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I just set up a simple DIY dry box (air-tight box + silica gel) to store my lenses in. The silica did a good job and quickly reduced the humidity inside the box to ~10%.

From what I read, recommended storage humidity is typically around 40%, so I'm now wondering if keeping them too dry could actually damage them in some way. The information I found so far is a bit contradictory/inconclusive.

So, is it a problem if I keep them at 10% humidity or is everything okay?

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    \$\begingroup\$ How long do you intend to just store them? Do you ever intend to use them? How often? I'd be wondering about lubricants drying up. Lenses need to be exercised. \$\endgroup\$
    – osullic
    Jan 13 at 11:19
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    \$\begingroup\$ 40% is much higher than some climates are. \$\endgroup\$ Jan 13 at 15:22
  • \$\begingroup\$ @osullic Varies depending on the lens. Some are used at least every few weeks, one only once or twice a year and one I'm actually considering to sell as I haven't really used it in years. \$\endgroup\$
    – luator
    Jan 15 at 8:11

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According to Zeiss, humidity levels below 30% is "dangerous for the instrument". About the only thing I can think of that might be affected by very low humidity is the adhesives used in bonding lens elements; most things in a lens are much more affected by oxidation than humidity (lubricants, plastics,rubbers, etc). But there is probably more involved that I don't know about... So I would take Zeiss's statement as fact, at least regarding some lenses.

How can fungus be avoided?

Reduce the relative humidity to less than 60% (never under 30% as it is dangerous for the instrument) by storing:

Zeiss also states that for humidity to be problem it needs to be over 70%, for more than three days, with no/very little air movement, and darkness. Your DIY box is probably creating two out of three of those conditions. Whereas those are not conditions that typically exist in most environmentally conditioned homes. If those conditions do not exist in your home, then I would have to say that the DIY dry box may be doing more harm than good...especially since it's not really needed.

Relative humidity of at least 70% (more than 3 days)

No or little airflow

Darkness

Link to the Zeiss article

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  • \$\begingroup\$ Where I live humidity is often well above 60% (at least in summer), so not that far from the critical 70%. So if possible I'd stick to the dry box, but I'll try if I can regulate the humidity by reducing the amount of silica. \$\endgroup\$
    – luator
    Jan 15 at 8:27

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