My first impression with this new lens is that that cannot possibly be true, when using this lens. As the f-number decreases, so does the depth of focus, making it extremely difficult to minimize spherical aberration, axial chromatic aberration, astigmatism and field curvature. viewfinder use) is actually more accurate more consistently than contrast detection (live view). I'm lusting after this gorgeous looking lens but I've read a number of comments from people who have had AF issues (back focusing, front focusing, focusing incorrectly at 18mm, 20+ of photos turn out to be out of focus, etc), and the problems seem to be worse with some cameras (canon.) than others. In all my past experiments with focusing I’ve found that phase detection (i.e. So even fully adjusted, a good third or more of the shots have the ears in focus instead of the eyes.

Relative to that, the random shot-to-shot focus variation is about four units. That -8 makes the difference, in a typical two metre portrait distance, between someone’s eyes being in focus and the back of their head (and 35mm f1.8 means that’s a big difference). It’s only because I discovered that there was a strong back-focus in general, while just playing with it, that I realised I’d have to do something about it. In fact, I didn’t actually intend to run this calibration to begin with it all. I do have a Nikon 50/1.8G but I’ve never tested it in the same way (because I’ve never really had any issues in practice). This lens isnt specifically built for macro, with maximum magnification of 0.23x and a minimum close-focusing distance of around 11 inches. This could be the same problem that was seen in reviews of the Canon version of this lens, or for all I know it could just be normal variation for this kind of lens (i.e. I also discovered that there is substantial shot to shot variation in AF accuracy. Its just as responsive as my Canon 17-55 mm f/2.8, meaning I didnt feel slowed down at all, despite the. It’s also annoying how huge the jump is from 0.5 metres to infinity, which is basically your entire practical working range, and it does feel like the necessary adjustments for true infinity are substantially different to those for two metres. In terms of the speed of auto-focus, I had no worries.

On the upside, the latter at least means that small calibration errors don’t really matter. Calibrating for infinity is particularly difficult, both because it’s difficult to find a suitable target that is that big, and because the depth of field is very high at great distances. It took a good two or three hours to arrive at these settings, using a variety of home-made focus targets. And some comments on the process.Īs you can see, on my particular D5200 it has an overall tendency to back-focus (negative adjustment values mean “the subject was closer than AF thought”). Just thought I’d share what my AF calibration settings are, at least initially, for the Sigma 18-35/1.8 on a Nikon D5200.

Sigma 18 35 canon review focus issues