D800 focus with 1.4 prime lenses is very variable and inaccurate

Started Jan 20, 2013 | Discussions thread
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primeshooter
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D800 focus with 1.4 prime lenses is very variable and inaccurate
Jan 20, 2013

Okay, so many have read my previous thread on my experience with this, I have had alot of pm's about this issue, of people who share my experience.

To re-iterate the problem, the D800 has poor AF accuracy when shooting with a 24-85mm focal length and wide open fast (f/1.4) primes at moderate to far distances, with low contrast subjects. I've found G lenses MAY be a little better but in all honesty D and G lenses have this problem. The camera tends to focus behind or in front of the intended point. AF fine tune is useless because up closer it focuses bang on. Sometimes it grabs correct focus at distance too, but the hit rate is very low.

The settings are AF-S, single, centre point or centre cluster, no area modes, no auto mode no dynamic area, just pure single servo and one focus box.

Now, take my example. For some weird reason this is saying this is a 50mm 1.4D lens. (It's the 1.4G lens, must be a dpreview fault reading the file). Please click for the original versions then +. Focus box was squarely on the child's face, perfectly over his face. But the camera as you can see, has clearly front focused. Infact so much so that the sharpest focus plane is on the man's right arm sleeve of the fleece. I took about 10 shots of this and I got half of them in focus and half like this. The trouble is, whilst his face isn't the highest contrast ever (in high contrast the camera has no problem whatsoever) it should be able to pick this up as the intended focal plane. Trying to focus on something the exact same distance isn't workable, but at this distance at f/1.4 it's noticeable that the child's face is not in focus. This is by far not the worst example I know, and I tried without the hat on the child, with the hat on the child, nothing helps really. I have a whole catalogue of photo's that have this problem now. In low light it's even worse and the hit rate lower. PDAF is terrible in this situation, face's just don't have enough contrast for the D800 unless there is a really contrasty light hitting the subject's face or they are at very close distance to you when shooting. I have extensively tested LV AF. Every time it nails it (as expected) and it can deal with distance and lower contrast as I can zoom in and define edges. But it's too slow, and I shouldn't have to use it on shots like these. If anyone wants to see the full size 36MP shot emailed to them to see how bad it is without dpreview's compression algos and resizing, drop me a pm, and I'll happily send it.



Nikon D800
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