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How do you explain the reflection of the Elks Lodge?

A couple of people were a bit puzzled by the reflection of the Elks Lodge seen in today’s page A-1 shot of an interior scene in Old City Hall. Here’s how it came to be.

The landlord wouldn’t allow us inside Old City Hall, so I snooped around for windows to look into and found a vacated photographer’s studio in the northwest corner of the building across Commerce street from the old Elks. When shooting through a window we usually want to eliminate any reflections so the camera lens is pushed up against the glass.

That’s what I did for a couple of frames, then I noticed that when I pulled back from the window a couple of inches, the white Elks Lodge in the bright sunlight behind me popped into view on the left. I still didn’t want reflections elsewhere in the shot, so I rearranged my arms, head and torso to block the view of other sunlit things behind me. So, in theory, in this shot there are also reflections off the window glass of my camera, hands, head, arms, et cetera, but all that stuff was in deep shade and not bright enough to actually show up in reflection.

What about a polarizing filter?

They are occasionally useful for eliminating reflections, but only in a very limited way. Reflections can be blocked by a polarizer if the light in them is polarized, and light is only polarized by reflections at certain angles. Recalling college freshman physics (you remember, don’t you?), reflected light is 100% polarized only at Brewster’s Angle, which, for an air-to-glass boundary, is not far from 45º. So when shooting through glass obliquely one can benefit from a polarizer.

But there’s another limitation on top of that. Most shots attempted through glass are with a wide angle lens, so for much of the frame, the angle of view toward the glass is NOT at Brewster’s Angle. The result is that the reflection is eliminated by the polarizer in only one spot in a wide angle photo and the rest of the reflection is effectively undimmed.

It’s easy to see this without a camera. Stand outside a window in the daytime, or inside a lit room at night, look through a polarizer (rotating it to whatever orientation is needed), and you’ll see the fuzzy-edged spot on the window where there’s no reflection.

And I can’t resist another polarizer tip here: they work well for deepening a blue sky, but, similar to reflections, only at a certain angle. Light scattered by our atmosphere (the blue light in a blue sky) is maximally polarized when viewed at 90º from the sun. When you look through a polarizer at other angles, the sky is little affected.

The practical way to predict whether it’s useful to deploy a polarizer on a sunny day is to point toward the sun, then sweep your other arm around while holding it perpendicular to the first one. You’ve just defined a “great circle” around yourself where the sky is maximally polarized.

These are some of the limitations that explain why I only use my polarizer about once every few years.

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