D600 Question: focus points too limited? A: Yes

Started Nov 19, 2012 | Discussions thread
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TOF guy MOD Forum Pro • Posts: 13,306
Re: A: AF-S + FVL

wireless wrote:

TOF guy wrote:

amooz wrote:

Focus on her eye, recompose your shot,

And induce misfocusing error which with a fast lens wide opened will be enough to be detrimental to the picture

[...]

Could you explain a bit more why this happens?

There are a number of useful explanations on the subject such as this one .

Does the subject move before reframing?

This is all assuming no other motion (subject and camera) than the "recompose" motion.

I thought once you focused and had AF-lock with shutter button halfway pressed, you'd still focus.

With AFS, on a D800/D800e, once focus is locked it does not change even if the subject starts moving towards the camera. The workaround is to switch to AF-C.

AF-C combined with 51 points / 3D mode allows focus and recompose without any loss of accuracy. In AF-C mode the camera tracks a moving subject, and 3D keep the tabs on the subject by using the color information from the metering chip. The key point here is that the camera can't make the  difference between a subject which moves while the camera doesn't, and a subject which stays in place while the camera moves: in both situations the camera will adjust for the subject-camera distance regardless of who or what is moving. So what you do is select the sensor exactly on top of the subject eye, recompose with shutter half-pressed: you should see the selected sensor change so that the selected sensor is always the one on top of the eye thanks to the 3D mode. When satisfied with the composition fully depress the shutter.

And on that subject, how do you even get tack sharp focus on someone's eye? Even with single point I can't seem to get that focus very often on shallow DOF.

It's hard to provide explanation without knowing a bit more. Here are some suggestions which may or may not be relevant to you: 1) beware of focus and recompose in AFS 2) avoid waiting with shutter half depressed in AFS: that's because you may unintentionally move your body / head a little forward or backward which would compromise focusing accuracy (again in AFS once focus is locked it does not change even if the distance to subject starts changing) 3) When in doubt: double-focus: lock focus, release shutter and re-lock focus: you should sense that the lens does not move 4) use either AFC 3D as explained above (seems counter intuitive but it works) or the new  face priority AFC which is quite good in good light.

My experience is with the D800e. There is a 3D tracking mode on the D600 but its performance may not be as good because the color information from the metering cell is very limited (2,000 points D600 compared to 51,000 D800/D800e/D4). The 3D tracking mode on the D300 (1,000 points) has a bad habit of dropping the subject quite quickly. I suspect that the D600 performance is more alike the D300 than the D800. D600 users will certainly share their experience.

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Thierry

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