Could the refection in subject's eye affect AF (D5300)?

Started Mar 26, 2014 | Questions thread
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liwei zhen
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Could the refection in subject's eye affect AF (D5300)?
Mar 26, 2014

Hi, first time poster here. Recently I got a D5300 + 35mm f1.8g DX, it's a nice combo and all. But occasionally I see quite some degree of focus shift when AF on my kid's eye.

I took some not-so-strict tests with a row of batteries or similar thing, cannot really see focus shift. While the focus shift happens under these criteria:

1. usually it's quite bright scenario.

2. AF-S with center focus point, and put it over the nearer eye of the kid.

3. Aperture can be 1.8 to 4.5, sometimes even 5.6.

4. the distance is about 1 or 2 meters (several feet).

5. the eye on which I focused was open rather wide.

Then sometimes I see the focus shifted "a lot" behind, usually the farther eye will be in focus.

I considered this for quite some time and looked up on web quite much, but found no similar situation. Then I see that most of the "back focus" pictures have quite some reflected subject in the intended eye: the shadow of my self or some other big object, so I wonder could it be the refection in the eye that shifted my focus?

I mean the reflection is like a reflection in a mirror, just the eye is with a outwardly curved surface, and with low contrast reflection. Then could it be the reflection that make the "back focus", like when focusing a subject in a mirror, the focus fall in the mirrored subject but not the mirror itself.

Tried with some dolls with plastic eyes, cannot reproduce it---the eyes are not that smooth, and the scenario could be a little different.

Look about on the web to see if there was any theory about this, but never found on answer. Any comments? Thanks a lot.

Nikon D5300
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