[JJ_SO]

By adjusting in the lens, it would work on any body you connect it to, including those which do not offer body adjustment. Also the body based corrections are currently still quite limited. On the latest Canons you can set different adjustments for each end of the zoom range, but that's it.

Interesting to know for a Nikon user - here we do have only one setting.

 

The Sigma dock seems to allow you to set 4 focal lengths at 4 focus distances, which is much more comprehensive although finding 16 correction values doesn't sound like fun to me.

Actually, it's quite opposite of fun. But the results were worth it. Not to mention there were several firmware updates to Sigma lenses because some Nikon cameras behaved weird with the lens.

 

Practically, it's a boring job. Like you said, you need at least 16 shots, but I found it worth to do a bit more. Each focal length at each position: Three times the same procedure, bringing the lens manually out of focus, then let the AF work. Shoot and again the same procedure. This brings eventually missed AF positions out of the game. Most of the time AF was accurate, but maybe 5-10% of the shots were a bit off compared to the other two shots.

 

Then you need to change the lens from camera to the adapter and type the guessed results (which value I do have to use if the focus is 5mm off at 35mm fl and 0.6m distance? 2? 4? 1?).

 

After that, the procedure has to be repeated to make sure the values are accurate. After a while I noticed a kind of test-chart allergy. Not of the dock - of me. I know, there's a software for this kind of focus adjustments. And I know as well, there are a lot of possibilities to have a super-adjusted lens, extremely well adjusted body and still missing the right focus distance, especially if the object is moving.

 

Another thing worth to talk about is the question, on which spot the AF module actually works. Is it 50 pixels, 75 or only 20. Of course there are those little "focus frames" (talking about Nikon). But where exactly is sharpness happening? Stupid question?

 

Maybe. I just see the frames are the same, be it FX or DX. Putting a wide angle like the Sigma 18-35/1.8 in front of a D7100, this little focus frame square covers a comparatively big area. No problem if it's a brick wall. Big problem if it's something with depth, if you want to have a sunflower in 5m distance sharp and there is on each side of the sunflower enough space for another one or two. Which will be sharp? The one I focus manually with LiveView for sure. But the one I focus with phase detect AF is like throwing a handful of water. Something will get wet and not necessarily what I was aiming at.

 

So the adjustment of the 18-35 was time consuming and not as much an improvement as the adjustment of the 35/1.4 on FX was. Maybe this lens has very small tolerance abbreviations, maybe it's just because wideangle lenses are very difficult to adjust, the DOF is a bit too big and the testcharts start becoming too small.

 

But what if one uses different bodies? I don't know. I figure, it's the best way to adjust the lens with the body you use most with it and for the other bodies use AF-finetune of the body. The lens might have different correction values depending on the distance. By equalizing those you can get an ideal lens which is far easier to finetune to the body.

 

And what, if you have a mixture of bodies with AF finetune and without? Question is, would you really finetune a nice, new lens with stunning resolution values to a either old or cheap body without AF finetune? Are there much contemporary bodies out there without AF finetune?