Monday, 21 April 2008

humidity and cameras

Most people don't realise that Fungus grows on camera lenses. For example this page explains this a little. Fungus attacks camera lenses in storage, and its growth is related to humidity. So people who are a little more in the know often speak of removing humidity with Silica Gel. I've found this is not a sound practice for anything longer term than a few weeks. Given the regularity of this discussion I thought I'd put a blog entry here about it.


If it remains below 50% then fungal spores will not germinate (as far as I've read). Keeping it below 30% risks dammage to your camera as the lubricants and foams will start to 'dry' ... yes, even salt crystals have water in their stucture and you can get anhydrous salt powder.

I lived in a semi tropical area, I had already lost a lens to fungus (a 50mm Zukio macro) from my Olympus from fungus (I often visit rainforest in the rain). I had started a business and bought some lenses worth quite some thousands of dollars (IE: TS-E 24, 90, and some large format lenses). I thought it prudent to conduct investigations.

I have a friend in the army who is a munitions specialist and he has reported to me that for their purposes silica gel was insufficient to maintain correct humidity. So wondering what this translated to in a quantitative manner I did the following experiment (if you google this on google groups this you'll find the results published back in the late 2000 on

Humidity Experiment with Silica Gel

  • ~20g/100cc of Purple indicating silica gel
  • heavy duty "zip seal" plastic bag (1 liter capacity)
  • glass vegemite jar
  • electronic hygrometer


I thought I would test using a common zip seal bag, since cameras are often placed in these for protection. Since the camera in the bag occupies some space in the bag (and prevent the bag from being slim or vacuum sealed (if they indeed can be), I placed my sample of silica gel into a (lidless) glass jar with an electronic hygrometer hopefully replicating storing a 35mm camera lens in the bag.

The bag was only containing air from the room, no other gases were placed into the bag (such as gas from cylinder of nitrogen).

The bag was then zip sealed. The jar was put on its side, so that the top was not blocked further by the plastic and the hygrometer was visible with out disturbing the setup for making observations.

Note: The hygrometer displays LL% when out of range at the low end of humidity (which was cited as ~30%RH by the maker) and HH% when over 90%.
raw data

23-Mar-00 68% 6:38:00 PM experiment started
23-Mar-00 41% 8:52 PM
24-Mar-00 LL % {very rapid absorption depletion of humidity in bat}
25-Mar-00 LL% {already seems to be loosing the colour in the crystals, some are pink]
26-Mar-00 LL% {more of the crystals seem to be pale pink}
27-Mar-00 LL% {more of the crystals seem to be pale}
29-Mar-00 32% {most of the crystals are pink}
31-Mar-00 39% {more seem pale, a few are still dark}
02-Apr-00 43% {no apparent change in the crystals}
03-Apr-00 45%
04-Apr-00 45%
05-Apr-00 48%
06-Apr-00 50%
09-Apr-00 52%
10-Apr-00 52%
11-Apr-00 54%
13-Apr-00 57% {almost all crystals are depleted, about 9 remain as pale purple}
15-Apr-00 60%
17-Apr-00 64%
18-Apr-00 66%
24-Apr-00 64%
27-Apr-00 73%
29-Apr-00 76%
experiment concluded duration = 22 days.


Figure 1: humidity measurements


As you can see, even in a small zip sealed bag the humidity rose to a point where the silica gel was failing to cope with humidity migration across the membrane of the plastic, and simply maintaining a constant level in the bags environment. Since silica gel can also release the humidity it then becomes a 'buffer' keeping the humidity reasonably constant (perfect for those fungii and molds) when the outside ambient humidity goes high. Typically this goes high in the night (as the air cools) and low in the day (as the air heats up).

Storing stuff inside your house (often cooler than outside) in a tropical area will ensure a nice humid atmosphere for your fungi. Meaning camera bags placed in cupboards are the worst locations.

Based on this I constructed my own humidity cabinet from a peliter effect device (commonly used in electric 'car fridge' systems) to condense the air and drain it out of the cabinet.

My power supply is a $15 cheapie 8 amp 12V car battery charger and a $20 12V GEL cell (to even it all out). I then ran a simple 24 hour timer circuit (like used to turn lamps on and off) to shut off the entire thing at different times of the day (used a relay to kick in on the 12V side of the car battery charger to shut off the power from battery to Peltier too). I made the back wall of the cabinet 5mm ply and cut out a shape to take the peltier in the middle. This puts one side of the heat sink inside (that'll be the cold side) and the other outside.

You'll need to fiddle with heat sinks to get the right efficiency, but I settled on this pair:
inside and outside

Then I made a simple catch tray (for the drips) out of a cut down plastic milk container and ran a bit of aquarium pipe out of the cabinet to drain it. Careful with this as in my summers I get about 500ml a day on a good humid day!

Naturally you need to be a bit handy, and have some electronics knowledge too. Of course you could buy one of the pre made ones.

hope this helps

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