Archived posting to the Leica Users Group, 2004/01/09
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]- ----- Original Message ----- From: "Seth Rosner" <sethrosner@direcway.com> To: <leica-users@mejac.palo-alto.ca.us> Sent: Friday, January 09, 2004 13:53 Subject: Re: [Leica] DR Summicron MTF (was: For your information) > To amplify what I wrote a little while ago: > > > Also remember that "sharpness" is not a objective, quantifiable value as > are > > contrast and resolution. > > Contrast is objective and scientifically quantifiable. As to resolution, one > has to qualify. Unlike contrast, the resolution of a lens does not establish > itself scientifically and mechanically and then transfer to a computer for > print-out. Whether a resolution value is obtained by photographing a wall > chart of smaller and smaller lines or by peering through the ocular of the > EROS machine at smaller and smaller lines projected through the lens (which > is what we did at Optikos), the determined value depends upon what the > observing human eye sees - or thinks it sees - when looking through a loupe > at the negative or at the projected image through the EROS ocular. What one > sees is to a certain extent subjective because the acuity of the human eye > differs from one human to the next. And subjectively, if one wants to think > that one can see line separation at a particular set of line fineness that > equals 250 lp/mm, perhaps one's brain will say: yes I see the separate > lines. Erwin has pointed this out. I did not see it so clearly until this > experience looking through the ocular at Optikos. Which is why, when we were > determining resolution, Roy Youman and I each wrote down our observations at > each f/stop before we knew what the other had "seen." And we then took the > lower resolution value. In this case the resolution recorded was subjective because the eye was being used as a detector. In principle, one need not restrict MTF measurements to 40LPPM max. If data is taken at higher lppm across the field, the resolution can be defined at a specified MTF value, say 5%. This turns it into an objective measurement, but as you can imagine it will be even more labour intensive. > > Who has time for this stuff anyway? Not sure how to respond to this one. I assume, since you organised the tests and reported them here, that you do. Good stuff. I look forward to your article. Do print the curves for all lenses. Regards, Akhil - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html