D7000 AF Tune-age and Back Focus

[biggerry]

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.

components


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




so, anyone else got any useful data on the AF tune? does anyone else here AF tune on any nikon body? if so what kinda values do you have.

[Jenno]

I think Mk11 should have some tastefull pink or red highlights to match your tripod
Otherwise well done.
Havent adjusted mine as yet

[ATJ]

I found I needed to fine tune my 200mm f/4D with my D7000. I found that +15 was the "correct" amount. I haven't checked my other lenses as yet.

[chrisk]

Very difficult to fine tune zoom lens. Primes are easy peazy.

[biggerry]

I think Mk11 should have some tastefull pink or red highlights to match your tripod
Otherwise well done.
Havent adjusted mine as yet

can I borrow that pink striped Polo shirt that I saw you in the other day to match some colours and get some ideas? Btw does your wife know you get around in strip pink polos?

Have you checked any of your longer lens? I found the UW's pretty hard to check.

I found I needed to fine tune my 200mm f/4D with my D7000. I found that +15 was the "correct" amount. I haven't checked my other lenses as yet.

hmm thats a fair whack, how does it perform on your D300?

Very difficult to fine tune zoom lens. Primes are easy peazy.

why thankyou for that insight so do any of your lens need correcting on your D300?

[chrisk]

Very difficult to fine tune zoom lens. Primes are easy peazy.

why thankyou for that insight so do any of your lens need correcting on your D300?

lol sorry, i didnt mean to be obtuse. i suppose what i was saying is how do you effectively fine tune a lens where the focal plane shifts ? are you tuning it at 17mm ? 35mm ? 55 mm ? if you fine tune it perfectly at 35mm, is that the consistently perfect fine tuning result at 55mm or 17mm ? how do you take focus breathing into account ? i think there's too many variables to get a good hold of it personally.

my first 50G was way out of whack and even at max fine tune was still a few mm off so i just exchanged it. i have no fine tuning on any other lens; partly cos im too lazy to check but mostly cos ive never noticed a problem.

[ATJ]

I found I needed to fine tune my 200mm f/4D with my D7000. I found that +15 was the "correct" amount. I haven't checked my other lenses as yet.

hmm thats a fair whack, how does it perform on your D300?

It seems to work fine on the D300, although I have never done any proper tests. Basically, I've had the 200mm for a couple of years and never noticed any focus issues with any of the shots I'd taken with the D300. I took a few shots with the D7000 and noticed they looked unsharp.

I did some testing with fine tuning on the D7000, not as scientific as yours but good enough to see what was what and what was better and found the +15 game me the best results. I then took some real shots at +15 and they were better than the earlier ones.

[aim54x]

I have never been bothered enough to check my lenses...but I do know that my 17-50 backfocuses on Alfred's D7000....

[Murray Foote]

Wot Rooz sez for zoomz. You can only really correct for one focal length.

Apart from a 14-24mm or 17-35mm, I shoot all primes. I tested them a while ago on D3 or D3s and didn't find a problem. I also found you've got to be really careful doing this sort of thing. If your methodology is imprecise, you can go round in circles finding false problems and creating false solutions.

Gerry, your methodology is much more high tech than mine. I just used two A3 pieces of paper and a couple of document holders.

[Remorhaz]

Very scientific (and industrial) of you... I don't suppose we could borrow your setup sometime and try on our own?

I've tried with the printed focus chart on the table method before and didn't notice anything abnormal (although I think that was back with my D90).

[surenj]

How in the world do you find the time???

Great write up

But tell me, is there only ONE millimetre focus difference between the 17-50 before and 17 -50 (-15) after adjustment??

[ATJ]

I just used a book at a 45º angle with the camera mounted on a tripod. I took a sequence of photos with the AF Fine Tune set at 5 point steps between the most negative and the most positive and reviewed which two had the best focus on the area where the focus indicator had been. I then stepped between the two best to get the right number.