At 03:26 12/5/01, Damon Wood wondered:
What sort of situations (due to light of course) should I use it, in
preference of my SC 50mm 1.8. I am thinking along the same conditions as
the ones you presented with the wide angle lenses.
To my knowledge of physics, would I be correct saying (in some conditions)
that the SC has advantages with skin tones rather than MC lenses. Also,
when applying the MC lenses to night photography, how should they be used,
if at all.
Cheers again guys,
Good material on the OM listing at the moment. Keep it up guys.
Damo
Damon,
Don't think of AR optical coatings as "filters." They're not. They work
by creating an interference with the light waves passing through them. The
single-coating model on the front objective is probably the easiest to
explain. The single coating has an index of refraction between the glass
it coats and air. As light strikes the coating, some of the light is
reflected from the coating. The remainder passes through to the next
interface of coating and glass. Some of the light reflects from this
interface also and passes back out past the first air-coating
interface. The coating index of refraction and its thickness is selected
so that the light waves from the two reflections are now 180 degrees out of
phase and "cancel" each other. "Conservation of energy" states that it
cannot simply disappear! Nor is it absorbed. Where does it go? Past the
second coating-glass interface and into the glass. This is how an AR
coating improves light transmission through the optics it coats. Because
various ray paths are at different angles, and a coating is only good over
a portion of the visible spectrum, it's not 100 0.000000e+00ffective. Thus, light
transmission into the glass is not 100%, but for a single coating it's
improved quite significantly compared to no AR coating.
For a single coated lens, the coating works optimally in the yellow-green
center portion of the spectrum. Multi-coatings have the centers of each
coating spread across the spectrum (e.g., for three coatings, one would be
in the upper red, another in the green and the third in the lower
blue). This improves transmission better across the entire spectrum, and
this is why a multi-coating makes a slight improvement over a single
coating, but not nearly as much as a single coating does compared to no
coating. It also improves contrast slightly.
I suppose you might be able to measure the slight difference in spectral
transmission between single and multi-coated lenses of the same formulation
using sophisticated optical lab equipment. However, in practical
application I have yet to notice the difference except in very slightly
better flare control and then it's only under very difficult lighting
conditions prone to extreme flare. The one SC lens I have the most
experience with under high risk of flare is the 35/2.8 Zuiko Shift which
I've used for night photography in urban areas with many, very bright
pinpoint sources of light. No objectionable flare has ever been
observed. Refraction around the corners where the aperture blades meet
causes a much more noticeable star effect, the points of which are still
very, very small compared to the star filter I have.
IMHO, much more ado about SC versus MC is made than the benefit provided by
an MC lens. There are aspects of the lens design that have a much greater
effect on contrast and flare resistance than going from SC to MC.
-- John
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