Focus Problem 85/1.8

[chrisk]

i've been missing quite a few shots with the 85/1.8 due to misfocus. i had thought it was user error but the latest batch i did i had a closer look and almost all shots are not focussing correctly. the confusing part is that some shots appear to be focussed fine, but others are all over the place.

this shot below is evidence of it. its a screenshot from NX which shows the active focus point and its clear it has not focussed anywhere near that. shot @ f3.2 1/400s, iso200, single point AF, single shot drive mode.

can anyone shed any light on this ? why is it an intermittent problem ? that doesnt make any sense to me at all. i'm not having this issue with any other lens but it repeatedley comes up with the 85/1.8. i have done the focus test chart thing and according to that test it looks fine. if you notice in the shot the focus point looks to be behind aswell as in fornt of the red indicator...HUH ??? ie: his right eye and front corner of his jacket look in focus and the middle is out of focus. is that even possible ? lol

what gives ???

[andy]

Was your 'subject' moving as they tend to do? This could explain a lot of it.

As for the focus plane - it looks to me like it travels straight through the left eye, mouth, onto the jacket. I'm guessing you were angled down for this shot?

That's all i've got...

[PiroStitch]

did you have it on continuous focus? if not then the subject moving could explain the issue.

[wendellt]

the lens may need to be calibrated to yoru body but this presentsother problems

because if the lens is recalibrated to the body other lenses will off

the focus plane on 1.8 is so shalow you usually get missed focus issues

if your technique is sound the only thing you can do i focus in maual mode with attention to compensating for the misfocus

lenses also misfocus because off low light and the fact that the motor drive(AFD)) nature of the lens isn't that fast so if the subject moves the focus is slightly off because the lens hasn't had time to re-focus

otherwise your too close to the subject so the minimum focus distance is hinderign the focus

ive had my 85f1.4 and it does this quite alot i just learned to live with it till i can get a 2nd dedicated body which will be calibrated to that lens

[gstark]

Could we please have a lok at the exif data?

I'm thinking that this is subject movement, rather than OOF. The area shown as being in focus looks, to me, to be in a very close olane with the corner of the jacket. The other areas cited seem to be somewhat sharp, but not as sharp as the jacket.

Now, if we look at the hair on the rh side of the image, this appears to have been shot on a somewhat windy day. Extrapolate that to include the hair on the subject's forehead also being blown around, add a dash of shutter speed slower than say 1/160, and we might have a potential explanation for this one image.

Might ...

And it goes nowhere near explaining the other images where you're seeing this issue.

So, EXIF, please, and maybe a couple more suspect images.

[chrisk]

thanks for the responses. Gary, exif is in OP, f3.2 1/400s, iso200.

unfortuantley i've deleted all other examples except the ones from this particualr set. here is another example of misfocus.



then the 2 after that it focussed fine.





same conditions, same aperture, relatively the same shutter speed, (Ap so there is some slight variances in SS but nothing under 1/400s), CW metering, single shot AF.

good point about aiming down, i didnt think of that. not sure i was. i think this is standing front on but i cant remember. the 85 has a pretty crap MFD so i doubt i would have been looking down on him at that distance. but food for thought anyway.

its driving me mental and its a pain cos its unreliable. i shoot at large apertures all the time with all my other lens' and i dont have this issue. i used the 105VR for another set in similar conditions and they were all perfect. btw: the AF point used is always the same one, (centre), it just looks like a different AF point cos of the crops.

[chrisk]

i returned it to D-D today, we will see what their service is like for a lens repair.

[ATJ]

single shot AF.

There's your problem. Unless you are shooting a static subject with the camera on a tripod, you should be using AF-C. With AF-S, once focus is attained the lens won't focus again. If there is any movement (of the camera or the subject) between when focus was acquired and the shot being taken, the shot will be out of focus despite what the focus indicator says.

Here are a couple of examples from using AF-S.

The first one there was no movement between focus and taking the shot:


The second one I purposely moved the camera after acquiring focus:

[chrisk]

interesting. you raise a good point.

i've not changed my shooting habits from lens to lens though. i always shoot in af-s for this type of shot ad dont have this issue with other lens'. i dunno, something doesnt sit right with this lens. maybe you're right and this is what the problem is. oh well, it'll get assessed and we'll see what they come back with. if nothing else, and they come back and say there's nothing wrong with it then it gives me some peace of mind that it is user error and its been checked out.

[ATJ]

Do you shoot with your other lenses at f/3.2? That wide open DOF will be much smaller and any OOF areas will be more noticeable.

[chrisk]

yepp, there or thereabouts.

[Yi-P]

With the 85/1.4 I have here, I do have this problem sometimes, it is not because it's mis-focusing, but the focus plane is not on the target you trying to photograph. The DOF is so shallow that a single mm movement can mean out of focus. Specially photographing things at an angle.

This problem is more pronounced when you are used to pre-focus, recompose and shoot.

[chrisk]

big wrap for Sam @ D-D photographics. seems no end of positive feedback for these guys.

i picked up my lens this morning and the report from the repair was severe "backfocussing" which they realigned or whatever the hell it is that they do. less than a 4 week turnaround time and it works a treat so far !

good to know that these guys are more than just a cheap seller, their after sales/ warranty service is top notch.