Talk about being hoist upon my own petard :( As I strolled to the shops having just posted my last message, it dawned upon me that I'd transformed 1/2,000 into 2/1,000 in my calculation.
If I hadn't been so hasty I would have shown more correctly (I hope this time) that the sensor CoC is 5/8 the maximum acceptable CoC, not 2.5 times more. I think it still proves something, but not as dramatically. It proves that the best sharpness you can get is already 62.5% to the threshold of unsharpness. Recovering that loss of sharpness in post capture processing will sharpen some details that were imaged by the lens as out of focus, I believe. I can't quantify by how much, because I don't remember off the top of my head what CoC that a typical good lens can record on film when critically focused. There is a difference between film and bayer sensor DOF if we believe the photographers who've been droning on endlessly about it for the last few years. I won't be satisfied that there's no difference after all, until somebody posts some samples, but I can't do that at present. My apologies go to John Francis. Consider my hat to be eaten with a large side order of humble pie. regards, Anthony Farr > -----Original Message----- > From: Anthony Farr [mailto:[EMAIL PROTECTED] > Sent: Monday, 18 July 2005 2:45 PM > To: [email protected] > Subject: RE: Theory of Equivalency > > Interesting concept, John. Providing the evidence that proves my claim. > Perhaps you should have done the math yourself before you offered an > opinion. > > The biggest CoC that is perceived as sharp is 1/100in, and the standard > print size for judging it is 8in x 10in (20.3cm x 25.4cm). So it follows > that the biggest CoC at the sensor that will enlarge to 1/100in at 12.69X > enlargement is 0.01in / 12.69, or just under 8/10,000in. > > But you say that the Bayer interpolation increases CoC "on the film" (I > suppose you mean at the sensor) by up to 1/2000in. That's 2.5 times more > than the threshold at which apparently sharp details become apparently > unsharp. > > What point were you trying to make? > > It seems that these numbers prove that NOTHING from an APS Bayer array > sensor should be sharp. IMO these numbers prove that everything up to that > huge CoC requires sharpening in software to bring it back to an acceptable > apparent sharpness. IOW the CoC (or apparent CoC in any case) needs to be > reduced at least 2.5 times to bring an APS digital capture back to the outer > limits of sharpness. > > This means that any out of focus details larger than 8/10,000in and smaller > than 1/2,000in, which SHOULD appear unfocused, will be caught up in the > sharpening. I'll have to leave it to a better mathematical mind than mine > to determine the magnitude of the effect, if anyone even cares. It does > appear to demonstrate that Bayer sensors produce greater DOF than film of an > equal format. > > But please be careful when you accuse someone of operating under a flawed > premise, the claim is just as easily turned back your way. > > regards, > Anthony Farr >
