Front focus

[bwud]

My A7R II seems very susceptible to front focus when using eyeAF, which I wouldn't expect given on-sensor AF. Is there a way to adjust similar to MFA on SLR cameras?

 

Or is it perhaps using contrast for the final determination of focus, and getting hung up on eyelashes?

[bwud]

Sorry for the quality (shot of EVF zoomed to AF area), but here are a couple examples. Using EyeAF, I find it hits lashes more often than not.

 

http://i.imgur.com/jcHHcT1.jpg

 

http://i.imgur.com/p8piG2I.jpg

[bwud]

Here are 1:1 crops.

 

My hit rate seems much higher on other lenses than this one (batis 85), hence the question about adjustments.

 

[Guest Peter Kelly]

Clearly, this is not ideal, but it's hard to work out exactly where the problem may be.

 

First of all, what f number are you using? If, as I imagine, you're shooting wide open then it might be a motion issue, rather than focus point.

I don't mean that as in motion blur, or even suggesting your technique is flawed, but the 'hit rate' is always going to be low when using the shallowest of DoF, simply because both you and the subject are almost certainly swaying slightly. This might be even more likely if the Batis is not particularly fast at focussing (I don't have experience of this as I still can't get one...grrrr!).

 

That said, you would imagine to get an equal number of back focussed pictures, so careful analysis of all the shots taken would be needed to absolutely verify.

 

If the situation is exactly as you believe (could easily be) then it could be down to what you suspect, although it doesn't have to be limited to CDAF; that could just as easily be PDAF if that is the only part that gives a suitable image for 'lock-on'. I suspect the only way to verify that would be to try different subjects with different colouring; maybe even get some young lady to wear various types of eye make-up and see what effect it has.

 

Even so, before you do any of that, you will need to thoroughly check the lens as to its overall sharpness. What you may be seeing here could possibly be that the lashes are no more sharp than the rest of the eye, but merely appear so because of their natural contrast and shape! I've often had times where I think that the focus is slightly off when it comes to looking at the face, yet when you analyse other elements such as clothing to determine where the focal plane lies, it isn't wrong at all. Faces and skin merely appear softer, compared to something like fabric. I'm sure there is someone who could explain such an optical effect.

 

The only other possibility I can think of relates to how your continuous focussing is operating. Try listening to check if it is still moving. Ultimately, if your camera is not performing as you'd like (and it doesn't look ideal) then it might be worth getting it checked out, as there could be an issue with it.

[bwud]

Thanks for your thoughts.

 

Yes these are wide open and near MFD so of course there is little margin for error. And yes, my son was moving. I was shooting AF-C with EyeAF; it is possible he shifted slightly back between the time it focused and the time the shutter closed. But when it's off, it always looks like front focus, and like you said one would expect 50/50 front and back.

 

 

When it's on, it's very good. I'll pull out an example shortly.

[bwud]

Here's a good hit.

 

I suspect maybe it's a combination of technique and focus speed. I can't expect miracles, especially near MFD wide open.

 

[Guest Peter Kelly]

You're right about minimal error! +/- about 6mm at that distance, so you have little room to play with.

 

The one other thought I had relates to you and shutter lag. This is not a criticism at all, because we probably all do it to an extent, but I wonder if you have a slight unconscious movement after pressing the shutter?

If you do, almost some form of relaxation after the initial concentration, then if there is a little shutter lag you will be in a slightly different position when the shutter actually releases.

 

I know when I'm waiting for, or looking to optimise, a particular shot I can get quite tense simply holding steady for the right moment. It makes a shoot a tiring affair!

If you have an instinctive tendency to react once you've pressed the shutter than it may be always in the same direction, which most likely would be backwards and give the results you are seeing.

 

I have absolutely no idea how you'd test my theory, other than making a huge force of will to maintain a position long after pressing the shutter, but our bodies have a way of doing what they want irrespective of our best efforts!

Perhaps you could get an observer to watch, or video, from the side and carefully compare position with shutter release noise?

 

It still doesn't explain why other lenses are better, unless there is some strange combination at work here (shutter lag, particular AF speed of the lens, your movement, focal length?), but my head is beginning to ache...

[Golem]

Clearly, this is not ideal, but it's hard to work out

exactly where the problem may be.

 

First of all, what f number are you using? If, as I imagine,

you're shooting wide open then it might be a motion issue,

rather than focus point.

I don't mean that as in motion blur, or even suggesting your

technique is flawed, but the 'hit rate' is always going to

be low when using the shallowest of DoF,

My thoughts also. Peeps are using way too shallow DOF,

clearly under the influence of the bokeh cult. There seems

to be a belief that wide apertures relieve you of the tedious

responsibility of considering the background, while state-of-

the-art AF will insure focus. Seems you have encountered

one of those live-and-learn moments. So live, and learn.

 

Rather than pick this all apart in another of my infamous

loooong posts, I'll just say that it's verrrry fuckdup.

 

I could say more .......

 

Maybe just a tiny bit more: If you don't like the way the

eye focus does things, turn the damnt thing off. If you

can't get what you expect from AF, practice more on your

manual focus. It's not newkyular physics after all ... You

posted a sample that shows what you want. So, just do it.

Practice isn't about learning HOW to MF. Anyone CAN MF.

Practice is about YOU becoming the accurate unthinking

unblinking rapid focus device. You ARE superior to any

plastic box, but your ability might be dormant. Practice

is about waking it up.

 

Oooooopzez, I wrote another long[ish] post again ....

[bwud]

The one other thought I had relates to you and shutter lag. This is not a criticism at all, because we probably all do it to an extent, but I wonder if you have a slight unconscious movement after pressing the shutter?

If you do, almost some form of relaxation after the initial concentration, then if there is a little shutter lag you will be in a slightly different position when the shutter actually releases.

 

know when I'm waiting for, or looking to optimise, a particular shot I can get quite tense simply holding steady for the right moment. It makes a shoot a tiring affair!

If you have an instinctive tendency to react once you've pressed the shutter than it may be always in the same direction, which most likely would be backwards and give the results you are seeing.

 

Interesting thought. I suppose it's possible, but generally I'm shooting a series of photos, not just one.

 

It still doesn't explain why other lenses are better, unless there is some strange combination at work here (shutter lag, particular AF speed of the lens, your movement, focal length?), but my head is beginning to ache...

 

Haha! I guess I'm really picking nits here. I guess I was just surprised; the camera does a respectable job recognizing eyes, I thought it would be equally good at ignoring things which are often in front of them (lashes)!

My thoughts exactly. Peeps are using waaaay too shallow DOF,

clearly under the influence of the bokeh cult. There seems to

be a belief that wide apertures relieve you of the tedious

responsibility of considering the background, while state-of-

the-art AF will insure focus.

 

Rather than pick this all apart in another of my infamous

loooong posts, I'll just say that it's verrrry fuckdup.

 

I could say more .......

Typically I don't shoot this lens wide open. However, can there be a better way to determine the limits of the AF tech? Besides, if I want a certain look which wide lenses afford, what's wrong with using them as such?

[Guest Peter Kelly]

...generally I'm shooting a series of photos, not just one.

 

 

 

Out of curiosity, how do the series of shots compare? If they follow a pattern then it might be possible to figure out if there is a particular explanation.

 

i.e. If they get progressively more or less blurred then it could be simple movement, yours or your subject. If they are all pretty well identical then it would seem to be a wrong choice by the AF. If they vary randomly then I'd suspect the AF is not absolutely fixed and still adjusting which, I suppose, is what might be expected to an extent.

 

As Golem says, though, such shallow DoF is always very difficult to use, but I certainly think you are doing the right thing by testing the envelope!

[bwud]

This recent series was about half hits (which is impressive considering the challenge), but not long enough to really look for a pattern.

 

I didn't mean I just mash the shutter until the buffer fills. By series I meant I keep AF on and shoot in expressions I like, so there's not really a "got it/relax" moment.

 

It would be interesting to put it in a tripod and do some repeatable tests. Shooting a moving subject is never going to be conclusive, but I could certainly do some stuff with my LensAlign to see if it's really me or the camera/lens.

[Guest Peter Kelly]

I think a 50% hit rate is pretty good for those challenging conditions, but it would be an ineresting exercise to see just how far technique might affect such shooting.

As I say, there are probably involuntary movements we all make under certain conditions, yet don't know we do it. It's the reason top marksman will spend hours perfecting a trigger action, just so they dont pull off target.

 

I remember seeing an 'out-take' once where an advert maker was trying to get a man to say a particular phrase without any movement of his head, but he kept nodding a tiny bit every time. The takes ran to hundreds!

It's just this sort of involuntary motion that might have an effect.

 

If you are concentrating on the expression it may well be that there is a point where your brain subconsciously says, "I've got that shot, now set for the next one" and introduces a little movement that you won't even be aware.

That's all it would take to throw the AF here.

 

Whether you do something similar, or in reality have an excellent technique so that I'm way off the mark, my curiosity is aroused!