BboH Loc: s of 2/21, Ellicott City, MD

Have Nikon - Nikon has a menu function in many of its DSLR models - "AF Fine Tune" that is, in my words, used to offset front or back focus "errors".

Thinking about putting it to use and did some research.
...number of articles touting its use
however
...Thom Hogan states in his "Complete Guide to the Nikon D3" that "you are only making an adjustment for the focus distance you tested". And, with a zoom lens only for the mm the lense is set to test as only 1 setting per lense is allowed.
...Nikon manual states that "The camera may be unable to focus at minimum range or at infinity when AF tuning is applied.".

Given these caveats it strikes me that this feature is of very limited use which is only when extremely precise focusing is needed under controlled conditions.

However, given this feature's availability in various models I figure I must be missing something but I'm darned if I can figure out what. Will somebody please tell me?

greymule Loc: Colorado

Good question.

GeneS Loc: Glendale,AZ

It works great on my Prime lens,zooms not so good

saichiez Loc: Beautiful Central Oregon

My perception of Front or Back focus is that it is more often a physical condition where the tolerances built into the equipment are creating the problem.

A camera body can be at one end of the tolerance scale for the lens mount distance from the sensor. A lens can then be at the other end of the tolerance scale for the mount. This can create a stacking effect on the tolerances, putting the combined unit at twice the allowable tolerance for the combination. Hence creating an out-of-focus situation for THAT lens with THAT camera body.

Most times the camera and lens are sent to the manufacturer and calibrated to each other, once the inability to focus properly is tested and established. I do not think, however, that one could perform this action with a Camera Body from one manufacturer and a Third Party Lens. One of the down sides of going cheap and using third party lenses, and a common answer for more POS reviews on third party. With third party, one is simply not paying enough for the lens to cover consistent high Quality Control.

So, with third party lenses, the "occasional" great reviews read for them are more likely "Happy Accidents", followed by a declaration about the lens phrased... "Oh 3rd Party Lens, Me Love You Long Time!!":mrgreen:

I wrote a rather lengthy explanation (as I understand the problem). It was posted yesterday on a Thread that was title Am I Crazy. It was a situation where a Camera with two identical lenses, both same MFR was giving differing result.

Now, using third party lenses may create this problem more than same MFR lenses, because third party lenses often do not have as tight a tolerance requirement as the OEM. In addition, we all know that the lesser price of third party lenses is most often due to lesser Quality Control on the tolerances in any event.

Now in regard to your question, I am not sure how computerized fine tuning in the camera operates, as I doubt it could manage the distance of the lens rear element to the sensor, but perhaps that is the case. I do know manufacturers are incorporating this fine tuning into the camera.

If you go back to film days, to get the proper film to lens distance, plus the proper element to element distance in the lens, lenses and camera mount, a camera technician would often "shim" the various pieces for distance.

It's very unlikely that in "mass assembly line production" that the problem of lenses and cameras that were always properly calibrated was overcome.

In fact the problems with "front focus" and "back focus" in current cameras prove that the problem of calibration of all the pieces has not been resolved.

Furthermore, with more people using TeleConvertors than ever before (mostly wildlife and birders), there is also the problem of "stacking" those tolerances, multiplying focus problems.

It occurs to me that if people are not seeing a resultant correction of the problem, then the software solutions in the camera still have a ways to go.

I am not surprised by the comments of Thom Hogan and others, as it seems that the real problem in a lot of focus situations is a mechanical adjustment of the camera mount/lens mount reference measurement.

I have sent various digital cameras along with the lenses to manufacturers to correct back/front focus issues. In one case I send two lenses and a body in and they all required adjustment.

Perhaps a 25% increase in the price of all this gear.. Camera Bodies AND Lenses would create enough income for the manufacturers to "get it right" before shipping it.

It's not that difficult to test a camera/lens combination for front/back focus (one or the other usually). In the cases where I sent gear in for adjustment, I proved to myself that the combinations were not able to focus properly.

I'm hesitant to believe that software in the camera can resolve that problem as well as a proper physical calibration. :mrgreen:

BboH Loc: s of 2/21, Ellicott City, MD

Saichiez
Just about all that you said I came across in the look-see I was doing in preparation for the exercise; you summed it up nicely. Adding to Hogan and the Nikon manual, what prompted my question was reading the experience a gentleman on another forum reported - two zoom lenses tested at each mm setting with no consistant adjustment - each mm had a different + or -. My summation of his posting was he saying "What's going on here?". Seeing that, it struck me as the exercise would be just that - an exercise with no practical every-day use.

BboH Loc: s of 2/21, Ellicott City, MD

Gene
Can you discern the effectiveness at various distances from your subject? Or, would you say that with the prime lense the variation at various distances is so slight as to be unnoticible?