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

Started May 22, 2013 | Discussions thread
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The Fashionable "Bad Copy."
In reply to ken6217, May 23, 2013

ken6217 wrote:

Don't beat him up. I just received my 1.4g today. This is my first prime in like 25 years. I was about to post and ask why I cannot get a clear image at 1.4 on my camera and then I saw this thread.

I am not a pro, but I cant understand why I can't get a clear image at 1.4 on my D800E? At 1/2000 it certainly isn't camera shake. I'm just taking a picture of my son.

I am hugely disappointed. It could be operator error but I don't see how it could be. I take the same picture at 2.8 on my 24-70 and it is crystal clear.

Ken

Ken, it's very clearly "operator error."  Your statement, here, is longhand for "I don't know all the factors at play in getting sharp focus."

It has become fashionable around here to talk about "good copies" and "bad copies" of various lenses like they're vintages of wine.  It's lame.  For your own sanity, I recommend saving the "bad copy" cry for an occasion in which you've actually covered all the bases.  Or at least a few more of them.

Because you write as though you think your camera should always achieve a perfectly accurate focus and slow-shutter camera shake is the only factor that might blur your photographs. Cue the sad trombone on that.

Consider:

  • Fast lenses with spherical elements project more than one focal plane when shot wide open.   Look up "spherical aberration" on wikipedia for an interesting illustration.   Since there isn't a single sharp focal plane to pick, your poor D800E will have a hard, hard time nailing the perfect "one" you have in mind.
  • When using through-the-viewfinder "phase detect" autofocus, Nikon cameras evaluate the scene with an f/5.6 pupil.   In other words, if you shoot wide open, the camera's autofocus sensors can't really see how shallow the depth of field actually is, and so the camera is more or less taking a guess at where, within an f/5.6 depth of field, the f/1.4 focal plane you want actually is.   (The camera sees 4 inches of sharp depth, and guesses where the actual half an inch of sharp focus is within that 4 inches.)  It's a calculated, educated guess based on the lens design and a number of other factors, but still a guess.

Want to know more?  Start here: http://www.dpreview.com/forums/post/50045281

So, while your quick shutter speed is a good start, you also need to help the camera out in a number of other ways.  Such as:

  • No AF-S Focus Recompose
  • AF Fine Tuning
  • Or: Live View (it uses a different, more accurate system to evaluate focus)
  • Or: AF-C, taking care to set the camera's evaluative delay to zero and making sure it snaps with focus-priority, not speed priority.

I think some other folks in this thread have told you the same, so let me add a +20 to all of those comments.  They're not leading you astray or trying to make a mountain out of a molehill.  Shooting a fast prime wide open is different than shooting an f/2.8 zoom, and your statement, above says in a very obvious way, "I didn't know that!"

M.

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