One of the most frequently asked questions I hear is, "Should I use a protective filter on my lenses?"  My short answer is, "Yes."  Allow me to explain.

"Protective filters" usually refer to either a clear filter or a UV Haze filter.  These are attached to the threads on the end of the lens to protect the lens’ outer glass surface from minor impacts, abrasion, dust, moisture, salt water, etc.  For proponents, the theory is that it is cheaper and better to clean or replace a removable filter, than expose the lens to accidental damage.

Opponents to filters use the argument that placing another glass element in the optical path degrades the performance of the lens, as the lens’ designers had not allowed for the additional element in their design calculations, as well as creating an additional air-to-glass surface.

While it is true that the lens designers did not include the filter in their calculations, they did include the threads for us to attach filters.  If they did not intend for us to ever attach a filter, then they wouldn’t provide us with such convenient means to do so.  Furthermore, if we follow the argument that if it wasn’t designed in it shouldn’t be included, then we’d never attach any other type of filter, such as a polarizer or warming filter.  Yet these are used commonly and without question.

I have always found the "additional air-to-glass surface" argument questionable.  Every glass surface inside a lens is inherently an air-to-glass surface.  The only way to avoid this would be to have the interior of the lens a vacuum.  While lenses are "sealed" to prevent the intrusion of dust, dirt, and moisture, they still contain air.  Otherwise, we would never have to worry about condensation inside our lenses, as condensation cannot form in a vacuum.  Lenses are assembled in clean rooms, much like NASA uses, to prevent dust, lint, etc., from getting inside at the factory.  They have sufficient "sealing" to keep larger particles from intruding, but they are not "hermetically sealed".  If you immerse a lens in water, it will fill up in short order.  (DISCLAIMER:  Do not try this at home!)

So while I remain skeptical of the arguments opposing UV or clear filters in general, I do agree that poor quality filters will degrade optical performance.  I have seen people spend thousands of dollars on their camera bodies and lenses, and then throw a $20 filter onto a $5000 lens.  Even the most expensive filters, and the cost is directly proportional to the size of the filter, don’t cost more than around $200.  Doesn’t it make sense to always put the best filters you can get on your lenses?

For some photographers, a camera and lens are tools that are disposable.  If they get damaged or lost, they can be replaced.  I had one instructor who used to attach very expensive equipment to the top of sailboat masts or automobile exteriors to get a shot.  He usually did get the shot, and made tons of money because of it.  To him, the tools were expendable, because the return was worth it.  Equipment losses were part of the cost of doing business.  For me, the loss of a lens or body is rather more significant.  All of my lenses are protected by UV filters.  I have done this ever since my second 35mm SLR, which was a Minolta XD-11.  (A hot pro camera at the time!)  One day I dropped the camera, which landed right on the end of the lens barrel.  The filter was broken, but the lens and camera were undamaged, and I used both for many years.  Since then I have always used UV filters, because I would rather spend up to $200 on a new filter, usually much less, than buy a whole news lens.

I strictly use, and highly recommend, Heliopan filters.  Heliopan glass filters are made exclusively with glass from Schott (Zeiss) the world's finest optical glass supplier.  Heliopan filters are "dyed in the mass", and ground, polished, and coated to the highest standards. All Heliopan screw-in type filters are mounted in precision black anodized brass rings to eliminate binding or cross threading, and to ensure optimal alignment. The care, quality, and performance of Heliopan's filters make them the world's finest.

Besides the usual range of filters, Heliopan supplies 16 different types of polarizers, Zeiss Softars (always made of acrylic), graduated wide-angle filters, digital and video filters, and a full range of special effect filters.  All filters that will benefit from coatings are hard coated on both sides, and 16 layer multi-coatings (SH-PMC) are also available on many Heliopan filters.  Heliopan also offers a complete range of step-up rings for filters up to 105mm, and lenses as small as 27 mm.

I recommend the SH-PMC version of the UV filters, and have them on all my lenses, with the exception of one.  It’s more expensive than the regular version, but I think it’s worth it.  I also use the Heliopan circular polarizers.  I’ve tried others, but always come back to Heliopan, as I have always found them superior in all respects.

I mentioned that one of my lenses does not have a filter on it.  That would be the Sigma 300-800/f5.6.  And that’s only because, quite simply, nobody makes a filter that large (also the lens isn’t threaded), or I would get one!  The sight of all that naked glass makes me really uncomfortable…