[Leica] UV filtration

[nfrnkish@dux4.tcd.ie (Neil Frankish)]

I have read with varying degrees of interest, the UV filter debate
(again!). I have heard about multicoating, of special glue in the lenses
which blocks UV etc. I must confess to being at a bit of a loss in regard
to this. I far as I am aware, glass blocks UV, from greater than 300nM
down, which is why, when you use a UV/visible spectrometer, you need to
change from glass to quartz cells when you get to around 300 nM. Does
anyone at what wavelength a photographic filter will "cut in"?

Presumably, a UV filter (esp. one of glass) must filter at greater than 300
nM, otherwise there would be no point. Is that the point?  :-)

Or maybe leica optical glass blocks somewhere lower than 300 nM

*If* I had a UV filter, I could put it in the light path of the UV spec.
and find out! The lens caps that I use block everything.

Neil.

p.s I have just noted that in the 51st ed. of the Chemical Rubber Co.
Handbook of Chem & Phys, there are several Corning glass filters which are
described as clear UV transmitting, but transmission below 300 nM ( eg for
glass no. 0160) is negligable. So UV filters must filter above 300 nM.

pps
Furthermore, the Kodak Wrattan UV filter No.1 blocks below 360.
Borosilicate glass cuts off at 330, Heavy flint glass (whatever that is)
transmits only 58% at 384, so we have overlap, depending on the glass.

Did anyone want to know this? probably not. I wonder if I could fit a lens
into the UV spec. chamber?