supposedly brand new, straight from the box. A couple of years earlier I also had to return a new Canon L series 17-40 f/4 that showed one bad corner.</p><div></div>

[panayotis_papadopoulos]

<p>Some of the D7000 models had AF problems, mainly back focus. It has been discussed in the past here and elsewhere in the web. It's not a bad idea to get it to nearest Nikon service just to be sure. I haven't notice it myself for my D7000 for a long time, mainly because I was using my D300s, but looking one day at some pictures that my wife and I have taken during an excursion I saw that something was wrong with the AF. Tried different lenses but same thing...Just to be sure I took it to Nikon. Back focus problem was their diagnosis. They fix it and from that day and on my camera shoots like a charm, razor sharp.</p>

[Spearhead]

<blockquote>

<p>I had back focus across nearly every shot taken below f5.6 with this lens.</p>

</blockquote>

<p> <br>

Have you tested it on a tripod with a real test target? I find many of these so-called problems result from a lack of understanding of scientific testing.</p>

[daniel_bliss]

<p>If it's a D7000 I'd definitely have it looked at. The system as a whole seems to have had a lot of cases of AF mirrors being out of adjustment in such a way that they are positioned at the wrong angle. A telltale sign of this is if the AF is performing consistently in a different way from one color temperature to another, e.g. correct focus under sunlight, frontfocus under cloud and shadow (higher color temperature, more blue), and backfocus under incandescent light (lower color temperature, more orange). Alternatively, it may just be backfocusing everything, in which case I think it's actually an easier adjustment for the service center. For me, both bodies had the AF mirror angle problem. A word of advice; you'll get better results out of Nikon service if you do the sleuthing and process of elimination yourself and describe in detail how the camera performs under different conditions.</p>

[virginia_john_mybusiness]

<p>I found with my D7000 that I had very different focus points with my lenses and only one did not need some level of adjustment. I downloaded focus test images from various online sources and tried a number of them. I'm not sure that one source was better than another. What I did find out was that lighting and ensuring that the plane of the image being vertical and your camera the same during the test was important. It took about 15-30 minutes per lens, but was well worth the effort. There are a number of sources available on this site and others, as well as in the manual that came with the camera for undertaking this task. Once done, the difference is noticeable.</p>