Why does focus shift matter?

[pklein]

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So specifically, which lenses are you referring?

Regards,

 

(regarding lenses with no discernable focus shift).

 

Slower lenses don't seem to have as much focus shift. I have not tested this personally, but I bet a 50/2.8 or 50/3.5 Elmar doesn't focus shift as much as a 50/1.4 or even a 50/2.

 

The lenses that are notorious for focus shift even with film are the Noctilux, and f/1.2 and f/1.4 lenses from many manufacturers. Without film's "fudge factor" due to thickness, we just notice it more on a digital camera, especially one with out an anti-aliasing filter.

 

I have no firsthand knowlege of this, but I have a feeling that the new Summarits will have been designed to minimize focus shift.

 

I wonder if the recent Zeiss lenses have less focus shift than the current Leica designs. They are supposedly designed to be digital-ready, and with evenness across the field weighted more heavily than absolute sharpness in the center.

 

Sean mentions that other lenses focus shift. I can tell you that my 50/2 Summicron does. So does my 35/2 Summicron Ver. IV. So does my 50/1.5 VC Nokton. OTOH, Sean notes that the VC 35/1.2 Nokton doesn't have appreciable focus shift. So it's possible to design a superspeed lens today without that problem.

 

In many cases, the focus shift issue doesn't seem to matter photographically at reasonable print sizes. But it bugs the hell out of people when they pixel peep at 1:1. And sometimes it is a deal-breaker. You have to understand the degree to which it matters and act accordingly.

 

Know thy lenses.

 

--Peter

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[sean_reid]

Keep in mind though that even if you use an SLR, you are still focussing with the lens wide open. My Nikon 85mm f1.4 is a fine lens but it exhibits mild focus shift at the working aperture in just the same way that the lenses we talk about here do.

 

That's true with the caveat that with most SLRs one can manually stop down the lens and then refocus. But these focus differences can be so small that it would likely be difficult to actually see them on a ground glass at, say, F/4.