[vonBaloney]

I have heard at least a few people claim that after de-yellowing the lens regained some lost sharpness, so it might be worth doing for more than color reasons...

[elliott]

I used a UV lamp to de-yellow my Takumar, it didn't heat up the lens very much, I did use foil around the black barrel of the lens so it was reflecting light instead of absorbing it. If you decide to go the UV lamp route instead of sunlight, make sure you get a real UV light. A good indicator is if the lamp can be used to light a room, it is not a real one, it is a "party blacklight" and won't put out enough UV to clear the lens up quickly. Mine cleared up in 3 days, I saw an improvement after 24 hours.