RustyBug
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 p.15 #15 · Voigtlander 28mm f/2 APO-Lanthar Review | |
The premise of taking an APO that has gone to great levels of precision in order to get the wavelengths to converge properly ... and then forcing it through an optical path (wrong stack) that it was never designed for ... is a bit like taking a Monte Blanc and trying to write on sandpaper with it.
Sure, you'll be using a Monte Blanc, but you're not gonna get the same experience with it as if you were writing on a piece of fine paper.
At the center, where the light rays are most perpendicular to the stack, the refraction variance will not be significantly effected. But, the greater you change the angle of incidence (from perpendicular), the greater the angle of refraction will continue to "mis-align" the wavelengths, thus defeating the APO's precision. The wider you go (and thus, farther from perpendicular), the tougher it gets.
If you're looking at adapting the APO and using its Apochromatic properties in Zone A, allowing for Zone B / C to be non-Apochromatic, due to the AI=AR as it passes through the stack at wider angles ... then that's where things will land. If this were a 90mm APO being adapted, then the AI=AR being more telecentric / collimated (i.e. closer to perpendicular) might not be as greatly efffect. But, with a WA ... I can't see any reason to expect that the Apochromatic properties would be retained by adapting to the wrong size stack, as the optical path (and greater angles of AI=AR) moves from Zone A > Zone B > Zone C.
I mean, the APO is trying to align wavelengths of light in terms on nanometer precision, and we're talking about forcing the light path through a stack that is roughly 1mm thicker (nm 10^-9 vs. mm 10^-3) ... throwing off the alignment, predicated on the AI=AR passing through the greater distance, as the light is diverging vs. converging.
Whatever amount of wavelength misalignment is occurring through an M stack, due to its AI=AR ... if the adapted stack thickness is greater than that of the M, the misalignment of wavelength is going to be proportionally greater (basic trigonometry).
This principle of Leica using a thinner stack, is key to reducing the divergence of the light. The impact of moving away from that thickness, is going to effect the projection. This is true in general ... but, as the precision of the APO is more refined, then need to retain it, is then a greater "mismatch" ... i.e. exceed the precision of the APO's wavelength alignment.
Except for the benefit to Zone A, why bother with the extra size of the APO, if the thicker stack is gonna mitigate the APO precision in Zone B / C on an adapted body? If you're good with the Zone A precision of Apochromatic, foregoing Zone B / C ... then, sure why not. Otherwise, why?
Think about it. 
Edited on Aug 04, 2025 at 06:58 AM · View previous versions
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