Focusshift???????

Started Jul 20, 2012 | Discussions thread
davexl
Senior MemberPosts: 1,058Gear list
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In reply to Leonard Shepherd, Jul 20, 2012

Do you own a D800 and the 85mm f1.4G, or the 14-24mm?

If you do it is worth your time to learn it, if you like shallow depth of field.

The 85 1.4G when focused at a few meters, will shift focus backwards so that any shot taken between f2 and f5.6 will be just unsharp at the focus point. At f5.6 onwards, the rapidly expanding depth of field regains the focus point. But unless you compensate your eyelash will be soft.

In numbers:
Focus at 200 centimetres at f1.4. Depth of focus is 198.5 to 201.7cm.
At F2.8, sharp focus is between 200.3 and 206 cm. Oops.
At f5.6 sharp focus is between 199 and 211cm. Just ok.
At f8 depth of field is between 196 to 214cm. No problems.

The 14-24 is one very odd lens. Focus at f2.8 at your peril.

Of course, this is most apparent when printing large. Shoot on 12MP and you might never notice.

Leonard Shepherd wrote:

ranamo wrote:

Can someone explain to me what this focusshift is, and why it's a bad thing?

Focus shift is if a lens focuses at slightly different distances at different lens apertures.

As manual and auto focus is usually accomplished with the lens wide open if a say an f2.8 lens with focus shift is used at f11 critical focus may move slightly.

Focus shift ceased to be a significant problem by about the 1950's as new lens technology became widely available.

Some at dpreview imply focus shift with some current lenses can be enormous - I have never found this to be so with the any of the 26 Nikon lenses I own used wide open and f8 - or f11 if an f5.6 lens..

When focus shift is small after stopping down it tends to masked by the increase in depth of field at the smaller aperture.

Perhaps it is like the dpreview D800 LAF debate. A small number of posters claim D800 LAF is a big issue - but 53 images I looked at at dpreview used AF targets where Nikon say Please note that the camera may believe focus has been acquired - when it has not. I have yet to see an example using a subject good for testing a single direction reading outer AF point.

Maybe there is a Nikon lens I do not own with a significant focus shift issue. If there is do not buy it

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Leonard Shepherd

Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.

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Things I have clicked with: Agfa 110, Minolta X-300, X700, Nikon F3, F4, Hassleblad 500C/M, 4x5", Sony F717, D70, D200, Canon 1Ds, II, D2x, D3, Canon 5D-II, D800E

 davexl's gear list:davexl's gear list
Nikon D800E Nikon D810 Nikon AF-S Nikkor 14-24mm f/2.8G ED Nikon AF-S Nikkor 24-70mm f/2.8G ED Nikon AF-S Nikkor 85mm f/1.4G +4 more
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