[Leica] WTB: IR/UV filters

[henningw at archiphoto.com (Henning Wulff)]

At 9:45 AM +1000 9/4/10, Geoff Hopkinson wrote:

>Why do you think that the filters would likely shatter into a million ultra
>sharp pieces? Good ones at least are laminated materials.
>

At present only polarizers are still sometimes laminated; most others 
are dyed in the mass. The latter would shatter.

In earlier times coloured filters were laminated because the dyes 
could be controlled better in gel form than as dyes added to molten 
glass. They were abandoned when dyed in the mass became possible 
because the gels tended to fade relatively quickly, and they 
necessitated thicker filters which caused a lot of plano-parallelism 
problems. I once (in the 70's) checked about 50 filters; over 75% of 
the laminated gel types had surfaces that weren't perfectly parallel 
which would cause serious problems with some lenses. The gels also 
didn't really provide any structural strength; not like the vinyl in 
laminated safety glass.

As far as the UV filter argument goes, the filter ring ding vs. lens 
rim ding I can understand, but my lens shades do an even better job 
and they shade besides. Also, if you shatter the filter after 
whacking the lens against something, it does not necessarily follow 
that the front element would have been damaged if the filter had not 
been there. Maybe yes, maybe no.

As you might guess from the above, I use filters when there is a good 
reason, but leave it off otherwise. I did some tests once which 
showed that under some circumstances the images gets slightly 
degraded when a filter is used. Not often, but still...

If you use a filter, make sure the coatings are good. It doesn't have 
to be the most expensive one.

-- 

    *            Henning J. Wulff
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