--- Bob <[EMAIL PROTECTED]> wrote: > How much UV does the lens glass absorb with no UV > filter? >
Well, there's no simple answer because different types of glass absorb differently. And plastic aspherics are different still (likely absorbing even more than glass). But, if I remember correctly my long ago optics unit in physics, typical optical glass probably absorbs about 50% of UV IN EACH ELEMENT. So a 4 element lens would pass only about 6% of total UV. You can imaging a modern zoom lens with 12 to 15 elements passes essentially none. This begs the qestion: why buy a UV filter, then? Turns out the absorption is related to the frequency of UV light. Here's an interesting web page: http://www.bobatkins.com/photography/technical/filters.html It says, in part: "So if you buy a UV filter, you'd expect it to block UV right? Well, sometimes you'd be wrong as the results of this test show. I've looked at the range between 350nm and 400nm for UV blocking *** since the glass used in almost all lenses will itself block any light with a wavelength shorter than 350nm,*** so you don't need help from a filter there." The UV range begins at about 400nm, so there's a tiny range of UV radiation (350-400nm) that is passed by normal lenses. It's this range that UV filters are supposed to reduce. But as the web site referenced above shows, not all do. Hope this is useful, Bob Meyer I don't suffer from insanity... I enjoy every minute of it. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
