Originally Posted by
Marco Gilardetti
Dear Bob, I appreciate your experience at Rodenstock USA, as well as your commitment on this forum, believe me. However, the law of physics cannot be overridden and there is no way that while blocking some light with a metal sheet the overall light passing through would be the same. This is, simply put, plain impossible. Should anyone be able to do that, he would win a Nobel prize instantly.
There is also no way that a spheric lens may have two distinct focal lengths. It will have *infinite* focal lengths from center to periphery, each differing infinitesimally by all others within a continuum range. It also cannot have more depth of field than any other doublet of the same type, quite obviously, and behaves just as any other doublet of the same type, obviously again.
The so-called "increased depth of field" affirmed in Rodenstock's documents is due to the fact that the perforated discs intercept the rays at two different radiuses; those will form approximately two (more or less) distinct images corresponding to approximately two focal lenghts (however, it has to be noted once again that the focal lenghts involved are still infinite and continuum around two ranges). This is why details that are not on the same plane may appear approximately in focus on the negative. As a side note, this interesting effect is achieved by blocking off part of the light, at the expense of a decreased f: number when the discs are in place. As always happens in physics, you loose some, you gain some (if it wasn't so, Nobel prize etc.).
By omitting the use of the discs, the photographer gives up this feature and works with *all* the (inifinite) focal lengths set. Not only the diffusion effect will not be quenched, but it actually gets more prominent. The character of the image will of course be different - not necessarily better, not necessarily worse - the Imagon just turns into a different tool.
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