alfredo pagliano wrote:
>Yellowish image due to the rare-earth glass element?
>
>
Some of the earliest M and OM system 50/1.4 lenses and the first series
of 55/1.2 lenses used a bit of a radioactive rare earth element in the
glass of one or more elements. The long term effect of the radiation is
that the elements turn slightly yellow. For color or B&W negative film,
it doesn't make a significant difference. For slides, it does create a
noticable color cast.
Reports are that the radioactive 50/1.4s were sharper in the center than
the ones immediately following them. It didn't take long for other
advances in optical glass and lens design to exceed these early lenses
without rare earth components.
The radioactivity was enough to easily register with a geiger counter,
but not enough to fog even fast film left in the camera. I believe one
of several threads in the archives in the last year or two talks about
much more moderate radioactivity in a couple of other early lenses.
Oly was not alone in this, There is a series of the Pent*x 50/1.4 famous
for turning quite yellow. There are two reported cures for the Pent*x
lens, letting strong UV light pour through it for an extended period or
<http://www.hermes.net.au/bayling/repair.html>.
Moose
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