Coatings serve two purposes. The front facing elements are coated to
maximize transmission through the lens to the film/sensor. The rear
facing elements are coated to facilitate transmission in the opposite
direction... back out of the lens such that the reflections that do
occur despite the coatings don't reflect back again. It takes coatings
on both surfaces to be effective. Multi-coated surfaces have
diminishing value on primes with only a few elements. A single
multi-coated element such as a filter added to a zoom lens is of
vanishingly small value relative to a single coated filter. The
additional light loss or reflection of single coated vs. multi-coated
for a single element would be difficult to measure... probably on the
order of a percent or two.
Chuck Norcutt
Bill Pearce wrote:
>> My personal opinion is that this is a bunch of hooey. If you have an AR
>> coated filter (even an old one) it should be coated on both sides.
>
> My initial, uneducated reaction is to agree with you, and I have seen no
> information to change it. The one thing that bothers me is that some filter
> manufacturers might have been blowing off the back side as a cost savings
> without sharing that fact.
>
> I have always believed that all surfaces of modern (by that I mean since
> multi coating) lenses have been coated. Older single coated lenses may or
> may not have. A simple three or four element lens may profit less from
> extensive coating.
>
> Bill Pearce
>
>
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