I live in humid Japan, and my camera and lens storage cabinet has 50 percent humidity all the time, but it's not bad.
Originally Posted by Timothy
If it goes up to and stays around 80 percent, I will be a bit worried about the fungus.
The best thing you can do is not to leave the enlarging lens(es) in the humid and dark environment all the time. If you have already seen a sign of fungus growing inside the lens(es), you will need to get it clean soon.
I have my darkroom in my basement. It can get damp down there, so years ago I bought a de-humidifier, which is about ten feet away from the door to my darkroom. Never a problem with fungus.
Back to freezing lenses, strickly from an academic point of view, while I have never intentionally set out to freeze a lens, over the past 25 years, I have used telescopes (refractors & reflectors), binoculars, and cameras in sizes from 35mm, 120mm and large format outside, at night, in cold Canadian winters, sometimes at -20C.
While I have had the grease and/or lubricant used in the mechanical part of the lens or mount or shutter get sticky in the cold, I've never, ever had any optical problems with any lenses. In fact, come to think of it, I even left a microscope in the car overnight one winter, and it froze up real good too, but it still works fine to this day - and it's a 85 year old microscope too!
The only thing I ever had "die" on me in the cold was batteries, even the meter once died in my Nikon FM because the cold killed the battery. But I could still shoot just fine.
Try doing that with digital.
keepint the lens in a CLOSED box with a few THymol crystals should prevent fungus growth.