D800 focus with 1.4 prime lenses is very variable and inaccurate

Started Jan 20, 2013 | Discussions thread
Jim Keye
Senior MemberPosts: 1,597
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Re: Flawed tests
In reply to primeshooter, Jan 23, 2013

primeshooter wrote:

Pradipta Dutta wrote:

Shooting handheld at f/1.4 with a subject that has a child on his lap is certainly not a good test setup. Slightest of movement either by the hand motion or the subject will screw up the AF with a very-very narrow DoF.

I am not defending the AF module of D800. All I am suggesting is that you cannot prove anything with such a flawed test setup.

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Let me explain something to you that debunks your theory of motion between photographer or subject. EVERY time I use LV contrast AF detect I get better focus at f/1.4 on faces than PDAF. EVERY TIME. Now consider how long LV contrast af takes. At least 4 seconds in which time the subject could have moved metres out of that original focal plane. This is NOT a "test" or a test rig. You can't set up the camera on a tripod and test for this. It's an issue with human faces, not some test chart. The simple fact is the D800 should be able to focus on a face a few feet away at f/1.4 with consistency in 2013.

Whether it the AF should be able to or not is something we're going to have to set aside for the moment. (We all know the answer.) The more important question, far more important, is whether other people are able to achieve focus or not, and if they in fact are, why they are and other aren't.

Rayman's comments about "pat on the back" are oriented towards the fact that we're not seeing you take any steps to isolate the issue. No comparison with other bodies, no comparison with tests, no comparison with other shooters, no comparison with other techniques. (CDAF is not another technique, it's an entirely different way of focusing, and obviously not the preferred method in the scenarios you're describing.)

The problem with the internet is that you're almost always going to be able to find people who echo your experience, but that doesn't prove anything. The clearly out of focus by 3 feet examples posted learlier appear to be a bug of some kind. Is that isolated to a few cameras, to the AF firmware in general? There was a post by a different gentleman who said he had two clear examples of this at a wedding and all the rest of the time the camera was spot on.

Some people here seem to experience problems, and others don't. But that still doesn't tell us what's going on because they're not like-examples, not to mention not even all the comments are specifically about f1.4 primes. Some people claim the AF-C is jittery in low light, and yet other people don't seem to have a problem with it, jittery or not. (And the jittery issue makes sense--the camera is trying to be more precise (forcing the camera to reevaluate focus more often). Might this have something to do with trying to match it to 36 MPs? Might this jitteriness be a non- or much-less- issue for people using AF-On/AF-C?

Thom's most recent article speaks directly to the issue that some bodies might have some issues. But it's not clear if those issues are related to what you're experiencing. Maybe what you're experiences is a fact of life with the new AF-cam module. Maybe you're going to have to adjust your technique. Maybe you have a problem with your particular body. But sooner or later you're going to have to do something besides constantly coming on here and complaining, at least if you want to come to some sort of resolution.

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