Protecting the lens with filters?
Thursday, March 4th 2010 @ 3:23 PM (not yet rated)
I've had this asked of me MANY times ... should I protect my nice new lens with filters on the front of it? My professional peers (for their own work) are very strongly divided: this is the old beer commercial's "taste great vs. less filling" debate on steroids! I've looked at it very practically, and am quite comfortable with my advice, which is: some of the time, yes. How's that for a strident position!
It depends on the situation you are shooting in. In the studio, I do NOT want or need extra glass in front of that expensive lens, as it can't help and there's no chance of the lens's front element getting damaged. Out and about, now ... that's a different kettle of fish!
Many people don't realize that any "decent piece of glass", photog-speak for a good lens, will have many layers of coatings applied to the surface of the glass used in the lens at the factory. The front of the front element will have more coatings than probably any other "element" of the lens. These coatings help to cut down "flare" where light scatters around inside the lens, and this un-focused light bounces back to the sensor causing the image to be mushy from lack of contrast.
So when you get a scratch on the front element of your lens, you are actually scratching those precious and fragile coatings. Realistically, the only way to repair those scratches is to send the lens back to a repair shop for a new front element. This is an expensive problem! And also, this is where a screw-in filter on the front of the lens can help. Some filters, like the polarizing filters (shown in the illustration) do a specific and major "job" on the image. Some do only a tiny amount, as say, a "UV" (ultra-violet blocking) filter.
If you are in a situation of possible but not likely damage to the lens, then I'd suggest a very FINE quality UV filter screwed in to the front of the lens. It will make very little difference to the shot and could save you some serious cash. $35 to $100 for a filter (depending on diameter) can be a lot cheaper than replacing a front element!
If you are in a situation of fair likelihood of damage to the lens, say a wind-blown day on the beach (sand is a HUGE threat to your lens's coatings!) or where there is going to be a lot of phyisical jostling near the camera, use a modestly-priced UV filter, something in the $10-$25 range. The image quality may suffer slightly, though you may not be able to tell it from all the other things that (at that time) may affect image quality. And it the filter gets scratched or broken (and I've had BOTH happen a number of times!) you are out less cash than replacing that lens element!
