Re: Protecting the lens

A large proportion of SLR users lace the front of their lenses with a
permanently-fixed cover. Most people use UV, Skylights or simply blank
plates of glass.

UVs filter out UV radiation from entering the lens, which is supposed
to make some kind of difference, but I've never noticed it. Skylights
are like UVs but have a very slight red tint to them, which is only
visible if you put it against a white *** of paper. Alters the colour
ever so slightly. A blank plate of glass is just a blank plate of
glass. :)

All are factor 0, which means that they do not alter the amount of
light entering the lens by any perceptible amount (typically they let
through 98%-100% of available light as compared to a naked lens).

Technically speaking, extra layers of glass alter the optical quality
of the final image. A filter is an extra layer of glass. But
personally, I think you'd need to have the most discerning of eyes to
see the difference in raw image quality between a filtered and
unfiltered image if the filter is half decent.

The benefits of having a filter were very real to me when I made the
mistake of getting accidently inebriated while shooting in Barcelona,
and the resultant clumsiness ended up in one of my expensive lenses
hitting a table. The filter shattered and got destroyed. The lens?
Fine. I don't know how much actual impact the filter took, but it was
assurance enough to make me promise myself to always have a filter on.

Also, every three years I get new filters for all my glass. Why? They
get pretty scratched up - scratches that would have been elsewhere had
the filter not been on as a photographer's ozone layer.

.