More useful information regarding AF Fine Tuning.

http://photographylife.com/how-to-calibrate-lenses

@ golf007sd... nice video which I learned something again.... the distance from camera to target at which to do the AF Fine Tune is at least 50 times the focal length or for a telephoto lens at least 25 times the focal length. And adjust in small increments of 2 for the Nikon AF Tune scale.

http://www.youtube.com/watch?v=3JPTnz_mimo&feature=g-vrec

I calibrate the AF of all my lenses. For a zoom lens, the process can be extremely tedious because the optimal micro-adjustment will depend on the focal length you're using, the aperture or f/ at which you are shooting, and the distance from the camera to the target. Commercial products like Lens Align test for an AF offset at close and moderate distances, but not at large distances approaching infinity, which may require a different adjustment than the one that's optimal at the shorter distances (this I know from personal experience). To test my lenses, I use a custom designed target that is similar to an eye chart but also includes a good number of special characters with lots of detail, e.g., smiley faces are a good test of sharp/soft focus.

When I recently tested my Nikon 70-200mm f/2.8 VR II, 70-300mm, and 24-120mm f/4 lenses on my D800, each of them came out needing a -2 unit offset, independent of target distance. However, the sweet spot or optimal value of the micro-adjustment happens to be fairly broad, so a null value (no offset) turns out to be good enough. The 70-200mm and 70-300mm lenses mounted on my D7000 require different offsets, +3 units for the former, -2 units for the latter. Again, a null offset turns out to be good enough. My newly acquired 18-300mm lens mounted on the D7000 needs a +4 setting, i.e. it slightly front-focuses. For a while I also owned a copy of the 16-85mm DX lens. Wide open, it front-focussed by +4 units at focal lengths below 28mm but back-focussed by -4 units at focal lengths longward of 70mm for apertures wider than about f/7.1 . At apertures smaller than f/7.1 a null offset was optimal. Needless to say, this confusing state of affairs was difficult to keep straight in the field, and while I did take a number of really sharp pictures with the lens, I eventually got rid of it out of frustration.

Testing zoom lenses at large camera/target distances is fruitless at wide angle and problematic at the telephoto end of their zoom range. I've tended to use shots of high rise hotel buildings, which have lots of windows or other structure on their facades. Occasionally I'll use power and telephone poles instead. Some of the poles in my neighborhood have huge electrical insulators and fuses on them, which make good targets for AF systems, since they have lots of detail and contrast needed for a solid focus-lock. Perhaps others can suggest better choices than this.

I bought a 24-70 f/2.8G and a 50mm f/1.8G with my D600 two weeks ago. The 50mm has been unbelievably sharp... with focus being spot on. But, over the last two weeks I've noticed quite a bit of weirdness with the 24-70... a lot of shots look great with focus being spot on... and others are soft. I also don't think I've been getting the resolution I should out of this lens, especially at the edges (even stopped down, on a tripod, with a 3 second shutter delay things are a bit "smeary" toward the left side).

I was doing some (informal) testing over the last few days and I noticed that all of my shots at 24mm are heavily front-focused. I started dialing in some adjustment and noticed that I needed quite a bit (~7-10) before shots looked in focus at 24mm.

Today, I decided to get more scientific about it and set up my own "lens align" kit (also known as a vertical target with a yard stick sitting next to it at an angle). I started with no adjustment and shot at about 40mm... comparing contrast detect AF (i.e., AF in Live View mode) with phase detect AF (i.e. "normal" autofocusing through the viewfinder) using spot focus in the middle of the frame for both.

At ~40mm everything looked "ok" not much difference between the two autofocus modes. At 70mm everything still looked ok (a little front focusing but not that much). At 24mm.... it is totally off. The DoF _totally_ misses the target (yes, even at 24mm where the DoF is fairly large) using phase-detect ("normal") AF.

At this point I started trying to dial in the proper AF adjustment... and I settled on about +15 at 24mm! That is huge. At that setting things looked pretty good when autofocusing around my office though.

However, using this setting I then tried 70mm... and it back-focuses. Not a huge amount, but it is evident. Then I try ~40mm... and now the DoF at 40mm _totally_ misses the target... back focusing beyond the target. Craps.

I believe that something is actually wrong with the lens. This isn't a tolerance thing. I think that an element must be de-centered or something along those lines (de-centering would explain the lack of sharpness on one side of the image as well).

I'm not going to mess with Nikon on this one. This is a $2000 purchase that is less than 2 weeks old. It's going back to the reseller for replacement on Monday. I bought it online... now I'm wishing I hadn't (much easier to take it back to my local shop...)

I did this on a rainy day some time ago and found that the 85 mm f/1.8 did show some front focussing that I tried to correct using the AF fine tune. Two other lenses also seemed to have some front focus (it wasn't much, something like +5, so I was not sure if I did something wrong or not).

Finally I decided to send the camera plus four lenses to a Nikon Service Point while camera and lenses are still under warranty. According to the report the did a LWM adjustment (seems to be some sort of lens alignment) on the 85 and did the AF fine tune for the 28 mm f/1.8 (and I am sure that they did a better job than me). The other two lenses were ok.

Bad thing was, that I had to wait for two weeks and I did miss some nice weather for taking pictures...

@Golf: Ah, right - those figures in your link are for the 'proper lens sharpness' evaluation and not the AF fine-tune procedure - now it makes sense. Gotcha.

Hey, those are useful vids, I'll do it next time it rains.

Thx.

@spraynpray: These videos is where I got the info regarding AF-fine tuning.

http://www.youtube.com/watch?v=soPFToTnx9M
http://www.youtube.com/watch?v=PYeqYycLGAE&feature=iv&annotation_id=annotation_623717\

@golf - Although your link is interesting, I am still confused as to what relevance it has to AF fine tuning?

golf007sd said:
So question, given that I have two different bodies (D7000 & D4) once I have a lens (I may do this to all my lenses depending how much of pain in the rear end this all turns out to be) once I dial it on one body, can I use the same setting on the other? Or do I have to due this twice...one for each body?

Yep - the lens maybe correct and the body wrong. Or maybe you will find that the body is right and the lens is wrong. In that case you could send it in to be calibrated.

It's the combination of the body and lens that needs to be calibrated.

When you are done you will probably notice a mathematical relationship or pattern that will help you guess the number for the second body once you have it for the first for a new lens. Or at least it should be that way if everything is right...

So question, given that I have two different bodies (D7000 & D4) once I have a lens (I may do this to all my lenses depending how much of pain in the rear end this all turns out to be) once I dial it on one body, can I use the same setting on the other? Or do I have to due this twice...one for each body?

Just an FYI, Lensrentals rents the LensAlign 12 bucks for 4 days...

http://www.lensrentals.com/rent/calibration/lensalign

The link will get chopped but just search for LensAlign on the lensrentals dot com site.

(no, I'm not affiliated with them in any way)

I'm Ironheart and I approve this message

@golf - Surely one must always use the largest aperture to get the best view of the focal plane? Stopping it down may make it sharper, but it becomes more of a guess as to exactly where the focal plane is - or am I upside down on this?

@ golf007sd...thanks, I will most likely do the AF fine tune at the wider apertures as this is how I use the lenses....

This link might come in handy in helping those that chose to make fine tune adjustment to their AF system. Will make an attempt at doing this myself...but if not I will just wait till I meet up with Eric and have him show me how it is all done in person :P

https://dl.dropbox.com/u/82841586/Lens%20Sharpness%20Chart.pdf

yeah sounds about right.

but most people don't like the IQ degredation of the 2x nikkon one, the 1.4 seems to be what people use ( although of course you do lose the range)

So...if your lens had a max aperture of f/4 and you used it with a 2x teleconverter, at that point the D600 would still have the 7 center point available...but not the 33. Am I getting smarter? Or am I still off-base?

It means if you have a lens with a MAX aperture of f/8 wide open, the camera can still focus. It has no bearing on what aperture you set it to take the shot - all cameras focus with the aperture wide open and then flip the aperture down to the set aperture during exposure. (looking into the camera from the front with the lens off, that is what that little metal arm is for just inside the lens mount to the left)

Since people use long lenses with smaller apertures PLUS a teleconverter which further reduces the aperture, this is a handy thing, as the camera will still autofocus, albeit with less focus points than a larger max aperture.

This means lenses with a maximum (lowest F number) aperture greater than F8 wont auto focus, because not enough light comes through the lens. It has nothing to do with whether or not a lens will focus at a given aperture.

The new D600 autofocus specs read:

"Nikon Multi-CAM 4800 autofocus sensor module with TTL phase detection, fine-tuning, 39 focus points (including 9 cross-type sensors; the center 33 points are available at apertures slower than f/5.6 and faster than f/8, while the center 7 points are available at f/8)..."

What does the "33 points available at apertures slower than f/5.6 and faster than f/8, while the center 7 points are available f/8" mean? As a camera moron, it seems to imply that the camera won't focus at apertures outside that range...such as f/11.

I apologize in advance for my ignorance. Thanks!

Eric said:
@Correlli - It sounds like you are going to buy the commercial product. Here's a hint. When trying to align the vertical target with your lens, leave the lens cap on when aligning from the back of the target. That nice white Nikon on a black background is lots easier to work with than the open end of the lens.

Hi Eric, thanks for the hint, but I will not buy it. I was just curious which one you used. A friend of mine has got the Spyder LensCal and I will borrow it from him and give it a try.

Thanks for your posting Eric, it makes perfect sense and I will try it - at least then I will have one less thing to suspect when I or the camera/lens misses focus.

@ SkintBrit

I have not done the procedure yet, but definitely recognize the need. And, I made my own target. Fortunately I have a 60 foot long garage and will do this inside with no wind, on a tripod. The problem comes in several areas as I see it. Macro... clearly the small DOF will make sharp focus critical...portraits...getting the exact focus on the eyelashes, again at large apertures and small DOF, and with the long lenses, trying to focus on a helmut of a driver the small DOF agains requires precise focus. And, if done manually, no problem, but if the autofocus is used and running the focus to the incorrect point, yikes, no keepers...

So, I will get to this fairly soon as the checking and compensation of the errors drives me more nuts than I already am!

Hi all. Quick question, do you routinely run the focus calibration on your camera/lens combinations? I've never done it, and always been a bit scared to try, but do you all calibrate regularly? I presume the first thing I need is a way of checking wether I have any focusing issues, has anyone tried using a "Focus Pyramid"? Seem like a reasonably inexpensive way of highlighting any problems? Any thoughts?

P.S. Thanks Eric for your tutorial on how to actually go about checking and adjusting if necessary. I'm sure the info will come in very handy.