Minimum humidity

<p>Hi all. A less abstract question from me for once. I know this was discussed on the forum a very long time ago

(with no obvious conclusion), but I thought I'd see if anyone had more recent news...<br />

<br />

I've had a few Nikon lenses flagged up when I tried to trade them in as having mould growing in them. The study

in which I keep my camera kit (when it's not cluttering my living room) is next to my bathroom, so my suspicion

was that in combination with general British conditions, it was getting a bit damp in there. Yes, I should get

everything out and shoot with it more, but absent time for that I got a small dehumidifier for the room.<br />

<br />

Since the dehumidifier has been running, various bits of rubber in my study have fallen apart (the grip from my

telescope focus knob, some bits of the handles on my shelves) and I've noticed the leatherette on my Pentax 645

peeling. I'd not noticed a problem with my Nikon gear until I recently attempted to get at the 10-pin connector

on my D810 and the rubber cover snapped as I was opening it (without me applying any significant force). I'm

suspicious that the low humidity - which can't be lower than the 30s, although I do have a chemical dessicant

dehumidifier in the cupboard that may be lowering the humidity more near itself - is causing brittleness and

shrinkage.<br />

<br />

Various Nikon manuals talk about a maximum humidity, with IIRC the figure of 45% mentioned somewhere. I've never

seen a mention of minimum humidity, and Nikon UK claim there's no such thing. I largely trust the lubricants to

be okay, but over an extended period I'm a little less sure about rubber and some glues.<br />

<br />

Does anyone have any reports on this, or advice on a lower limit for long term storage? I'm trying to walk the

line between mould growth and hurting something. Otherwise I'll just report back when the next part breaks!<br />

<br />

Thanks in advance.</p>

<p>I will let the forum chemists refer to the effects of low RH on materials, but I can talk about humidity levels. Until it gets cold outdoors, it is difficult to remove "too" much humidity with a refrigerator type dehumidifier. The dewpoint at the coil can't get below 0C without icing the coil. Most cooling coils operate to achieve an air discharge temp around 11.5C, which in a 22C room would result in about 48%RH. I doubt that your desiccant gets a large room significantly lower. Indoor RH levels between 40-55% are best to minimize mold growth.</p>

<p>Static electricity buildup is prevalent during low RH levels that occur when outdoor conditions are well below freezing and indoor temps are warm. Static discharge can damage electronics, but I am not sure about low RH effect on materials. Probably ozone and air pollutants do more damage to rubber type materials than low RH.</p>

<p>Thanks, Robert. I'd originally aimed at somewhere between 35-40% RH according to the settings on my dehumidifier (which I think is, indeed, refrigerant type - unless it's got a big peltier element in there). The little dessicant block won't do much to the room, but might lower the interior of the cupboard it's sitting in; it's there mostly for when the other one fills up and I forget to change it, or for when I put something away in the cupboard while it's still damp. It took a very long time to stop filling up every night, but it seems to be getting there, so I assume it's pulled a lot of water out of my books... It's not a large room, but it's possible the window is open a crack (I can't actually get at it to check), so it's probably fighting the atmosphere. Anyway, if it's safe to do so from a mould perspective, I'll aim at perhaps 45% rather than lower - both for the longevity of my kit and for power saving. The room's probably a little cooler than 22°C, especially when I'm not home, but hopefully not enough to change the equations. It's not a rain forest, although I'll be glad when the extractor fan in my bathroom is fixed rather than the current winter-unfriendly open window approach.<br />

<br />

The selection of things falling apart in my study could be coincidence rather than dessication, I just wanted to be paranoid. Especially when my 10-pin connector broke off! Fortunately I get the camera back tomorrow, hopefully with this fixed.</p>

<p>Does your dehumidifier add some ozone, while taking away some moisture? Saw that Robert pointed this possibility too.<br>

So far I have lost only two Nikon circ pol filters due to improper storage. Some fogged lenses I have been able to restorate. I had earlier some adhesive tape material inside of my camera bag. Obviously it was giving out material (gas?) that caused problems in the form of fogged glass surfaces. <br>

A small uv-light may be effective against mold.</p>

<p>Here in the high deserts of Utah the local humidity is naturally very low, particularly in winter. (We not infrequently see single-digit RH.) I have not noticed any significant deterioration of plastic/rubber parts compared to the 30+ years I lived in coastal Southern California, so I doubt that low humidity on its own is the culprit. If the parts were exposed to sunlight, then UV would be suspect, but clearly that is not the case. Added ozone becomes a possibility, particularly if your dehumidifier includes an electric motor (which it should). You might also investigate alternative sources of ozone in your home, including the lighting and other electrical equipment. See primers on the effects of ozone on rubber and other polymers <a href="http://www.applerubber.com/hot-topics-for-engineers/understanding-the-link-between-ozone-and-rubber-deterioration/"><HERE></a> and <a href="http://cool.conservation-us.org/waac/wn/wn07/wn07-3/wn07-302.html"><HERE></a>. There is also research indicating that ozone can react with certain materials to form even more harmful or corrosive materials, such as formic and other acids. Concentrations of these materials can build up in interior spaces if there is insufficient fresh air exchange. </p>

<p>Kari: I don't think so (I can't see why it would - there's a small motor, but...), but I guess I can't rule that out. I'm sure there are pollutants (not just cat hair) in my house, given my proximity to Heathrow and the consequent sunsets, but it seemed odd that I saw several things fail within a month of using the dehumidifier. But it could be that I saw one thing fail coincidentally and it made me notice the others. Good thought on the UV, though - I'll see whether I can zap things. My mould issues only reduced the lens value (because they needed internal cleaning), they weren't catastrophic - but I'd like to keep it under control.<br />

<br />

David: I figured there might be someone out there living in negligible humidity. (I've had grips come loose on my D700 and D810 in Australia and, I suspect, at Horseshoe Bend, I think because the heat softened the glue, but that's a different problem.) I'll try checking out the ozone situation, though I'd kind of expect to smell it. It <i>is</i> a fairly enclosed space, give or take any air that can get under the door. Thanks for the links; I'll stop blaming the humidity, if not the cause of it!</p>

<p>Andrew: Plastic generally has a very high coefficient of thermal expansion, so friction-fit items tend to be sensitive to heat. Plastics/rubbers typically have very low absorption of water, but can be sensitive to a variety of chemical and environmental factors, such as UV, ozone, etc. My work routinely requires that we evaluate the potential for interaction between various materials, and the chemical compatibility of plastics, rubbers, sealants, and the like is an ongoing issue. In regards ozone sources, any electrical appliance that generates a spark (such as motor brushes) can generate ozone. The concentrations need not be high enough for you to smell before they will be deleterious to sensitive materials. The same can be true of other chemicals as well. It can be a very fine line in trying to balance correct humidity with the need for fresh air ventilation. I have also found that a rapid change in humidity has unintended consequences. The wooden tiki I brought back from Hawaii cracked within three weeks of my return. Best wishes sorting it all out. </p>

<p>Thanks, David! I'll keep investigating. I'll see whether I can identify that ozone is definitely the problem - the UV lamp solution to lowering ozone levels feels like it's going to offset my cunning plan of having a low-energy dehumidifier, so I'll have to investigate further. I have to say that lack of humidity being responsible for rubber perishing seemed a bit weird to me, although I was more willing to believe it of the glue on my Pentax coming unstuck. I'm reasonably confident of the cause of the grip moving on my D810, since I've read the instructions on how to replace the material, and it involves a heat gun. :-)</p>

<p>My intention was to use UV against the mold, not to combat the ozone ;-)</p>

Does UV lower ozone levels? I thought UVb was

partially ionising and encouraged the production of

Ozone from atmospheric oxygen. I may be wrong.

 

I'm also subject to the vagaries of British weather,

and the only time I've suffered lens fungus was

when my lenses/cameras were stored in leather

cases. Got rid of the leather, and no more fungus. Touch Vinyl!

<p>I live in the northern reaches of the Gulf Coastal Plain and humidity, especially in the summers, is not far off the actual coast (I think 100% humidity is still generally the maximum).<br>

Many of my film images are beginning to show biological (floral, mostly) effects. I keep them, but really rely on digital files for real archive. Digital can be archived, but you have to keep at it, just as you do with film.</p>

<p>Cameras, lenses and gear?<br>

Keep things like leather and cloth cases away from the hardware. Provide good circulation in the storage area, Use "dehumidification" (but I have no solution to the deterioration of 'rubber' etc). I suppose that large quantities of silica gel (<a href="https://en.wikipedia.org/wiki/Silica_gel">link</a>), regularly 'freshened' might be a path.<br>

If you want to scare any photographer with a collection of lenses, consult http://www.photo.net/classic-cameras-forum/00bbMF </p>

<p>Also use standard hygienics-- the spores are dispersed by the mildew, whatever, so isolate infected equipment and materials.<br /> Or burn them (bring out your dead)</p>

<p>I've lived in Las Vegas, NV for 16 years and haven't seen anything resembling the problem you describe. Equipment stored indoors seems to fare about the same as my gear did when I lived in the southeastern US (Tennessee and Alabama) for 20 years. So, having lived in single digit relative humidity for a while, I see no reason to suspect that dry air is the culprit.</p>

<p>I did live (never mind how long ago) in Florida with its high humidity, and learned that higher humidity associated with the sea shore means that the water vapor in the air has a higher salt content than inland air. How close to the coast do you live? The uncertainty of this idea is that if salt content is the problem, then it should be happening to everyone in your area. That should be easy to check.</p>

<p>RJ: I think I read some kinds of UV cause the ozone to break down? I need to do more research.<br />

<br />

JDM: Maybe I shouldn't keep some of my lenses in their cases; I'm trying to keep the cases slightly open for humidity and airflow reasons, but I keep several lenses in cases so that they're easier to stack and protected if I knock them out of the cupboard. At least I'm now rid of my 500mm f/4 with its big leather lens hood! And no, sorry, I'm not taking a blowtorch to my lenses. At least deliberately; if my older lithium batteries go up it's always possible I'll have an embarrassment.<br />

<br />

Bob: Thanks for the feedback. I'd be surprised if it's salt (I'm about 40 miles inland, I think). Other crud in the air is far from unlikely, though!</p>

"Hard" UV B/C bulbs are used in commercial sterilising cabinets for their biocidal

properties - used by hairdressers for example to

sterilise materials that would be damaged by

conventional chemical or autoclave sterilisation.

 

OTOH, short-wavelength UV is also an effective destroyer of the simple cells of moulds and fungi. So UV may well be beneficial in preventing lens fungus (although unfortunately its penetration through glass is poor once fungus has found its way into a lens). However, there's no doubt that UV can also degrade many polymers, including rubbers and plastics. On balance I'd keep deliberate UV sources away from modern photographic equipment, and seek other methods of controlling fungal spores.

<p>Fresh air and bright light are the cheapest preventatives for internal lens fungus growth. Store them in a place where air circulates-not in cases, bags, pouches, or any kind of closed storage.<br>

I also suspect chemical attack, because your humidity highs and lows are well within normal bounds.</p>

 

<p>Thanks again, everyone. I'll take things out of the bags and contemplate leaving cupboard doors open - although I was trying to avoid dust ingress that way. I'll look into an air filter to complement the dehumidifier.<br />

<br />

Speaking of burning lenses, I looked at a light through my 135 f/2.8 AI last night. It could probably cure staphylococcus. (It's been sharing the TC-16A - which itself looks okay - with the 500mm f/4, which I know was a bit mouldy.) The mount is a bit manky, too - I scraped quite a bit of gunk off the metal with a thumb nail. It's a shame - I was considering taking it with me to a wedding this weekend, and I'm still waiting for Nikon or Sigma to make a decent modern 135mm prime (somehow the Laowa 105mm manages not to have <i>very</i> nice bokeh despite having an apodisation element, and it's a bit short). Given the cost of the Nikkor, I'm guessing it's not worth a CLA. I'll not put it next to anything expensive, anyway (and I might leave a dessicant sachet inside the rear lens cap). Fortunately my 200 f/2 looks vaguely okay - that's the one I was worried about.</p>

<p>Follow-up... I'm wondering whether to keep shooting with my 135mm f/2.8 (not that it gets that much use, but sometimes even <i>I</i> want a small lens) or whether to start looking closely at the Samyang 135mm f/2...</p>