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.

I suspect your focus point has shifted. A good technique is to use a single focus point, half depress the shutter release when acquired, recompose (while half depressed) and fully depress the shutter. Try it.

Hi, thanks for the suggestion. I did use single focus point (the center one), and I don't usually recompose, at least not with the problematic photos. That's why it's strange to me that the focus could go behind that much---and with other tests no obvious focus shift was seen.And be the way, I shot handhold only, usually the shutter speed is not bad in those bright environments (200, 500, 1000+).

Allow me to show some sample here: 50% crop taken by windows screenshot tool from viewnx2.It's photoed in sun slight, F4.0, shutter speed was 1/640s, raw, I might have pull the exposure back by a stop for the over exposure with a smaller aperture, single focus point, no recompose. the red frame shows where the focus is (or intended to be). The funny thing is that it seems not reproducible with other subjects.

Steve Bingham wrote:I suspect your focus point has shifted. A good technique is to use a single focus point, half depress the shutter release when acquired, recompose (while half depressed) and fully depress the shutter. Try it.That is the best technique for getting OOF shots of people when using wide apertures...I set focus point and use af-c, this higher increased my keeper rate when I quit using af-s and recompose method. Using what he suggestedallowsthe focus to shift between the time you acquire focus and the shutter is released. It almost insures it.

liwei zhen wrote:Allow me to show some sample here: 50% crop taken by windows screenshot tool from viewnx2.Obviously is back focusing but if if it is inconsistent, might be a camera defect? I've never seen a person's eye causing any of my dSLR's to back focus like this.

Sometimes the camera goofs. Sometimes the lens fails to focus properly. If this is common I would keep testing and maybe return the lens. (Not really a favorite of mine).liwei zhen wrote:Allow me to show some sample here: 50% crop taken by windows screenshot tool from viewnx2.It's photoed in sun slight, F4.0, shutter speed was 1/640s, raw, I might have pull the exposure back by a stop for the over exposure with a smaller aperture, single focus point, no recompose. the red frame shows where the focus is (or intended to be). The funny thing is that it seems not reproducible with other subjects.

Stacey_K wrote:Steve Bingham wrote:I suspect your focus point has shifted. A good technique is to use a single focus point, half depress the shutter release when acquired, recompose (while half depressed) and fully depress the shutter. Try it.That is the best technique for getting OOF shots of people when using wide apertures...I set focus point and use af-c, this higher increased my keeper rate when I quit using af-s and recompose method. Using what he suggestedallowsthe focus to shift between the time you acquire focus and the shutter is released. It almost insures it.Not really Stacey, if your camera is set up correctly. The half depressionkeepsthe camera focused on that original area as you move the camera and DON"T let up on the shutter release.Use AF-Sof course. I have been using this method for many years - D2x, D200, D300, D600, D610, D700, D7000, D800, and D5300. Yeah, between my wife and I we have gone through a lot of Nikons.:) Also worked great with the Kodak SLR/n, and 2 Fuji X cameras.

liwei zhen wrote:Allow me to show some sample here: 50% crop taken by windows screenshot tool from viewnx2.It's photoed in sun slight, F4.0, shutter speed was 1/640s, raw, I might have pull the exposure back by a stop for the over exposure with a smaller aperture, single focus point, no recompose. the red frame shows where the focus is (or intended to be). The funny thing is that it seems not reproducible with other subjects.I feel your pain ..... trying to get that spot on focus with that lens is a bit problematic for me as well.Just a thought about your example photo ...... even if the focus point shown by the red box represents a cross-type point, the majority of the box is featureless and likely not providing much for the sensor to actually focus on.  The eye is all above the horizontal mid-line and mostly to the left of the vertical mid-line.  So maybe try placing the entire eye-socket in the middle of the focus sensor and see if that makes a difference?

Thanks, HX100V. You are probably right, I missed the point of how the DSLR focus system works. It is a cross focus point. And actually the refection part in the eye may not be tested in the AF system at all.If the displayed AF point is very accurate (my hand may have shaken slightly between focus lock and full press), there is a good contrasting point on the upper part of the vertical mid line: where the eyeball and eyelid join. I think that's pretty enough for the system to make decision.Actually the decisiveness of the AF is very good even in very low light (and most of the time lock on accurately), so I'm so impressed that it's not confused, but cheated: could it be the lower eyelid? I always find that part of my son watery and shines ^_^.The "detection lines" is good point though, I will check some more pictures and shoot some more to see...

Stacey_K wrote:liwei zhen wrote:Allow me to show some sample here: 50% crop taken by windows screenshot tool from viewnx2.Obviously is back focusing but if if it is inconsistent, might be a camera defect? I've never seen a person's eye causing any of my dSLR's to back focus like this.Hi, thanks. I never googled a case like that too. Good to hear confirmation from some experienced people.Not sure if it's a defect too: it seemingly has a pattern (like stated above), and I have like 5-10 pictures shift like this one. But none in other conditions (like lower light).My lens does have a small and shallow scratch (maybe like 3mm by 1mm) by my son, not too far from the center. But again if it matters (I doubt) it doesn't explain why in most situation the focus is good.

Steve Bingham wrote:Stacey_K wrote:Steve Bingham wrote:I suspect your focus point has shifted. A good technique is to use a single focus point, half depress the shutter release when acquired, recompose (while half depressed) and fully depress the shutter. Try it.That is the best technique for getting OOF shots of people when using wide apertures...I set focus point and use af-c, this higher increased my keeper rate when I quit using af-s and recompose method. Using what he suggestedallowsthe focus to shift between the time you acquire focus and the shutter is released. It almost insures it.Not really Stacey, if your camera is set up correctly. The half depressionkeepsthe camera focused on that original area as you move the camera and DON"T let up on the shutter release.Use AF-Sof course. I have been using this method for many years - D2x, D200, D300, D600, D610, D700, D7000, D800, and D5300. Yeah, between my wife and I we have gone through a lot of Nikons.:) Also worked great with the Kodak SLR/n, and 2 Fuji X cameras.Thanks for the comments. BTW, how did you recompose? I mean did you shift along the focal plane, or did you rotate the camera. I think the rotation may place the subject a bit closer to camera from the plane of focus, if the DOF is shallow (close subject + wide aperture)?Sometimes the camera goofs. Sometimes the lens fails to focus properly. If this is common I would keep testing and maybe return the lens. (Not really a favorite of mine).Yes, will test some more. And we don't have so liberal a policy to return the lens or camera, I can get them fixed or sold second hand, if they are really defective.

liwei zhen wrote:Thanks for the comments. BTW, how did you recompose? I mean did you shift along the focal plane, or did you rotate the camera. I think the rotation may place the subject a bit closer to camera from the plane of focus, if the DOF is shallow (close subject + wide aperture)?You already figured out why this technique doesn't workSeriously try using AF-C if you aren't. The other reason to use AF-C is that as you slightly move the focus point around the eye, you will likely see, at some point, it snaps into focus. Using AF-S, you'll never see this.These focus points and their markings are not always 100% perfect, there are manufacturing tolerances.It could be there is a camera defect or that lens just has issues. My guess is more on technique.

Was your example photo just a picture from your shooting that day or was it a test?I'm just guessing but here's a thought to consider.When people photograph small children like this it's very common to crouch down and lean in to get somewhat close.  The problem with leaning in is that your momentum is going to often have you moving slightly forward and you might not even notice it.  If you move slightly forward in-between focus acquisition and shutter release your focus point will move back the same amount of inches.Think about it this way.  If I go to take this picture and I crouch and lean forward and I half press the shutter button and I'm exactly 40" from the close eye that I want in focus, but the momentum of my leaning forward causes me to move a few inches forward, when I capture the photo the close eye is only 37" away, but my focus is still at 40", which puts the rear eye right in the focus sweet spot.I would try to test this in a fairly controlled situation, paying close attention to your technique.That said, I've always felt my 35mm f1.8 gives me a relatively low keeper rate and I don't know exactly why.

Nexu1 wrote:Was your example photo just a picture from your shooting that day or was it a test?I'm just guessing but here's a thought to consider.When people photograph small children like this it's very common to crouch down and lean in to get somewhat close. The problem with leaning in is that your momentum is going to often have you moving slightly forward and you might not even notice it. If you move slightly forward in-between focus acquisition and shutter release your focus point will move back the same amount of inches.Think about it this way. If I go to take this picture and I crouch and lean forward and I half press the shutter button and I'm exactly 40" from the close eye that I want in focus, but the momentum of my leaning forward causes me to move a few inches forward, when I capture the photo the close eye is only 37" away, but my focus is still at 40", which puts the rear eye right in the focus sweet spot.I would try to test this in a fairly controlled situation, paying close attention to your technique.That said, I've always felt my 35mm f1.8 gives me a relatively low keeper rate and I don't know exactly why.Which is another reason to not use AF-S for hand held shooting like this. If you were using AF-C, the shot would be in focus. I read someone who is very accomplished explain why to not use AF-S and once I started using AF-C for almost everything, I rarely have OOF images anymore.

Stacey_K wrote:Nexu1 wrote:Was your example photo just a picture from your shooting that day or was it a test?I'm just guessing but here's a thought to consider.When people photograph small children like this it's very common to crouch down and lean in to get somewhat close. The problem with leaning in is that your momentum is going to often have you moving slightly forward and you might not even notice it. If you move slightly forward in-between focus acquisition and shutter release your focus point will move back the same amount of inches.Think about it this way. If I go to take this picture and I crouch and lean forward and I half press the shutter button and I'm exactly 40" from the close eye that I want in focus, but the momentum of my leaning forward causes me to move a few inches forward, when I capture the photo the close eye is only 37" away, but my focus is still at 40", which puts the rear eye right in the focus sweet spot.I would try to test this in a fairly controlled situation, paying close attention to your technique.That said, I've always felt my 35mm f1.8 gives me a relatively low keeper rate and I don't know exactly why.Which is another reason to not use AF-S for hand held shooting like this. If you were using AF-C, the shot would be in focus. I read someone who is very accomplished explain why to not use AF-S and once I started using AF-C for almost everything, I rarely have OOF images anymore.Somewhat agree here. Now that I have moved to AF-C (almost exclusively) keeper rate has soared in this and most situations...but that included a move to back-button focus (best of both worlds). When the camera is handheld, or the subject is alive...the focus situation is dynamic so AF-C often has an advantage.That said, an experienced photog, with skill, likely knows all that and has nearly as high a keeper rate with AF-S. You get good with the mode you constantly perfect. I've seen experienced focus recomposers instinctively move in and out with the moves of the subject. They seem to not even realize they are doing it. Like AF-C with their bodyThere simply is no perfect focus mode or best one for every situation. AF-C has it's own issues. It never tells you when it has decided to switch to a different contrast than the originally intended one. It is often better served by a change in AF-Area mode but doesn't tell you that. Pros and Cons...no absolutes

Thanks guys. It turns out it is a back focus in the combo. And sorry that I misled you by saying that tests on other subjects were okay.I tested with a tripod + several toy blocks lined up in a row (45 degrees from the focal plane). AF-S, single focus point, f1.8.The result is that when the camera is 0.5 or 0.6 meter (2 feet) away, there is no obvious back focus. When the distance get to 1 meter (3 feet), the back focus is very much perceivable, it's like 3-4 CM (1+ inch) back from where it should be. When I still double the distance to 2 meters, I think the problem goes even more severe (because the DOF goes thicker, but I still see similar or bigger shift), but not very sure.So I guess you people are all correct to say "no" to the original question of mine, and suggesting the combo to be defective. I marked the first 2 as correct answers, but thanks to all the good suggestions.I guess I will send the combo to Nikon for tweak/repair (likely they won't take them back and refund me), or maybe I just re-sell the camera before they mess with the inside of the body---some people may have a lens that works fine with the body.The AF-C is a good idea too, I played with it + the 3D tracking: the tracking is quite good I think.

Silly me, turns out I can only mark one correct answer, so I re-marked Stacey's post since she said it first. Thanks to you too, Steve.

Stacey_K wrote:Obviously is back focusing but if if it is inconsistent, might be a camera defect? I've never seen a person's eye causing any of my dSLR's to back focus like this.If focus has locked onto the reflection itself the camera to subject distance will be the camera to reflected object distance - same as focussing on a mirror.In fact, eye reflections have long since fascinated me and I seek the opportunities to make such images deliberately. Here's an example, the apparent subject is the eye (of a carrion crow) but the real subject is me and my house reflected in his eye.D70, Sigma 105mmHere is another, a squirrel in my back garden:D70, Nik 300/F4 AFSHowever, I would be surprised if normal portraiture of humans would in practice be affected by eye reflections.David

Steve Bingham wrote:Sometimes the camera goofs. Sometimes the lens fails to focus properly.Sometimes(it seems well over 99% of the time base on posted images)the photographer goofs by expecting AF to work well in circumstances where the camera instructions explain AF may not be accurate.This seems a good example of an equipment owner not realising focus may not be accurate with this type of subject.