Originally Posted by
Drew Wiley
Filters behind the lens, even gels, are a no-no unless the lens has been specially designed with that in mind. It's an utter myth that rear-mounted gels are going to give sharper images than modern coated glass filters mounted in front of the lens. Just the opposite. Gels smudge and crinkle and attract dirt and grit easily; and rear mounting is generally a bad idea. Yes, uncoated glass filters, perhaps routine back in Ansel's Day, do attract condensation and need cleaning way way more often than coated and multicoated glass ones.
In terms of position, graphics process lenses were designed for gel filter placement at the nodal point between the two cells, and often came with a slot to accept those along with optional Waterhouse stops. However, I get superb result with front mounted glass ones. Some truly big telephoto lenses have a built-in rotating contrast filter set installed at a specific internal position. But any lens actually optically engineered for rear-mounted filters would be a rarity.
Have you ever seen some of AA's classic 8x10 shots blown up more than a 3X enlargement? Well, I've seen a lot of those, and nearly all of them are quite unsharp by modern standards.
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