I had a chance to try both the Sigma 85mm and the Sony/Zeiss 85mm f/1.4 on an a77 a few times. For posterity's sake, I figured I'd post the conclusions:
- Sharpness: Both were very sharp. The sharpness was also very similar -- even in laboratory conditions, I couldn't tell the difference. A friend of mine claimed to be able to see a difference between the corners on full crop, but I think it was psychosomatic. Note this was crop sensor (reviews claim more difference on FF). Tossup.
- Focus speed: Almost identical. Disappointingly, the Sigma HSM was no faster than the Sony screw drive. Tossup.
- Focus noise: Sigma HSM creams the Sony screw drive. The screw drive grinds and clunks at the end. It's disappointingly noisy.
- Focus accuracy: Sigma required about +10 MF calibration. Sony was pretty good with no calibration. Sigma calibration drifted between shoots; you want to re-calibrate at the beginning of a shoot. Sony stayed pretty constant. Without recalibration, Sony was clearly better. With recalibration every time, Sigma won. Sony would give slight errors based on which direction it focused from, and Sony couldn't be perfectly calibrated -- minimum purple fringing happened at a slightly different place than maximum sharpness. Sony seemed to do ever-so-slightly-better in very low light. Overall, tossup.
- Support: Sigma has a 4 year warranty, and competent folks on the phone. Sony has a 1 year warranty, and you get minimum-wage idiots. Sigma will recalibrate AF microadjustment to your camera calibration free-of-charge during the four year warranty period as many times as you like; Sony will not do jack. Overall, Sigma creams Sony.
- Manual focus ergonomics: Sigma has a large, comfortable, smooth AF ring, and the body doesn't change size as you focus. Sony's is less smooth, but actually takes a bit less force to turn. On Sony, the lens also changes length, which is annoying. Sony has a greater swing (half-turn instead of quarter-turn), so fine autofocus is easier. Initially, I preferred the Sigma, but after shooting a while, I preferred Sony. Toss-up.
- Contrast/flare: Sony has colorful blobs. Sigma has a general haze throughout the image. Overall, I prefer the blobs to the haze, so for me, Sony is the winner, but it depends on what you want.
- Purple fringing: Similar between the two. Tossup.
- CA: Sony was probably slightly behind. Sigma.
- Color: Very similar, and I actually prefer Minolta colors (which are quite different). Tossup.
- Build quality: Sony is full metal, and looks well-built. Sigma is plastic and rubber. Probably Sony.
- Size: Similar weight, but Sony is smaller. Sony.
- Future-proofing. Sony has a screw drive, which Sony is hinting it might obsolete (LA-EA1 is incompatible with screw drive). Sigma compatibility sometimes breaks with older bodies. Tossup.
- Bokeh. Surprisingly similar. Tossup.
Conclusion: I was surprised, but it really was a tossup. For me, major upsides of the Sigma are the quiet focus motor, and the high quality support and warranty. The major advantage of the Sony is the better contrast with bright lights (I don't mind the colorful blobs as much). Given the price difference, the Sigma is clearly the better lens to buy. It looks like I can get a very good price on a used copy of the Sony, so I just bought that. Assuming that doesn't fall through, and it's a good copy, that's what I'm going with. If that sale falls through, I'm getting a new Sigma.
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