D7000 AF Tune-age and Back Focus

Ever since owning the D7000 and in particular using the 17-55mm f2.8 lens I have suspected that there may be a focus issue or misalignment, I did correct this on the lens fairly earlier on but did not do a proper focus check (ie tripod, chart etc) until recently, at which time I thought I would do most of my AF lens. Note you can also MF lens but would need to use the default option I guess – this would particulary useful if you relied heavily on the focus indicator when using MF lens and the lens/body was out by a fair bit.

So first thing first, focus charts, there are a few freebie ones out there which you can download with varying levels of contrast and details, however these are all simple flat paper ones where you simply place the chart on a angle and focus on the contrasty bit. I did this originally but found to be a bit hit and miss since you are focusing on something that is on a slope which was/is a bit inaccurate, a contrasty item perpendicular to the lens would be a much better idea. Now, with most good ideas, of course someone has already deisgned and manufactured one – Datacolor Sypder people have a SpyderCal (from memory), this is a trick device with levels and tripod mounts and retails for at least AUD80, yep 80 bucks…no i am not spending my dosh on that…

A far simpler option and cheaper is to fabricate your own, it ain’t rocket science and unless you get paid solicitor rates you will come out ahead if you can do it in half an hour 🙂

All I did was bend up a bit of 0.032″ thick aluminium and take a corner out to hold the ruler and/or chart. I did size it up so my typical angle would be about 25 degrees. I did up a contrasty square to focus on (in a trusty cad program, but paint would work just as well) and stuck that to the vertical surface. I stuck part of a chart on the flat bit of AL and stuck a ruler next to that, ideally you would get the vertical face to line up with a major graduation on teh ruler, however that is for MK2. Cost, 30 minutes of my time.

The D7000 has the AF tune feature, basically it has a default value, this is applied if a unrecognised/unsaved CPU chip lens is attached, contrary to what I intuitively thought, which was that it was a global default value applied to all CPU lens (and hence the saved value on top of that, that would be nice since you could get 40 units of adjustment). It has a saved value for each lens attached (up to 12 lens) which does not get applied until you make some AF tune adjustment (you can apply zero to get to be listed). The saved value gets you plus/minus 20 units adjustment where minus brings the focal plane towards the camera. I do not know if these relate to a actual measurement, it would be nice if they did, would make it easier to adjust.

So onto the actually results and the interesting part.

Two of my lens, the 17-55mm and the 28mm  f2.8 maxed out the available AF tune at minus 20, with the 28mm f2.8 needing still more adjustment, pain in the rear I say.

All lens typically back focused with the exception of the 300mm and 50 1.8. The 50 1.8 is interesting since I never felt I got sharp results with it on the D80, however the 300mm was always sharp on the D80. I guess the next thing is to check all the lens on the D80 and see what that presents. I reckon that will show up two extremes of nikon tolerances.

Here is my list of lens and their AF tune values, all this leads me to believe that my D7000 is on one end of the manufacturing tolerances with it typically back focusing.

17-55mm f.8 – minus 20

55mm f2.8 – minus 5

11-16mm f2.8 – minus 7

18-200mm f3.5-5.6 – minus 15

50mm 1.8 – zero

28mm f2.8 – minus 20 (and still needing more)

300mm f4 – zero

300mmf4 + TC1.7II – minus 12

So here are a couple of shots of the 17-55mm – Note the focal plane is on the 122mm mark

The first is no adjustment and the crop

The next one is with minus 20 adjust and the respective crop

So here are a couple of shots of the 28mm – Note the focal plane is on the 122mm mark

The first is no adjustment and the crop

The next one is with minus 20 adjust and the respective crop

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