>What concerns me especially with zooms is that the environment >that LensAlign and FocusTune images are taken in i.e. almost >laboratory conditions. The real world is very different with >no fixed aperture, speed or even ISO or focal length (unless >using a prime, Where I get confused is where the two >environments cross. > >For example, I tested my 70-200mm f2.8 and it stated for 180mm >it required a fine tune of +15, whereas at 70mm it gave -5!. >So, I fixed a flat target ISO test chart and handheld at 70 >and 200mm. On checking the chart it was sharp as could >expect.
I don't know about your particular case, but one reason these tales abound is that some lenses have a relative flat response to fine tune.
Here's my 200-400 for example:
While there's a peak, the visual difference from the range of about -5 to +10 or so is really negligible, and more importantly is lost in the noise of focus inconsistencies (look at how the points vary on the chart). I'd have to get down to +15 or -15 to really get something visually wrong in the real world.
Now look at my 200/F2 on a D800:
Notice the sharp falloff. Even though there's a lot of variation in individual points(e.g. look at zero where it ranges from 1100 to 1300), there's a very clear difference. Here the "visually ok" range is more like +5 to +16 or so, both tighter and also shifted a lot.
I think seeing these curves helps to explain a lot of what people see. Lenses with a relatively flat response to fine tune "work fine at 0 on all my cameras, like it should" (as many have said). Some with more rapid falloff are less likely to look fine at zero unless by chance they and the camera all end up at zero. My D4 tends to be best negative, my D800 (post repair) tends to be best positive. So the 200-400 would be fine on both at zero, but the 200 definitely needs fine tune to be sharp on either one, and in opposite directions.