No, it is not effectively MTF. In fact, lpm is not a transfer function. In fact, being a single point, it does not meet the mathematical definition of a function!
Further, absolute black is available in nature. I did *NOT* claim that absolute black exists or is necessary, but it exists. Stop into an Afghan terrorist cave, have an F-14 seal it up with a missile, and you will "discover" absolute black in the visual spectrum. Further, no mythical absolute white is necessary to measure lpm *NOR* did I claim that it exists. I have no idea where you came up with this nonsense. All that is necessary for the measurement is that the power in the white be significantly higher that the power in the "black". This is why there is a reference to 3 dB or half power in what I said. This is a _relative_ _power_, relative to the peak power in the white. How high is significantly higher? well, that depends on how accurate you want the measurement. Just 15 dB or 5 stops is certainly enough. Measurement of MTF is subject to analogous constraints. Regards, Bob... From: "Raimo Korhonen" <[EMAIL PROTECTED]> > No - I am not wrong - when it is done the way you say, it is effectively MTF. There is no absolute black or white in the nature, or in the world if you will. > Lähettäjä: Bob Blakely <[EMAIL PROTECTED]> > > >No. You are wrong. Lines Per Millimeter is objective. It's often read with > >the human eye, but can be read by instruments. Lines Per Millimeter can also > >be calculated mathematically from the rise from black to white of a single > >edge (or fall from white to black). It is identical to the concept of > >measuring the resolution of a radar (in this case the measure is degrees). > >Generally, the figure is not measured but calculated from the parameters of > >the antenna of which gain is the greatest determining factor. The edge of > >resolution is where (for example) the light (from white to black) falls off > >by 3 dB or half power. It's at this point that two separate objects cannot > >be separated mathematically, let alone visually. For photo surveyors and > >aircraft/spacecraft spies, this is the ONLY measure that counts. FYI, lpm > >for these lenses are not measured by eye but by instruments. Stay tuned for > >an installment on how contrast affects this number. > > > >I do err, but not often and not in areas where I have worked. > > > >Regards, > >Bob... > > > >From: "Raimo Korhonen" <[EMAIL PROTECTED]> > > > > > >> Nope - lpm is measured by human eye and it is quite subjective. I think > >that MTF is the most objective method, it takes into account both contrast > >and sharpness objectively. > >> All the best! > >> Raimo > >> Personal photography homepage at > >http://personal.inet.fi/private/raimo.korhonen > >> > >> Lähettäjä: Bob Blakely <[EMAIL PROTECTED]> > >> > >> >"Sharpness" and resolution are closely tied together, so I will discuss > >them both. > >> > > >> >Resolution is objective and quantifiable. It is a measure of the ability > >to separate two > >> >identical objects as they are brought close together. In photography, > >this is measured in > >> >lines per millimeter where the lines are black the spaces between the > >lines are white. > >> <snip> > >> >Regards, > >> >Bob... > - > This message is from the Pentax-Discuss Mail List. To unsubscribe, > go to http://www.pdml.net and follow the directions. Don't forget to > visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
