Originally posted by emalvick And for those that want to argue that the DOF represents some plane, it would be more appropriate to argue that the DOF represents the distance between two planes. The two planes being the ones that one could argue separate the area that acceptably in focus from the out of focus areas in front of or behind that area. Of course the location of those planes is again dependent on what the word acceptable means to the individual. Heck, if I take my glasses off, I question whether that acceptable area even exists.
Originally posted by osv defining it as being two delineated planes is essentially the same argument that i posed earlier, when i said that perfect focus can be measured; i posted a 100% crop pic to back that up.
These are different things;
emalvick is talking about DOF {which is "acceptable focus" - basically what we see when viewing the image from a distance which allows us to see the whole thing at once} and you're talking about "perfect focus".
Part of the issue here is technology. If I were to post a scan of a slide I took in 1992, you would rightfully comment on its "lack of sharpness". I had an eye-opening experience when I mounted the Pentax-A 50mm f/1.7 kit-lens {kitted with the Super Program I bought in 1984} on my K-30; the pictures were much sharper than I was getting when I retired that camera + lens in 1995. The difference was
not 20 years of rest for the lens; the difference
is that the K-30 provides much more sharpness than Kodachrome 25 ever did. The same thing is true of today's equipment; no matter how wonderful it may
seem today, it provides only a hint of what is actually out there; that is, true "perfect focus" exists physically only at the molecules located on the plane of focus, but current equipment shows a noticeable difference only when you get some distance away from there. That distance is embedded in our definition of DOF. I don't expect to be around 30 years from now, but I expect that this kind of progress will continue, and the difference between equipment available in 2046 and what we have today could be just as dramatic as the difference between today and 1986. In 2046 any grandchildren {or great grandchildren} in my line might laugh at our best efforts today, and most likely that equipment will show differences {at the pixel-peeking level} earlier as they get away from the plane of focus, but regardless of when those differences show, the simple scientific fact is that the plane of focus is the only place with "perfect focus", regardless of when the differences show up using our equipment.
Last edited by reh321; 04-21-2016 at 07:53 AM.
Reason: arithmetic mistake in originally figuring age of "A" lens