dmmartindale@watcgl.UUCP (Dave Martindale) (08/23/84)
When I first got into photography, about 15 years ago, camera lenses (and filters) typically had one layer of anti-reflection coating on each glass surface that was in contact with the air. Then along came Pentax with their multi-layer coating, and soon everyone else was multicoating their lenses too. Multicoating apparently gave about as much of a gain over single coating as single coating did over a raw glass surface. And, apparently, multicoating is absolutely necessary in current-days zooms. With 20 or more glass-air surfaces, a zoom without multicoating would have poor contrast because of all of the reflections, and would also transmit less light. But most filters still seemed to be single-coated. I'm in the habit of keeping a skylight filter on my lenses to protect them, and it bothered me that the filter seemed to reflect several times as much light as the glass surfaces of the lens it was on - the coating was clearly not nearly as effective. Then I became aware that multicoated filters were available at, of course, a premium price. I went out and bought Hoya multicoated filters for my zoom lenses, which I figured needed them the most. They clearly reflect much less light than the filters they replaced, though they are still not as good as the coating on my current-production Minolta lens. My housemate recently bought a camera, and received a Minolta UV filter as part of the package. Examination of it reveals that the coating on it is slightly better than the multicoated Hoyas. So, it seems that Minolta filters are now multicoated, and perhaps all Hoya ones are. And I've seen filters made by B+W that were multicoated. But none of these were labelled as such. Comparing filters that I have access to, the new Minolta filter is best, followed closely by the new Hoya filters. The next best is, surprisingly, a 12-year-old Hoya filter that I bought with my normal lens. Then comes a filter labelled "Avigon" which was included as part of a recent lens purchase - it is considerably worse than the old Hoya. A 3-year-old Vivitar filter is slightly worse than the Avigon. Finally, a "HCE" filter that is 12 years old is much worse than the Avigon - it behaves as if its rear surface has no coating at all. So, what is going on? Is the 12-year-old Hoya multicoated too? Why aren't manufacturers labelling their filters as multicoated? I would think that this is often the major difference between filters of good and just ordinary quality. How important is the quality of the coating anyway? How much will the image contrast be degraded by the presence of one poorly-coated glass surface in the optical path? There is one moral: All brands of filter are definitely NOT alike. Dave Martindale