Nikon AF-S 85mm f/1.4 lens not so hot.

Started May 22, 2013 | Discussions thread
MiraShootsNikon
Contributing MemberPosts: 590
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Re: You have a great copy.
In reply to ken6217, May 23, 2013

ken6217 wrote:

MiraShootsNikon wrote:

ken6217 wrote:

Cytokine wrote:

Firstly at 4 feet and f1.4 the depth of field (FX) is 5/8ths of an inch 15mm in metric. NOt for the inexperienced. Which is why pros love this lens and amateurs are moved to tears.

John

I understand that. I actually went to a DOF calculator after I took the images and saw how SHALLOW the DOF is at about the distance you are saying. With that said though, That shouldn't account for me focusing on the eye and the is is not sharp. At 4.5 it is very sharp though.

Maybe I got a bad copy.

Ken

(1) Maybe you need to use Autofocus Fine Tuning.

(2) Maybe you need to try the contrast-detect system in Live View to nail such shallow DoF attempts.

(3) Maybe you need to stop focus-recomposing.

(4) Maybe you're using AF-S and pausing for a split second, breathing, or doing anything else to move the camera in the split second between focus lock and shutter hit.  Maybe your subject is moving slightly, accidentally, too.  It's not difficult to accidentally move out of a 5/8 inch depth-of-field in the delay between AF-S focus lock and firing the shutter.  (Using AF-C with no lock delay / focus priority firing can solve this problem.)

The list of possible reasons why you didn't get a "bad copy" go on and on and on and on . . . .

mira

You could be right, or maybe I got a bad copy.

It's pretty hard to EFF up 1/2000 of a second. And why is it clear at other aperatures?

Ken

Dude, are you joking?  

Look, I don't mean this in a snotty way, but if you're seriously asking why it's "clear at other apertures," then you bought a lens you aren't at all ready for.

But I'll answer: it's "clear at other apertures" because you have more depth of field and you therefore don't need to be as precise with your focusing.   If your depth of field is 5 inches, the camera can pick a focal plane anywhere within the five inches and your shot will look sharp.   If your depth of field is 5/8 inch, the camera--and your technique--has less room for error.

Beyond a certain point, it doesn't matter how fast your shutter speed is.  It matters whether your camera and lens are actually achieving an accurate focus in the first place, and whether you're using the proper technique that'll even allow an accurate focus to happen.  It's true that a very slow shutter speed might cause camera shake or subject motion to blur your photographs, but you're talking like that's the only issue that might cause what you're seeing.

There are other things you need to do to help your camera achieve precise focus.

Here's the list, again:

(1) Are you using AF Fine Tune?  You need to be.  It's not a joke.  There's almost no way you can hit an accurate focus at f/1.4 without fine tuning, for many, many reasons.

(2) Are you trying Contrast Detect (Live View)?  You may need to.  (It is, by the nature of the technology, more precise than through-the-viewfinder phase detect, in case you didn't realize it.)

(3) Are you recomposing after AF-S Focus lock?  If so, there's no way you're going to achieve an accurate focus at f/1.4.  Your recompose movement will almost always accidentally pull the camera  out of the focal plane.

(4) Have you tried AF-C with no lock delay and focus priority firing?   You may need to.  Regardless of your shutter speed, if you're using AF-S, there's going to be a delay much longer than 1/2000 of a second between the time the camera gives you a lock and you fire the shutter.  In that time, you might move.  Your subject might move.  With 5/8 inch at stake, you don't have any room for that.  Therefore, if you use an AF-C mode (again, with no lock delay and with focus priority) the camera will be able to continue evaluating focus to the very moment the shutter actually fires.

Or just send it back, get another "bad copy" and conclude the lens isn't very sharp.  Whatever floats your boat.

mira

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