Should I use a UV filter to protect my lens?
To filter or not?
This question is hotly debated amongst Leica users. Opinions usually fall into two camps - the "never" faction and the "only when you need it" group. Generally speaking, there are few Leica users who subscribe to the idea of always using a UV filter.
The reason lies with the high quality of glass used in Leica lenses. As these are made from special formulations designed to minimize flare and keep contrast and sharpness as high as possible, the last thing you want to do is add another reflecting surface out the front.
UV protection is built-in
Leica claim they specially coat the front element of their lenses with UV filtering compounds, making the need for a separate UV filter superfluous. To quote from Leica Fotografie International, Sept 6/99, p37:
High mechanical resistance and chemical permanence (as well as maintenance of the optical qualities ) is achieved by means of a special plasma deposition technology. The resistance and adhesive power of the outer layer is so good that there is little likelihood of damage by environmental influences or persistant cleaning on the part of the user.
Numerous abrasion tests have been carried out. There is one that uses a rubber eraser which contains up to 50% pumice-stone grains. The standard test is to rub backwards and forwards 20 times with a pressure of 1 kg. Afterwards, no scratches should be visible on the lens surface.
Sometimes you've got to use a filter
The above LFI extract is QED for the "never" camp. However… working pros know that some environments are so dirty and dangerous that sometimes a protecting filter is better than nothing. Hence they only use a UV when they think the front element of the lens could get damaged. This is the viewpoint of the "only when you need it" group.
Having spent so much money on a Leica lens, the last thing you want to do is use some cheap and nasty filter. Get multi-coated ones from either B+W, or Heliopan or even the new Super Multi-coated Hoya filters.
If you want to buy the "best possible" filter - get the new(ish) B+W "MRC" filters. They cost 40-60% more than the already expensive "standard" B+Ws, but they are pretty amazing. As Albert Knapp MD noted in Oct 2002:
The MRC filters are superior to the single or double coated and worth the price in the form of better contrast and less surface reflection. As […] mentioned earlier, you look through them and think there is no glass at all!! Just a brass ring. […]
FINALLY, BEFORE YOU PURCHASE, remember that B+W has a new type of filter ring called the "F-PRO". It is superior to the standard filter ring and is much thinner. B+W is still trying to dump - I mean sell - the old ring filters before those with an F-Pro mount and this explains my wait for some of the filters. Insist on the F-Pro especially for WA lenses.
There are "UV" filters and there are proper UV filters which actually filter out UV light! See the UV filter entry in Robert Monaghan's Top Ten Photographic Myths.
For a May 2002 discussion of what the "E" means in "39E", "55E" (etc.) filter threads, see: