Thanks Tom. Very well said and much better calculated. However, unlike
you, to me it's still only one of n surfaces and the effect isn't
large... probably because my meagre photographs aren't good enough to
tell the difference in the first place... and fortunately I don't have
to make my living at it.
Chuck Norcutt
Tom Trottier wrote:
>
> Folks,
>
> Two issues with filters & coatings.
>
> 1. The issue is not the transmission rate, but rather the reflection rate. The
> difference between 92.7 and 91.3% transmission is not a meagre 1.4%, but
> rather
> an increase in stray light bouncing around in the lens from 7.3% to 8.70f the
> total light input. In other words, the increase in glare from 7.3 to 8.7 is
> 19%.
>
> 2. If the film has a 9-stop range, the lowest lite capturable in an exposure
> is
> 2**9, or 512 times, weaker than the strongest lite, or about 0.190f the
> strongest lite. If the overall glare adds just 10f the incoming lite across
> the field, most of the shadow detail will be obscured.
>
> Now, not all of the glare makes it onto the film. Some goes back out the
> front,
> some is absorbed by the black lining of the lens or camera. Some is
> intensified
> by optical effects, giving the pretty patterns when a light source is
> included.
>
> But any reflections will add fog & reduce contrast all over the film.
>
> I can do without a 19 0ncrease in glare. Especially in low light situations
> with mucho shadow.
>
> Tom
>
>
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