> Karen, > > You are right in what you say about cut off, but it is not necessarily the > better filters, just those that are using the better UV glass. UV Glass is > listed as L types. There is L37 (used in many Nikon and Minolta filters), > L39 the standard for Hoya and L41 which is only found in Hoya's Super HMC > Pro1 Line. The number represents wavelength, for example 39 is 390 > nanometers or 3900 angstroms, and is the cutoff point. > Most modern lenses do not necessarily need L37 UV filters, but for those > times in high altitudes or near the ocean an L41 may help. For aerial > photography there is a B+W UV415 which is basically L41.5 glass and has a > slight yellow tint normal for glass above L41. This cast will appear in > photos taken at sea level. Incidentally, Canon filters are made by Tiffen. > Best way to check your UV filter is place it in a fluorescent > light source. > The filter should show a yellow cast. The stronger the UV (higher the L# > glass) the more yellow you should see. > As for me I use L39 or L41 as needed and I do own some Tiffen > Haze-2 filters > which if you look at have a very slight yellow cast to them. Good > filter for > higher altitudes, otherwise use a Haze-1 or standard Hoya UV. > > Peter K >
Hi Peter, I'm wondering if this information is posted anywhere. I'm aware that there are differences in the wave length of the filtered light but have not seen which filters use which glass. Also, is it only above L41 type glass that the yellow tint is visible? I have Hoya SMC, HMC and B+W UV filters and have not noticed any differences but now I have to go look! Thanks for any other info you can post here. Regards, Chip Louie * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
