Storage of optics below 30% relative humidity. Really bad? Myth?

Hi all,

 

I've recently crossed with humidity issues:

 

(1) Humidity has been running around 100% RH inside my home, and I have finally made a dessicant chamber for all

of my optics to live in. I'm using Drierite DuCal, which of course grabs all the moisture it can. Moisture has been

drawn from the equipment and materials for the past several days (including the partitions in the chamber, which are

made of wood), and the humidity has now fallen to about 25% RH, according to my humidity strips. It will of course

fall further.

 

(2) I read this the thread here (http://www.photo.net/canon-eos-digital-camera-forum/00Qziv) and followed Mark U's link to

a Zeiss page on lens fungus here (http://www.zeiss.com/c12567a8003b58b9/Contents-

Frame/29cd78d56723da79c12571180042df52), whose advice he says we should beware of. On that page, Zeiss

says humidity should be maintained no lower than 30%, as ultra-low humidities are "dangerous for the (lens)." They

don't elaborate.

 

This issue of dry storage had come up earlier in another thread here (http://www.photo.net/canon-eos-digital-camera-

forum/00PDFq), in which Chris Eastwood and I had a great discussion about humidity control methods. He made the

same assertion about RH below 30%, defending that lower RH might dry up greases and dry out foams. I asked him

if he knew of an authoritative source for that info, and he didn't, saying it was just something he had heard. To put

this into perspective, I once lived in a VERY low humidity desert environment, and I don't recall the low humidity

harming anything. I still have optics I owned there in the 60's and 70's, and they're in great shape. The drying grease

argument shouldn't have anything to do with RH, and foams deteriorate from rot, rather than moisture loss.

Irrespective, there are no foams in lenses, as far as I'm aware.

 

So I'm again wondering where this 30% guideline came from and whether it really has any merit. Does anyone know?

 

The reason I'm wondering is very simple: It makes all the difference as to how I need to dehumidify my optics. I can

continue to use DuCal dessicant in a sealed chamber, but the moisture-hungry material will drive the RH far below

30%. I can perhaps get a fancy DuCal chamber that opens and closes, combined with lots of silica gel to buffer the

RH at my chosen humidity. I can also set up a peltier dehumidifier and a humidistat in an old refrigerator (not

running, of course), to maintain RH at the desired setpoint. The simplest method is to use the DuCal just as I am,

but I obviously don't want to do it if it will harm the equipment in any way. I've known other people -- colleagues of

mine in the sciences -- who have stored their optics in glass dessicant chambers sealed with vacuum grease in

ultrahumid environments. Those individuals haven't experienced equipment damage, to my knowledge.

 

Anyway, I would appreciate any information anyone has to offer on this subject. I've searched for it, just like Chris

Eastwood, and I've come up "dry." (Excuse the play on words!)

 

Thanks to all!

 

Peace, Sarah

Low humidy won't affect the optics of a lens, but as Les comments, it's possible that it could affect some of the other construction materials. It is known that some types of natural rubber show accelerated hardening under low humidity conditions.

There might be some affect on lubricants. Do a check on how museums store furniture and artwork. I believe it's in the 30-40% range, and some in the 50% range.

Low humidity should not be a problem, remember, they pack a new lens with desiccant to keep it dry.

I'd be a lot more concerned with mold and fungus in the house/apt with a RH around 90% than the air being a little on the dry side in the optics storage container.

The other day my friend who is learning English said there is too much humility in his basement!

Fungus won't grow under 70% of humidity I think. I keep my stuff in a dry cabinet, there the level of humidity is between 30 and 45%, my stuff has been in perect shape for more than 2 years. i think 705 is the number to keep in mind.

Thanks, everyone! I've checked Las Vegas seasonal averages, and I have to admit that's one bone-dry city! Wow!

 

Michael, I've heard many times about drying lubricants, but I've not seen anything to support the claim. Desiccant has no affinity for organic volatiles, and it is the loss of these volatiles that makes (older formulations of) greases dry and harden. Regarding furniture preservation, there is good reason not to dry wood too dry. It's because it will shrink and crack. (I have to maintain my pianos at a constant 42% RH.) Similarly, canvasses will shrink if too dry, causing oil paints to crack. However, shrinkage shouldn't be a consideration with metal, plastic, or glass.

 

Les, Bob, everyone, should I be concerned with degradation of any of the rubber or plastic components of modern equipment, specifically Canon's? (I have other equipment in the container, but it's all metal construction.) I'm pretty sure all the plastic is polycarbonate, which I would imagine is very resistant to rotting/degrading. I do have my camera bodies in the container too -- a 10D, a 5D, an Elan 7n, and a 1n. All have metal shutters, of course.

 

I can see low humidity being a static discharge hazard, but certainly not without friction or air movement. If I reel off numerous frames with a bone-dry camera, causing the mirror to whoosh around inside the mirror chamber, could that be a static issue, particularly when the shutter opens to reveal the sensor? Of course the sensor is protected behind glass, which is an excellent dielectric.

 

Anyway, barring any major concerns about RH being too low, I rather like my setup, The chamber is made from a Cambro food transport box, which is tough, air-tight, and insulated -- a bit like Pelican cases in its construction, but heavier duty. I made a web of dividers for individual lenses out of luan plywood, cemented together with West System epoxy and covered in thin, closed-cell foam padding. My plan is to use this chamber for travel (e.g. camping) and to use a cabinet or unplugged frig with peltier dehumidifier inside for home use.

 

If anyone is interested, the DuCal is actually rather light for something that looks like cat litter, and it absorbs 25% of its weight in water. I put it into a paper bag, which I cut off and glue shut. Moisture exchange occurs readily through the craft paper. I haven't yet regenerated the stuff, but it's done by heating it for 2 hr at 450 F in a 1" deep pan. Sounds pretty easy. I've used it in other applications with great success. You have to buy it in 40 lb drums, but it's not very expensive. You can order it from the Drierite Corp in Ohio. Good stuff! :-)

In response to will dry air dry out lubricants ... In a most simple, yet fairly accurate comment, you can

regard 'perfect' lubricants as getting gunky (dried out,

increased viscosity, etc.) principally from one main source. Oxidation. Relative humdity does little to alter the rate at

which volatiles escape from the lubricant. Oxidation seems to be a top reason things 'age', both with oil and various

elastomers. Rubbers dry out from ozone at a rate higher than oxygen, but that's still oxidation. In one of our factory

machines that has an 8KV corona wire humming along, all wire insulation, made from rubber or PVC, within about a

foot goes to heck in about 5 years and crumbles to dust. See ...

http://www.practicingoilanalysis.com/article_detail.asp?articleid=716&relatedbookgroup=OilAnalysis ... where there

is a demonstrable link between temperature and oxidation, i.e the wearing out of a lubricant. They say ... '

Calculating the expected life according to the so-called van’t Hoff´s Law also provides hints regarding the field

behavior of the lubricant. It states that the reaction speed of a chemical reaction changes with the temperature in

such a way that an increase in temperature of 10 K roughly doubles to quadruples the reaction speed. For example,

if a lubricant forms clear aging products after five days at 120°C, the same would take place after 10 days at 110°C,

after 20 days at 100°C, etc., and accordingly after only seven years at 30°C. Therefore, the lubricant has an

expected service life at room temperature (20 to 30°C) of approximately seven to 14 years. ' ... And so it goes. The

only way to exclude oxygen is to flood an impermeable container with nitrogen, and make sure it is hermetically

sealed. Every opening/closing of that container would need a new flood of nitrogen. We do this in our chem

processes here to retard oxidation of our various products. Properly done it vanquishes oxidation. This is rather

cumbersome for camera storage. But, from having dealt with too many old rangefinders, gunky lubricants will

happen. In my surmise a lot of gunk is due also to the inclusion of dirt and dust particles into the lubricant which

adds to it's viscosity. Yikes, enough already ! Jim M.

I think Jim is on to it. I have never heard of the lubricants in lens or cameras being water based, so humidity, at least low humidity shouldn't be an issue for a lens. Oxidation is the enemy as it temperature. I can't really expand upon what Jim said at all.

 

I guess I am mildly lucky, it can get pretty humid in central MD, but with central air conditioning my humidity level will sometimes go up to about 50% in the summer time inside and tends to over around 20-30% in the winter time. The only time it is higher is for those few weeks in fall and spring when no climate control is used in the windows are open most of the time, though even then if it is a really humid day I generally close up the windows and turn the AC or heat on low (if for no other reason then for comfort, I hate high humidity even if the temperatures are mild).

Guys, forgive me, but it seems to me these relative humidity percentages are awfully high when I was expecting low. I want to say that I

once read a book by a guy named Bruce Hoadley, Ph.D. in Timber Frame Engineering at Yale University, called "Understanding Wood."

Hoadley's book included some chapters on relative humidity and how it affects wood and plywood furniture.

 

I want to say that one of his assertions was that inside climate controlled/air conditioned environments, we were really

drying out our homes. So much so, that the average air conditioned home was actually worse for all-solid wood furniture

than a non-air conditioned home. I want to say that one of the things I learned from this is that there may actually be a

sound structural basis for choosing plywood laminates for longevity in air conditioned environments.

 

The thing that gets me is, Hoadley's text mentioned two points, if I recall right, that stick out here. One, seasonal

fluctuations in outdoor temperature and humidity did, affect indoor measurements. In one example, wintertime climate

controlled residences were testing out as dry as deserts! Two, that the big question about relative humidity

measurements was, relative to what?

 

Finally, I remember seeing maps in that book which were classifying humidity changes as normal between 5% to 11% in

the United States. Yet, as I read the texts above, y'all are listing much higher percentages as references.

 

Can you educate me a little bit on this? It seems to me that first of all, if you are in a climate controlled residence, you

are already dessicating the air (perspiration control in humans as a form of cooling). And, two, can you print up a quick

math formula that shows how you are measuring the relative humidity to begin with? Thanks.

 

I may just be confusing seasonal changes in relative humidity against other humidity differences. And also, if you are in

a climate controlled environment, why worry? It seems to me that humidity is a big player in decay when I am out in the

field, but relatively easy to control through normal housework at home. Please advise. Thanks.

Shouldn't your household or business air conditioner or heat pump be your first line of defense against rampant humidity-

caused decay? My guess is that if you have an air conditioner or heating in the building that you take your camera

equipment back to, shouldn't your stuff be okay?

 

Maybe, if you live in a really cold or really hot place, relative to the temperature and humidity indoors (blizzard outside,

warm inside or egg-frying heat wave outside, cool AC inside), once you get beyond that first hour or two of adjustment,

wouldn't your stuff level out and be alright?

So, if Sarah, OP, has got a hundred percent humidity indoors, wouldn't she just want an air conditioner? Seems to me that

she would be soaked in sweat all the time! If she's got electricity, then she need to sell some pictures and get an air

conditioner! Cool off, Sarah! Write back. Does it really feel that muggy inside your main photo equipment storage area?

Las Vegas! If OP lives in Las Vegas, I doubt she has anything to worry about. I'd bet that the biggest body of water out

there is in some fountain in the lobby of one of those expensive casino hotels! I would expect her to have the opposite

problem; humidity so low that it sucks every bit of moisture out of flexible weather seals, for example.

 

Now, if you were going white water rafting, scuba diving (fresh or ocean), moving through a swamp, bog, marsh, estuary,

beach or jungle, then I think you'd have to safeguard against humidity decay.

The biggest body of water "out there" is Lake Mead. However, that has little to do with the relative humidity in most of the greate Las Vegas area.

 

Here in NM, we can have humidity as low as 2% and as high as 100% (raining) - and during the "monsoon" season, it will start out at 35-40% in the early morning, go down to 8-12% during the day, and back up to 80% or higher for a brief period in the afternoon right after it rains. If you have a "swamp cooler" instead of air conditioning the interior of the house will generally be in the 60% RH range.

 

As to what humidity is "relative to" - that's very simple it's a calculation of the partial pressure of the water in the gas mixture to the saturated vapor pressure of water at the temperature of the mixture. This is why warm air is more humid than cold air - and explains why Antartica is considered a desert...there is no mystery as to what the definition of relative humidity may be.

 

I would guess Mr. Hoadley really didn't understand the term "relative humidity" if he actually made the statement, "... that the big question about relative humidity measurements was, relative to what?"

 

Relative humidity is not a measurement - it's a calculation.

Jim, THANKS for the useful information. What you say makes sense. It makes me want to avoid "hot box" solutions, and it makes me more confident in my sealed container solution.

 

Les, do you experience deterioration even in modern rubbers and plastics such as used in a modern camera? Also, do you think it could be due in part to the intense UV and high ozone in LV?

 

John, I don't live in Las Vegas. Les does. I just looked up the climate statistics. I live in Coastal Virginia. The problems occur when there is wet/rainy weather and when the temperature outside is in the high 60's to low 70's. The ONLY approach during days like those is to dehumidify. It can also be done by running the furnace, then running the AC, and then repeating and repeating. It can be done by running a dehumidifier, which is essentially the same approach. But do understand that it's quite comfortable inside, albeit rather sticky. There's not really a problem during the summer, as the AC condenses moisture. It's also not a problem during the winter, as the heat lowers the RH of the air. It's just a Spring and Fall thing.

 

Regarding the RH values: My figures are empirical. I measure RH using either an electronic hygrometer or (more commonly) humidity indicator cards I have stationed about. It sounds like the low values you quote are the intraday swings in RH, not the absolute values or even the seasonal swings. If there is any convention as to what constitutes "normal" humidity, it is 42% RH, established by the piano industry. (Pianos vary greatly in tuning, depending on the moisture content of the soundboard. Many pianos even have elaborate humidity control systems designed to maintain the RH within a 5% range of this central value.) This value (42%) is a "comfortable" humidity that exists commonly in homes that is healthfully moist and that doesn't introduce mold and mildew problems.

 

Regarding wood and furniture: Completely different thing from plastics, metals, and glass. Wood and other fibers absorb and disperse large amounts of moisture and expand and contract greatly accordingly. Wood expands and contracts across the grain, and not so much in the lengthwise direction, which wreaks havock on furniture if there are large humidity swings. (Think about the dimensional shifts, particularly where wood abutts into mortices.) None of this applies to camera equipment, apart from my collection of early 20th century and late 19th century cameras (made of wood).

 

I appreciate everyone's input on this matter. Thanks for taking the time to offer your thoughts! :-)

 

Peace,

Sarah

Modern plastics& rubbers are not immune to UV & ozone, just improved a fair amount. Compare nitrile, gum. EPDM and urethane rubber and see the range of resistance to oxidation. And. for those who have ever bought a new car and parked it in the summer sun, remember the smell ... and the eventual filmy glop that forms on the inside of the windows and windshield? Part of that odor and much of the window 'grime' is vinyl plasticizer exuding from the various plastics in the vehicle. It's added to keep the plastic supple and not degrade quickly under duress (think Armorall). Eventually the older car' start to show shrunken, chalky or crazed and cracking plastic surfaces, particularly those facing the sun ... like top of dashboards. And I'm 57 and starting to notice the same happening to me ! Jim M.

Have you asked this from the camera manufacturers themselves? They should at least know, they know what their products are made of.

 

Relative humidity where I live is usually a bit high, but the outside temperatures are rather cool to bonefreezing cold so the feeling indoors ranges from comfortable to dry.

Oskar, I have an email out to Zeiss but haven't heard anything. I haven't found the 30% claim anywhere else. I might pitch the question to Canon.

 

Jim, I remember parking a Cadillac in the summer sun in Las Vegas for a few months (but with a cover over it). When we moved the car, tread came off the tires (stuck to the pavement). The windshield had also cracked! That's a brutal place! ;-)

In terms of my measurement of relative hummidity, my thermostat for my central air unit calculates the RH. It is a new central HVAC unit (my old one died about a month ago to the tune of $5700, ouch). For the last month the relatively hummidity hovers between 40 and 50% depending on the temperature and hummidity outside. I also used to have a hygrometer, but I broke it about a year ago with a bookcase (knocked the bookcase over moving it and crunched a few things on my desk, fortunately not my monitor) For outdoor hummidity levels, I just check weather.com or another weather website for the current conditions in my area.

It might be that not that many people at Zeiss know fluent English, which might delay the answer. Please let us know if you get an answer. Probably doesn't hur to ask Canon too.