DanielMitchell@xxxxxxxxxxxxx writes:
<< why isn't the 16mm f0.6? Is it some sort of
coincidence that 50mm happens to match up with the least amount of glass and
that's why it's the "standard" lens?
>>
An additional confounding issue here is the fact that an SLR needs to have
retrofocus lenses when the focal length gets short enough that the lens would
sit where the mirror is with a non-retro design. So RF cameras have quite
small wide angle lenses compared to an SLR. The Zeiss Hologon camera lens
(15mm ) is much smaller than say the equivalent rectilinear Nikon or Sigma
15mm lens for an SLR. When the Hologon first came out it was thought that a
rectilinear SLR lens of that focal length could not be made.
As far as fast glass under F1.0 is concerned, microscopes objectives often
achieve numbers well under 1.0 ( as low as F 0.5? I think) when they use oil
immersion objectives. The immersion objective gives a much larger relative
refractive index between the glass and the oil.
So if we could invent some new glass with much higher refractive index we
might get faster lenses?
For monochromatic light where the lens does not suffer chromatic abberation,
going to a faster lens improves resolution greatly since the lens can then be
difffraction limited even wide open. This is exactly what is done in the
semiconductor industry with mainly Nikon process lenses for
photo-lithographic production of masks for semiconductor chips. These lenses
are ~ F0.8 I believe, and used to be corrected at two wavelengths. One
visible for allowing checking of focussing manually and another in the UV for
actual exposure to minimize diffraction.
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
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