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Originally Posted by wparsonsgisnet
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Back to my specific recommendation -- is the infinity mark on the lens still correct? If so, why wouldn't the hyperfocal distance be correct when getting inside the corresponding aperture mark? That is, if I'm shooting at f8 and I set the infinity mark to 5.6, won't I have everything in focus from infinity to somewhere about the distance on the lens at the other 5.6 mark?
Per Sean's prescription, I will test this hypothesis. It's supposed to rain this weekend, anyway.
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Bill, no matter what, the lens will have its plane of best focus where it is set, as long as sensor-lens alignment is correct. And, disregarding some of the more peculiar opinions expressed in this forum, I do think Leica does get this right. So infinity is infinity, i.e. somewhere beyond the Kuiper Belt …
Now if you set your aperture to 8 and the infinity mark opposite the far f:4 mark on the d.o.f. scale, then you will have everything in focus down to the distance opposite the near f:4 mark – that's what 'hyperfocal' means – as long as you do not insist on an even smaller circle of confusion than .015 mm. But as I have written before, the practical criterion is what it takes to produce a visually sharp A4 or 8x10" or 18x24 cm print. This is all you can take in at 30 cm. Anything larger will be viewed at a correspondingly larger distance, which will permit a larger print c.o.c. A 16x20" for instance cannot be comfortably viewed closer than 60 cm so the permissible print c.o.c. will be 1/5th of a mm!
There are of course cranks who will procure a two by three foot enlargement and use a 10x magnifier to search for the unsharpness or grain or whatever that their hearts crave. It goes without saying that they will always find it. But these people are not into photography but into fault-finding, and they could just as well have searched for their faults in musical recordings, or pole vaulting, or whatever.
Another reservation: An optical system which exhibits really low definition all over, will of course lack a discernible depth of field. The prime example is the pinhole camera. Here, the distinction between sharp and unsharp is meaningless. Even in a glass lens, low resolution and contrast may mean that the transition from (not very) sharp to unsharp seems smoother and maybe more pleasant than in a crisper lens, where it will be seen as more abrupt. This may bear on Sean's argument. Soft focus lenses or 'soft filters' (diffusers) may subjectively seem to create more depth of field, for this reason. But d.o.f. is a physical quantity that can be measured and computed, and the arguments above hold, as long as you can at all discern where the plane of best focus lies!
The old man from the Age of the Rodenstock Imagon.