Flare is just unwanted light bouncing around inside a lens that doesn't
contribute to your image. It might come from 1/light hitting a reflective
surface inside a lens, 2/scratches, dirt, etc. on glass, 3/lack of lens
coating (as you mention), and 4/lens aberrations such as a second image of a
bright object inside your field of view. Multicoating of lens elements only
helps as to #3. And you're entirely correct, flare is an effect, not a cause.
One flare test that is used is to shoot the inside of a black box which is
mounted to a white wall. The difference between the densities on the negative
should give you some idea of the generalized flare resistance. A flare
situation is similar to this, i.e. when there is a bright source of light
either inside or outside the picture area that reduces the general contrast
of your photo. A hood can help if the source is outside of the picture area.
A perfectly flare resistant lens could be used to take a backlit portrait
with the sun also in it.
Warren
l> I accept
> it that flare can't really be cleaned up by anything, but I don't totally
> understand why because I really don't understand the nature of "flare
> conditions." In other words, I understand descriptions of what flare is in
> a lens, but I don't really understand exactly what causes flare to happen.
> Flare in a lens is an effect, not a cause, even though we sometimes talk as
> though the lack of multi-coatings "causes" flare. Joel
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