Originally posted by CoreyC It may be unrealistic, but I do kind of expect that for the prices we're paying for the bodies and lenses that the tolerances should be a bit tighter and that an AF adjustment beyond +/-5 should be the exception.
If a fine adjustment is required, it is seldom an issue with the body* and even with the lens is not an issue of manufacturing tolerance in the normal way we might think of such. The usual causes are all optical and would include:
- Centering defect
- Longitudinal inconsistencies (element spacing) in focus or zoom groups
- One of more elements not properly set in place
Any of the above would create ambiguities of focus that may bias out-of-focus detection by the PDAF sensor. Often enough, the issue is worse at some focus distances and zoom settings than at others. Internal focus and zooms tend to be more prone to front/back focus problems.
As noted above, soft results, particularly with a high resolution sensor are more likely due to camera or subject motion, atmospheric conditions, soft lens, and/or allowing shutter release early or late to focus acquisition. Only if a repeatable pattern of clearly demonstrable front focus or back focus is present should a fine adjustment be done. Experience on this site has been that fine adjustment attempts often result in a lot of time wasted and owner frustration with no improvement in field results.
If you are using LensAlign + FocusTune according to directions and the software indicates statistically significant bias across multiple attempts (say 10+ minimum, half from minimum distance stop and half from infinity stop), that is about the best you can attempt without an optical bench. I am curious about your results:
Quote: D FA 24-70 at 24mm: +1
D FA 24-70 at 24mm: +10
D FA* 50mm: +6
D FA WR 100mm: +6
D FA* 70-200 at 70mm: ~+12 (AF Fine Adjustment maxes out at +10)
D FA* 70-200 at 70mm: +10
FA* 200mm: +10
What is does the repetition mean for the D FA 24-70 and the D FA* 70-200?
Steve
* It will present as all lenses requiring adjustment in the same direction at all distances and (for zooms) focal lengths. Even if mild, this type of issue is a defect in manufacture of the body and should be covered under warranty.