Problems with Sigma 150-600mm C AF on Sony A7rII

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decoder_oh New Member • Posts: 2
Problems with Sigma 150-600mm C AF on Sony A7rII

Hello all,

I recently purchased the Sigma 150-600mm Contemporary with MC-11 for my Sony A7rII. I upgraded the firmware for both the lens and the MC-11, then did several tests and found the AF to be quite inaccurate. Most of the tests I did were on small subjects that were about 10-12 meters away, taken on 600mm F6.3 and F7.1 either with a tripod and OSS off as well as hand-held with OSS on (with shutter speed 1600 to avoid any motion blur).

In both setups, I noticed that maybe in 20-30% of all cases, the AF was off. Most of the time, it wasn't totally off (that would be ok, as it is noticable), but rather slightly off so you only really see it when zooming in 150-200% and compare it to one of the shots where everything is properly sharp. I picked out one of the more subtle examples which are the most annoying because I might not spot them immediately:

Unsharp

Sharp

As I said, this is one of the more subtle examples, I've also had shots in there where it was already visible at 100% easily. The amout of AF offset seems to randomly vary with AF-S and with AF-C it seems to be worse. I also did some shots on a self-printed scale that is normally used to calibrate for back- and front focus on DSLRs. Same thing here, sometimes back focus, sometimes front focus, sometimes accurate.

Now my questions are:

1) Is this a problem with my lens, or am I just expecting too much?

2) Could it be a problem in combination with the A7RII which, according to my research, has some AF issues anyway and less fields for contrast AF control?

3) Would I be better off getting the Sony 100-400mm + 1.4TC instead?

Note that my primary goal for this lens was to take pictures of birds and (wild) animals. I don't like zoo photography a lot, I rather prefer to find wild animals.

Thanks in advance,

Chris

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