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Old April 1st, 2005, 01:36 PM
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Patman10 Patman10 is offline
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Use of filters- Reprint the faults of UV filters

The Filter Flare Factor

by Mike Johnston

The Sunday Morning Photographer — a weekly photo.net column: Feb 6th, 2004

Do you use a "protective filter" on your lens? I encourage you to take that filter off your lens and leave it off.

This is, of course, one of those perpetual nit-picky arguments photographers indulge in. You know, like whether Nikon or Canon is better, whether Leica lenses are worth it, whether you should use a tripod with 35mm, and so forth. This is just my answer for it, and may not be yours. But I'll make my case.

In the old days, often the objectives (front elements) of lenses were made out of glass so soft that merely by cleaning it overenthusiastically you could make tiny scratches on it. (Especially if — and this shows the changing of social customs over time — you were in the habit of rubbing your lens with the end of your tie, as many working photojournalists did in ye olden days when men almost always wore ties when appearing in public.) Also in past times, lenses passed UV light, which could throw off TTL (through-the-lens) light meters and/or cause film to respond in weird ways.

The solution seemed both elegant and sensible: use a UV filter to both cut the UV transmission and protect the objective from scratches. That's been a part of photography's "received wisdom" ever since.

Here's the news flash, though, although it's not exactly news, since it's been true for a good long while now: good modern lenses have very hard glass objectives, and/or scratch-resistant coatings. They make it difficult to scratch or mar a lens. With reasonable care, and perhaps a decent lens hood for physical protection if the objective is not recessed, there is almost no chance you will scratch the objective of your lens. Empirically, this is confirmed when you survey used lenses for sale. How many do you find that are scratched? How many eBay auctions for lenses don't say "glass mint" or "glass perfect"? Don't overestimate lens owners: if it were so easy to scratch up a lens, there would be a lot more scratched lenses out there than there are.

Incidentally, if by any chance you do manage to get a small imperfection on your lens, try this trick to put your mind at rest. This is something I learned from the legendary Pentax technical guru and Mensch of the Mountain Don Nelson. Tear a corner off the sticky part of a Post-It note so that you've got a bit of paper about the size of a pea. Stick it on your lens. Now look through the viewfinder. Surprised? Okay, so stop worrying about that little speck, then.

Modern lenses also pass very little UV. Either the glass, coatings, or even the cement used for cemented elements filter it. The so-called "hot mirror" filters are sharp-cutting UV blockers, but ordinary UV filters don't commonly help good lenses much, if at all.

There are a few exceptions. When you are shooting in actively hazardous environmental conditions, such as flying salty sea-spray or blowing sand, snow, or volcanic ash, it might be smart to use a protective filter that's easy to wipe clean. When you're in an an environment rich in ultraviolet, like at the top of a Swiss Alp, take a hot mirror filter along. Obviously, if you want to polarize the light, add a color, or cut the amount of light reaching the lens by a measured amount, don't hesitate to use the appropriate filter.

One truly useful new technology is Schneider-Kreutznach's new MRC coating. These new filters in Schneider's B+W line use a Siloxan coating that acts like a permanent treatment with Rain-X, resulting in much lower surface tension, allowing the filter to shed dirt and water significantly more easily. This is the filter to own for shooting in the rain!

I learned from David Vestal that the longer you're a photographer, the more likely you are to accept the peculiarities of camera vision: motion blur, selective focus, and (in B&W at least) the somewhat unnatural blackness of shadows. But the look of rain droplets on the lens is something I've never liked, although like any "flaw" it can be expressive when used with good judgment.

At any rate, I love it when a new technology a) actually works, and b) actually works for a useful purpose. I recommend MRC filters when you're shooting in the rain.

pic3.jpg (10878 bytes)

Otherwise, why pay for an excellent modern lens and put another sheet of glass over it? Would you be happy shooting all your pictures through a windowpane?

I'm sure there are crestfallen filter-aficionados out there wondering why they can't use their precious filters. What can it hurt?

Well, it's not a sin, so do it if you want to. However, there is indeed a reason why not to use filters. It can be seen in Adam Gori's pictures below, in which filter reflections or filter-flare have caused ghosting. Filter flare commonly occurs directly opposite the optical axis (i.e., center of the frame) from an excessively bright light source.

pic1.jpg (39410 bytes)

Notice the bright streetlight in the upper left-hand corner. Now find the center of the image, which corresponds to the optical axis. At the same point along an imaginary diameter line, but opposite the streetlight, you can clearly see filter flare where you would expect to find undifferentiated shadow area.

This doesn't always happen by any means. But in some cases it's pronounced. The best example I've ever seen, aside from one of my own pictures that has such subtle shadow detail that it won't reproduce in a scan, is a picture in William Albert Allard's book about cowboys. Unfortunately, I can't find my copy, although I know it's around here somewhere. Anyway, the picture shows a lone building with a bright neon sign on an open prairie, with the horizon low in the frame. The picture was taken near dusk. Hanging in the sky, opposite the midpoint of the picture frame as I've described, is an inverted ghost image of the neon sign.

Obviously, if the filter flare happens to fall over an area where there are highlights or more confused tones, you won't see it. It can be pretty subtle. Take a look at Adam's picture below, where once again you can see faint filter flare opposite the bright light.

pic2.jpg (27096 bytes)

Ironically, the better your lens, the more desirable it is not to have a filter on it. Also, if you commonly shoot with a zoom with more than ten elements, a filter, even if it's multicoated, isn't doing the lens's inherent flare and veiling glare characteristics any favors. The more glass surfaces, the less the transmission, period.

So use a filter when you need one, and by all means get one of those slick new Schneider MRC filters if you ever shoot in the wet. Otherwise, use that UV filter like a lenscap, and take it off before you shoot.

—Mike Johnston
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Old April 1st, 2005, 06:53 PM
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Dolphinraver Dolphinraver is offline
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Interesting article.
Thanks for sharing.
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"The photograph is completely abstracted from life, yet it looks like life. That is what has always excited me about photography."
— Richard Kalvar

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Old April 1st, 2005, 09:37 PM
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Patman10 Patman10 is offline
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My pleasure!
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