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Autofocus with Sony NEX-7

Jeff K writes:

I'm reading your posts about the Touit lenses with a lot of interest. Thanks for doing such an awesome job posting photos. You've for sure got the best NEX 7 plus Touit photos on the web at this time. I've got my 32/1.8 on order.

I'm noticing that you keep complaining about the autofocus accuracy of the NEX 7 and I'm wondering why you are using AF with totally stationary subjects when you've got one of the best manual focus machines ever made in your hand.

The EVF with magnified view and focus peaking is much more accurate than AF with any Nikon or Pentax DSLR I've ever had and one of the things I love about the NEX is being able to nail focus 90% + using the magnified view and focus peaking. Since you use Zeiss lenses on Canon and Nikon DSLRs, you're obviously used to MF, so try using it more with the NEX and I think you'll be very pleased.

PS - when taking photos of people, AF with Face Detection mode on my NEX 7 (I'm using my Sony 35/1.8 and 50/1.8) is fantastic.

DIGLLOYD: Over the years, I’ve written so extensively about how much I like an EVF and how critical focus accuracy is.

I was in NYC for less than 48 hour from stepping off the plane and getting back onto it, and that includes sleep and the Zeiss Touit press event. I had very little time for ad-hoc shooting, no contemplative time to be sure. I needed to work fast and produce some decent images in a short time. Complicating matters, my kids gave me a nice 'bug' yielding a nasty sore throat the first night and I was not operating at 100%.

And so the reasons are simple:

  • I had zero experience with NEX-7 autofocus until I arrived in NYC, so I made the assumption that it ought to perform well under these easy-as-pie scenarios. Which was a bad assumption. I normally would not make such an assumption, but time pressure suckered me into it.
  • When there are 15 minutes of really good light in the evening, one shoots fast if it’s the last good light of a short trip. Hence I used autofocus; I had not even had time to review the prior images to realize how prone to error the NEX-7 autofocus is: so many shots were degraded by backfocus. The partial saving grace is that a somewhat stopped-down lens on APS-C has more DoF than full-frame.

The NEX-7 sensor quality is fabulous, but at this point, I consider autofocus on the NEX-7 useless for any critical work (frequent backfocus), at least with high performance lenses where even small errors are manifest even at ƒ/5.6. I look forward to seeing a future 24MP or perhaps 32MP NEX with improved autofocus.

In short, I would take Jeff K’s question and extend it this way: for professional work (reliable and consistent results), the Sony NEX-7 is best used as a manual focus camera with magnified view in the EVF.

As far as face detection: I don’t want the face in focus, I want the eyes in focus. The eye of my choosing, as often it is one or the other, even at ƒ/5.6. I put that focusing spot right on one eye (many times), and the NEX-7 screwed that up (many times). So I see little reason to believe (without testing) that it can perform better with face detection: will I get sharp lips, nose, eyes, what?

Below, I wanted the leading eye in focus. The NEX-7 backfocused by an inch or so. It’s just adequately sharp, but not sharp where I wanted it: the leading eye is slightly blurred, and this is at ƒ/5.6! What would face detection have done here? Maybe it has some magic, worth a try I suppose, but when I put a specific AF point on an eye, I should get razor sharp focus, as with the Sigma DP Merrill spot focus sensor. The NEX-7 just cannot do that. And EVF zoom is problematic with non-static subjects and having to reframe after focusing.

   Sony NEX-7 + Zeiss Touit 32mm f/1.8 Planar @ ƒ/5.6   
Sony NEX-7 + Zeiss Touit 32mm f/1.8 Planar @ ƒ/5.6

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