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[OM] FW: [Cameramakers] Sun bleaching yellowed lenses

Subject: [OM] FW: [Cameramakers] Sun bleaching yellowed lenses
From: "Wayne Harridge" <wayneharridge@xxxxxxxxxxxxxxx>
Date: Wed, 9 Apr 2003 21:55:21 +1000
An interesting posting on the cameramakers list.  I hope it's not bad
netiquette to forward it to here.


-----Original Message-----
From: cameramakers-admin@xxxxxxxxxxxxxxxxxx
[mailto:cameramakers-admin@xxxxxxxxxxxxxxxxxx] On Behalf Of Kelvin
Sent: Wednesday, 9 April 2003 9:06 PM
To: cameramakers@xxxxxxxxxxxxxxxxxx; NikonRepair@xxxxxxxxxxxxxxx;
camera-fix@xxxxxxxxxxxxxxx; camera-fix@xxxxxxxxxxxxx
Cc: Charles_Lau@xxxxxxxx; Parlin 44; Lieu WL; ClubM42@xxxxxxxxxxxxxxx
Subject: [Cameramakers] Sun bleaching yellowed lenses


Hi guys,

this may be of interest to some of you who have yellowed lenses ... for
me,
besides my super-takumars it is my nikkor 35/1.4 pre-AI. Apparantly you
can
wrap your lens in foil, front cap on, and face the rear element to the
sun for
a week and it reduces the yellowing (if not eliminate it).

I attach the post. This is an exciting development.

Gene: If you're on the list... maybe you can elaborate..?


Message: 1
   Date: Tue, 08 Apr 2003 09:03:42 -0700
   From: Gene Poon <sheehans@xxxxxx>
Subject: Sunlight vs. Yellow Peril: IT WORKS!

About the experiment to see if sunlight would bleach Yellow Peril, the 
radiation-caused yellowing of internal elements afflicting the 7-element

50/1.4 Super Takumar, Super-Multi-Coated TAKUMAR and SMC TAKUMAR lenses 
for the Pentax Spotmatic cameras:

IT WORKS!

It has only been since Thursday, April 3 that I put two 50/1.4 Takumars 
on the windowsill.  Since then, every day except Saturday has been at 
least mostly sunny here in Northern California.  Today I got a bit 
impatient, and besides, I had to go into the box containing my Pentax 
M42 stuff anyway, so I figured I may as well find out what was happening

and get out the rest of the 7-element 1.4 lenses to start on them, if 
the sun bleaching was actually proceeding.

The experimental subjects were my very yellowest Super-Takumar and a 
Super-Multi-Coated TAKUMAR which was moderately yellowed and had filter 
ring damage and slightly stiff focusing.  I figured I should experiment 
with the two worst lenses, in case something bad happened.  The UNCAPPED

lenses got completely wrapped in aluminum foil except for the rear 
element, to reduce heat buildup in the sun, and also because doing so 
would reflect light back through the lens, hopefully attacking the 
yellowing from both sides.

This morning, after only five days, I unwrapped the lenses, and compared

the two experimental subjects with the rest of my 50/1.4 Takumars.  THE 
SUN BLEACHING WORKS!  The two experimental lenses are now the least 
yellow (the comparison is not even close) of all my 50/1.4 Takumars 
except for the very early, 8-element Super Takumar that is not prone to 
yellowing.  Compared to that lens, and to the 55/1.8 and 55/2.0 lenses 
which also are not prone to yellowing, there is still a slight tinge of 
yellow, about the same as the pink tone from a weak skylight filter. 
They are being rewrapped for another stay in the sun, and the rest of my

yellow Takumars are going to join the first two on the windowsill in a 
few minutes.

Probably many Pentax M42 collectors and users will have Takumars  on 
their windowsills, very soon if not already!

-Gene Poon



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