Best practices and construction for dust covers

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farnsy
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Best practices and construction for dust covers

#1 Post by farnsy » Mon Oct 11, 2021 5:35 am

I would like to up my dust-cover game. Right now my microscopes sit under one of the basic solutions you see a lot of: (1) the vinyl covers that tend to come with microscopes (2) the nylon fabric covers that sometimes come with microscopes (3) clear trash bags like are used in commercial applications. Of the three, the trash bags are actually my favorite for reasons I will describe below. However, none of these are really what I consider to be elegant. I can't look at my microscopes and feel like I've really worked out the best mix of protective, convenient, and attractive. For one, I'm not 100% certain what all the desirable features would be. I would be interested in feedback and ideas.

Some principles I have thought about

Dust covers should be somewhat form-fitting. A big problem with vinyl covers, and most fabric ones, is that they are stiff and large and leave a large air gap. Dust doesn't always move down, so the more air you have moving around, presumably the worse your protection. I also find it quite unsightly when dust covers are too big. The trash bags are softer and fit around my microscopes a little better, but I would hardly call them form-fitting nor elegant.

Dust covers should have some weight around the edges. Similar to the above concern, I would like a cover that had some kind of weight around the edges so it would pull down to the tabletop. I often find that my dust covers (especially vinyl) are crinkled in such a way that there is a big gap allowing air in and out because of the stiffness of the material combined with a lack of weight at the edges. Perhaps elastic or a string tie-off at the bottom could be an alternative.

Dust covers should be cheap and available in a few sizes. That's another reason to like trash bags. But I'm open to materials that are more expensive than trash bags.

Transparent is somewhat nice as it allows you to look at the scope. Although this should not matter, I find that I'm slightly more likely to spend time with my microscopes if I look at them as opposed to an opaque cover.

I'm not sure breathable matters. It's not clear to me that the air close to the microscope is more humid than outside in the room. A lot of times the opposite is true. Actually, I've thought about completely air-proof covers and then a bowl of silica water-absorbing crystals inside or something. Though where I live the climate is very inhospitable so we almost always have a huge A/C or heater drying the place out.

I'm not 100% confident in any fabric not producing some amount of dust. On a related note, I suppose plastic covers might off-gas, but I've never heard of someone complaining about effects from this.

Is there any advantage to double-layering? I have considered a tight interior dust-cover and then a larger one over it, but I'm not sure if there's any advantage.

Of course, any reasonable dust cover does the main job, but I'd like to optimize. And I'm interested in principles that I may not have thought of. I have had a few ideas too, and I'm interested in your thoughts.

Ideas I want input on

Clothes for microscopes. I've considered making really form-fitting covers for my microscopes that can be left on all the time. That is, they don't cover the eyepieces or impede working the mechanics of the scope. Obviously, this would probably require another cover over it when the scope is not in use. However, there are gaps in, for example, parts of my microscope head and I worry about dust getting in there over time, even while I'm using it. One idea for tailoring microscope clothes would be cloth and a sewing machine. I also suspect I could melt some seams into plastic bags using an iron.

Hard covers for the main stuff. I have 3D printed some eyepiece covers and covers for my illumination lens. Those are the places that really annoy me when they get even a tiny bit of dust on them. There are probably some other spots I could cover with hard plastic as well if I try. I was thinking of covering the hole in the stage to prevent dust from settling on the tip of my condenser.

Acrylic enclosure. This is a little extreme, but I've thought of building acrylic boxes to go over the microscopes that fit snugly on the tabletop. Then I would use a bowl of water-absorbing crystals to keep the humidity very low and a little inline filter with an aquarium pump to purge floating particles inside. This is a little less feasible with my most recent scopes, which are physically large. Still, kind of an interesting idea.

Rolled up rice bag or something that I can sew or attach to the bottom of the cover in order to keep the edges down.

What do you guys think? Have any thoughts about my ideas, or perhaps found thought of something even better? Have I missed any of the main principles governing optimal dust protection?
Last edited by farnsy on Mon Oct 11, 2021 5:42 am, edited 1 time in total.

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Re: Best practices and construction for dust covers

#2 Post by BramHuntingNematodes » Mon Oct 11, 2021 5:40 am

I have thought a big case with glass doors would be good, like what we had back in college.
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Hobbyst46
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Re: Best practices and construction for dust covers

#3 Post by Hobbyst46 » Mon Oct 11, 2021 6:18 am

If the microscopes are on constant display, the best would be to leave them uncovered in a dust free-space. A room can be made clean with slight over-pressure (relative to the ambient air pressure), or alternatively, sealed against draught.

Another alternative is simple "rectangular box" covers, sewn of heavy double-layer cotton cloth. A double layer of upholstery cotton cloth that we buy by the meter( yard). Cotton attracts less dust than synthetic fabrics do. Colorfully patterned cloth (flowers, geometric prints etc) makes a delightful display. And, perhaps contrary to intuition, does not release fibers, at least after initial washing. A double cloth layer will keep the cover sturdy enough, in the form of a vertical "box". And easy to remove when one wishes to actually use the microscope. Plastic bags sometimes smell and tend to retain humidity, which I find negative.

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Re: Best practices and construction for dust covers

#4 Post by PeteM » Mon Oct 11, 2021 6:54 am

I'm not sure these are best practices, but here's what I do.

The best scopes are in a library, which has a HEPA filter continuously running on law and a dehumidifer. The HEPA filter keeps dust down. The dehumidifier, set to around 55% relative humidity max, lessens the chance of fungus on optics.

Some scopes are in padded nylon cases. Some of the larger ones are stored in totes with lids - maybe not the best since these tend to be made out of PVC which can outgas (plus smell and be somewhat unhealthy). However, I haven't noticed any problems and they certainly keep dust out.

For covers I just use clear polyethylene (LDPE) bags. LDPE doesn't smell and outgasses significantly less than the PVC / vinyl covers sometimes supplied with microscopes. I've never felt a need for weighted edges - the polyethylene bags once pulled over a scope stay in place. Cotton fabric covers should also be fine, if periodically washed.

Originally, I bought heavier 4 and 6 mil bags in various form-fitting sizes - but am now gravitating to 2mil thicknesses even in large sizes. They do just as well keeping dust off, fit a bit better, and are cheap enough to pitch should they ever get seriously dusty on the outside. McMaster-Carr is one good source of open top bags of most any size. They even make especially low outgassing clear bags, still affordable, meant for clean room use.

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Re: Best practices and construction for dust covers

#5 Post by MicroBob » Mon Oct 11, 2021 7:17 am

Interesting topic!
Keeping the microscope clean and in good order is more important that details like the correction class of the objectives and cheaper to optimize. I don't have any real wonder solutions to offer though. I had a couple of cotton covers sewn from black and white cotton that look quite nice but are not high enough for my now more advanced microscopes. :oops: For the Phomi I have a PVC cover, old enough that it shouldn't give of much gas. If nothing else is available a cotton shopping bag without the loops works quite okay (wash before).

I like the idea of the hard covers for field aperture and eyepieces! The Idea with the close fitting cover seem not very pratical to me but I would love the look of a Sesame Street Grover - cover!

Some thoughts:

- A ridgid case may take up too much room when removed
- washing would be a simple method for the occasional cleaning
- Most dust comes from above, so a mini skirt cover that leaves a gap of 5cm already works quite well
- For curtains lead rope is available that would keep a cover down nicely
- In humid areas the cover could be vapor-proof and contain silica gel

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75RR
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Re: Best practices and construction for dust covers

#6 Post by 75RR » Tue Oct 12, 2021 1:54 pm

.
I am still using cotton pillow cases - one inside the other ... and yes they most likely could do with a wash about now!
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Re: Best practices and construction for dust covers

#7 Post by apochronaut » Tue Oct 12, 2021 2:34 pm

I just use very large 6 mil industrial poly bags like those used to vac pack large fish. They are about 30" long , so I trim them to an appropriate length. Punch a few holes near the top for some updraught. For very large microscopes with remote illuminators that are as long or longer than they are tall, there are versions of those bags with wider than tall dimensions. They are stiff enough to stand up by themselves. Pennies each.
I usually remove any fish, prior to use.
Last edited by apochronaut on Tue Oct 12, 2021 6:37 pm, edited 1 time in total.

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Re: Best practices and construction for dust covers

#8 Post by mete » Tue Oct 12, 2021 6:07 pm

Not with the microscopes yet but with many other electronic instruments, printers etc. that does not come with a dust cover, I use custom covers from this company: https://rotri.de/ . It writes they are polypropylene. I cant compare this with something else as I only use them or the original dust covers that comes with the products, but I am pretty happy with them.

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Re: Best practices and construction for dust covers

#9 Post by MicroBob » Tue Oct 12, 2021 7:02 pm

mete wrote:
Tue Oct 12, 2021 6:07 pm
Not with the microscopes yet but with many other electronic instruments, printers etc. that does not come with a dust cover, I use custom covers from this company: https://rotri.de/ . It writes they are polypropylene. I cant compare this with something else as I only use them or the original dust covers that comes with the products, but I am pretty happy with them.
Thank you for posting, a cheap and convenient way to a custom made cover!

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Re: Best practices and construction for dust covers

#10 Post by PeteM » Tue Oct 12, 2021 7:45 pm

mete wrote:
Tue Oct 12, 2021 6:07 pm
Not with the microscopes yet but with many other electronic instruments, printers etc. that does not come with a dust cover, I use custom covers from this company: https://rotri.de/ . It writes they are polypropylene. I cant compare this with something else as I only use them or the original dust covers that comes with the products, but I am pretty happy with them.
FWIW, polypropylene, like LDPE (low density polyethylene), is a relatively safe and low outgassing plastic compared to PVC and vinyl. I'd agree they should work well.

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Re: Best practices and construction for dust covers

#11 Post by enricosavazzi » Sun Oct 17, 2021 9:02 am

I have given some thought to the problem of covering my microscopes, but so far have not acted because we have been moving frequently the past few years, and did not want to increase the amount/volume of our stuff to pack and move. So far I made do with large (almost single-blanket size) blue pieces of nylon or rayon (a.k.a. synthetic silk) cloth, and in one case parachute cloth (lightweight but with rip-stop weaving). This works, but of course is far from "elegant". Now it looks like we will make our last move in one month or so, to a permanent accommodation.
For my BX50 in this permanent setting, which is too large and heavy to simply move to a cabinet, I have been thinking of a parallelepiped enclosure of rigid plastic panels (the lightweight type with hollow channels, sometimes used for outdoor enclosures and small greenhouses) kept together by modular aluminum profiles (20/20 should be enough). The front panel should be easily removed for normal use of the microscope. The whole enclosure should be lightweight enough to lift away for complete access to the whole microscope for maintenance and cleanup. Total size should be something like 80 by 80 by 80 cm.

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Re: Best practices and construction for dust covers

#12 Post by 75RR » Sun Oct 17, 2021 12:20 pm

.
They used to cover microscopes with glass domes - might be worth looking into

https://www.ebay.co.uk/itm/Large-Glass- ... 3861482909
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Re: Best practices and construction for dust covers

#13 Post by enricosavazzi » Sun Oct 17, 2021 3:48 pm

75RR wrote:
Sun Oct 17, 2021 12:20 pm
.
They used to cover microscopes with glass domes - might be worth looking into

https://www.ebay.co.uk/itm/Large-Glass- ... 3861482909
A glass dome would work for a small microscope, such as a teaching-level stereomic. A glass dome big enough to contain a large scope like a BX50 would be extremely expensive, and too heavy and fragile to lift safely.

An acrylic dome would be less fragile and lighter, assuming one can find this. Acrylic hemispheres are common, but elongated domes not so much. A box made from glued flat acrylic sheets (resembling an aquarium tank in shape and size, but not necessarily as thick as an aquarium tank) would work just as well as a dome, and most likely be cheaper. Polycarbonate domes are also available, and probably mechanically stronger, but less transparent than acrylic.
Last edited by enricosavazzi on Sun Oct 17, 2021 4:16 pm, edited 1 time in total.

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Re: Best practices and construction for dust covers

#14 Post by 75RR » Sun Oct 17, 2021 4:08 pm

.
You are probably right about the cost and weight of a glass dome large enough for a BX50, I have seen a more modest sized Zeiss GFL in one though.

Agree acrylic would be more practical. Would be nice to be able to see one's microscope when 'covered', though there is the extra space to consider versus a soft cover.

https://www.glass-domes.co.uk/acrylic_cases.htm
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Re: Best practices and construction for dust covers

#15 Post by DonSchaeffer » Mon Oct 18, 2021 8:04 am

I'm still using the dust cover that came with my scope. Is there anything especially wrong with them?

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Re: Best practices and construction for dust covers

#16 Post by dtsh » Thu Oct 21, 2021 9:01 pm

I have some poly-cotton blend covers I sewed for a few of my microscopes. They look niceer than plastic bags draped over, but I'm not sure they're any better.

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Re: Best practices and construction for dust covers

#17 Post by charlie g » Fri Oct 22, 2021 3:10 am

I suggest our battle with dust on our optics demands a repeated and compulsive shut-down protocol before we shroud our microscopes with dust covers.

A cheap rubber-bulb 'air puffer' should be used on the occulars, on the stage, on the substage optics..then cheap 7 oz plastic cups ( these also inner side air blasted before application on the occulars and other light-ports)...then these plastic cups are seated on the trinoc optics.


Only then do I shroud my stand with it's dust cover. My vinyl covers have brand name of the workhorse stand I enjoy...these stands are decades old..so I like their fashion on my bench.

Thanks for this practicle post by our OP! all he best, charlie g

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Re: Best practices and construction for dust covers

#18 Post by microcosmos » Fri Oct 22, 2021 3:55 pm

Like Charlie, I blow down the entire microscope after every use (all optics, connections, gaps, upwards-facing surfaces, vents), before retiring it for the night, although I am too lazy to cover the optics with cups (I leave the camera mounted on the trinoc all the time, detaching it only to transfer photos).

My instrument is one of those that are too heavy to move, and it is 75 cm tall with the vertical illuminator and the camera. I use this huge cardboard box (which I've shown elsewhere before), which (unlike a soft cover) doesn't touch the eyepieces or any part of the instrument:

Image

One fear I have of a soft cover is that when I lift it, I might pull the eyepieces out of their sockets and smash them on the floor, or the fabric might catch on some protruding part and cause damage (I'm paranoid).

I have a box of the perfect dimensions because it once contained the dry cabinet I bought for the microscope only to realise that I couldn't possibly lift the microscope into the cabinet!

There are two refillable calcium chloride damprid canisters inside to keep it dry (I'm in the tropics).

I cut out small grooves at the bottom of the back of the box to let the wires through.

I have since lined the whole box with plastic sheeting on the outside to make it less breathable so the damprid works better.

When I need to use the microscope, I simply lift the entire box and put it on the floor. I prefer the microscope to have no obstruction in any direction when in use so I can make adjustments/inspect the instrument from any direction, and also because it has a 100W lamp plus a 50W episcopic lamp that should be well-ventilated to prevent overheating.

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Re: Best practices and construction for dust covers

#19 Post by microcosmos » Fri Oct 22, 2021 4:02 pm

One other possible consideration for the plastic-based soft dust covers is whether they contain plasticizers to make them softer, which may leach out after some years and leave a greasy oily residue on anything it touches.

Many stamp collectors actually have this problem with their old albums whose plastic sleeves are made of a similar material. Some of them have melted almost to liquid. I think that takes a couple of decades and might depend on the climate but I won't really want that kind of material covering my microscope for any length of time.

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Re: Best practices and construction for dust covers

#20 Post by 75RR » Fri Oct 22, 2021 5:05 pm

microcosmos wrote:
Fri Oct 22, 2021 3:55 pm

There are two refillable calcium chloride damprid canisters inside to keep it dry (I'm in the tropics).

I cut out small grooves at the bottom of the back of the box to let the wires through.

I have since lined the whole box with plastic sheeting on the outside to make it less breathable so the damprid works better.
My worry would be that a partially sealed box would just drag moisture laden air in, it could also trap moisture inside once the canisters are saturated.

I will stick to my double layered cotton pillow-case, that way one prevents dust and since the material breathes, it avoids condensation.

Note: Any cotton fibers that may land on a lens are easily removed with a blower.
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Re: Best practices and construction for dust covers

#21 Post by microcosmos » Sat Oct 23, 2021 2:39 am

75RR wrote:
Fri Oct 22, 2021 5:05 pm
microcosmos wrote:
Fri Oct 22, 2021 3:55 pm

There are two refillable calcium chloride damprid canisters inside to keep it dry (I'm in the tropics).

I cut out small grooves at the bottom of the back of the box to let the wires through.

I have since lined the whole box with plastic sheeting on the outside to make it less breathable so the damprid works better.
My worry would be that a partially sealed box would just drag moisture laden air in, it could also trap moisture inside once the canisters are saturated.

I will stick to my double layered cotton pillow-case, that way one prevents dust and since the material breathes, it avoids condensation.

Note: Any cotton fibers that may land on a lens are easily removed with a blower.
Thanks for your comments. I think the points you raised are important considerations, especially if the instrument is in a temperate/cold climate where there are big humidity/temperature gradients between night and day, especially if indoor heating is turned off for the night.

In my tropical case, the temperature in my non-air-conditioned lab is constantly high and relatively uniform (day and night) and the humidity is always high outside the box, so having a breathable cover will not work well as it lets in the humidity (with or without the damprid) - unless there's a technology that lets air permeate in both directions while letting water vapour out but not in? Does Gore-Tex do this?

The box is almost completely sealed - there are no openings at all, with just a little leakage along the line of contact between the box and the table surface, so the damprid is able to do its job.

However, as you mentioned, I have to monitor the damprid to ensure it doesn't get over-saturated. But I think calcium chloride is much safer than silica gel in this respect. From what I've read, calcium chloride can absorb much larger amounts of water and holds on to it, while silica gel absorbs much less and its action degrades rapidly as it accumulates water and there's a much greater danger of unknowingly leaving it to a point when it starts releasing the water back out again.

[edit: just a technical correction that I believe silica gel adsorbs, not absorbs.]

Talking about cotton fibers landing on the scope, is there some sort of lint-free fabric that's breathable and doesn't shed fibres and doesn't generate static? Besides lenses, would the fibers not cause problems on other parts of the scope as well, such as greased mechanisms where the fibers could get stuck on the grease and accumulate over time, or even just gaps where fibers could fall in and eventually find their way into the tube or into the focusing mechanism etc.? Maybe this isn't a significant problem since many people use cotton covers with no apparent issues.
Last edited by microcosmos on Sat Oct 23, 2021 4:55 am, edited 1 time in total.

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Re: Best practices and construction for dust covers

#22 Post by farnsy » Sat Oct 23, 2021 4:15 am

microcosmos wrote:
Sat Oct 23, 2021 2:39 am
But I think calcium chloride is much safer than silica gel in this respect. From what I've read, calcium chloride can absorb much larger amounts of water and holds on to it, while silica gel absorbs much less and its action degrades rapidly as it accumulates water and there's a much greater danger of unknowingly leaving it to a point when it starts releasing the water back out again.
This is new information to me, and very interesting. I have a hygrometer in my room and it's always between 45 and 50, day or night, winter or summer. That's not nearly as high as other people have, but I am paranoid about something bad happening to my scopes. I might have to get a little more serious about handling humidity.
microcosmos wrote:
Sat Oct 23, 2021 2:39 am
Talking about cotton fibers landing on the scope, is there some sort of lint-free fabric that's breathable and doesn't shed fibres and doesn't generate static? Besides lenses, would the fibers not cause problems on other parts of the scope as well, such as greased mechanisms where the fibers could get stuck on the grease and accumulate over time, or even just gaps where fibers could fall in and eventually find their way into the tube or into the focusing mechanism etc.? Maybe this isn't a significant problem since many people use cotton covers with no apparent issues.
I am way too paranoid to allow cotton on my microscopes. It seems like it would both shed fibers and attract dust from the air or whatever surface it is placed on. One of my scopes came with a fabric cover but it's a tight weave synthetic of some kind--crinkly and shiny. I've been wondering myself about whether this is the best material--and exactly what material it is. I do like my clear polyethylene trash bags, but I could be persuaded if there is something better. Polyethylene does offgas, apparently, but much more lightly than PVC or polystyrene. I can't smell it no matter how close I get. Still, my paranoia is strong.

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Re: Best practices and construction for dust covers

#23 Post by PeteM » Sat Oct 23, 2021 5:47 am

Perhaps worth reiterating that a HEPA air filter can work wonders in limiting dust. Decent ones are around $100, use relatively little electricity, and could run 24/7 on a whisper-quiet low fan setting.

If scopes are in a closed room, a small dehumidifier set to turn on and off with a humidistat can keep the relative humidity below 50% - usually enough to keep fungus from forming.

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Re: Best practices and construction for dust covers

#24 Post by MicroBob » Sat Oct 23, 2021 6:33 am

In my experience and under our conditions fungus problems only start to occur when humidity is clearly above 60% for long periods of time. For the tropics a dehumidified based on a Peltier element might work. I once bought one to dry out our little used car in winter time but it didn't work where a bigger compressor based dehumidifyer does work. But in a warm room it should be able to keep a microscope box dry.

I ordered and received 3 dust covers from the company mete recommended: https://rotri.de/
I haven't tested them for fibre pollution yet but they fit nicely and I didn't have to do more than to measure, decide and order. The material feels like some kind of thin plastic felt, reinforced by spot weld points. It doesn't look especially valuable but does it's job. The seams are sewn nicely and a label is added in one seam. The web configurator is really great and so one can easily order covers of not so simle shapes. The material is a bit stiff, not like fabric and the covers pull of like a wet carboard box, semi stable. Since I wouldn't have come around to replace my old miniskirt covers soon I'm very happy about them.

The day after I ordered them a heap of fine black fabric fell into my hands - what does this say to me??? :lol:

Bob

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Re: Best practices and construction for dust covers

#25 Post by microcosmos » Sat Oct 23, 2021 6:41 am

PeteM wrote:
Sat Oct 23, 2021 5:47 am
Perhaps worth reiterating that a HEPA air filter can work wonders in limiting dust. Decent ones are around $100, use relatively little electricity, and could run 24/7 on a whisper-quiet low fan setting.

If scopes are in a closed room, a small dehumidifier set to turn on and off with a humidistat can keep the relative humidity below 50% - usually enough to keep fungus from forming.
I wish I could do something like this actually. The problem I have is that it would require the windows and doors to be closed, which in my tropical climate means installing and running air-conditioning which is costly (even if used only when using the microscope) and which I feel creates unnecessary environmental impact for a country where the outside air temperature is just right for living. But it works if you’re already using aircon.

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Re: Best practices and construction for dust covers

#26 Post by microcosmos » Sat Oct 23, 2021 7:01 am

MicroBob wrote:
Sat Oct 23, 2021 6:33 am
For the tropics a dehumidified based on a Peltier element might work. I once bought one to dry out our little used car in winter time but it didn't work where a bigger compressor based dehumidifyer does work. But in a warm room it should be able to keep a microscope box dry.
If this Peltier device is what’s installed in my dry cabinets, I can say it works really well in a microscope-sized airtight space that is not opened too often/too long. Completely silent, no moving parts and uses very little electricity.

It’s tricky to have one on my cardboard box because every time I use the microscope the entire system is vented to the outside air so the Peltier device would be subject to quite high workloads on an almost daily basis as it has to re-dry the entire box every time. I had one that failed after a few years and I think it can’t really handle heavy workloads long-term.

But nor do I really like having to monitor and refill calcium chloride flakes!

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Re: Best practices and construction for dust covers

#27 Post by 75RR » Sat Oct 23, 2021 6:11 pm

microcosmos wrote:
Sat Oct 23, 2021 7:01 am
But nor do I really like having to monitor and refill calcium chloride flakes!
Was reading up on homemade dehumidifier boxes and someone said they channeled the heat from their UPS (which is always on) into the box.

Might be worth looking into especially if you have a way to measure internal and external humidity.
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Re: Best practices and construction for dust covers

#28 Post by PeteM » Sat Oct 23, 2021 6:44 pm

Perhaps someone here will know more about the conditions under which fungi/mold grow?

With respect to mold, here's a bit from our EPA suggesting below 60% and ideally 30-50%: https://www.epa.gov/mold/mold-course-chapter-2

What I don't know is the difference in growth between relative humidity over 50-60% and actual condensation below the dew point (warm moisture-laden air hitting a colder surface). This is a common problem with shops where the heat is turned off during the night and the doors opened in the morning. Warm moisture-laden air condenses on tools, causing rust.

I'd assume condensation would be worse for optics and mold growth as well -- and in that case using some small source of heat (UPS, power supply, incandescent bulb, tiny heater) in a small box containing the microscope would be somewhat effective protection (by keeping the moisture from condensing on lens surfaces).

On the other hand, if it's relative humidity pure and simple that fungi need for growth, then some sort of desiccant or dehumidifier is needed. We've sort of covered silica gel and calcium chloride. Compressor-type dehumidifiers can be relatively efficient, but cost around $300 up. The Peltier type Bob mentions (using the cool junction to condense out water) are simple and cheap. While not efficient, not much power would be required to keep a reasonably tight microscope box dry. Ideally, they'd be fitted with a humidistat - though few seem to want to spend the extra $20 or so that might add to the cost.

One thing I have learned is that most inexpensive relative humidity meters -- whether the old analog ones or the newer digital ones -- can't be trusted for accurate readings. At one point I bought half dozen of them to compare and contrast. A couple were way off. Most disagreed with one another and a sling psychrometer by +/- 5% (despite claiming better). One can use salt solutions to calibrate these, but even then they might drift. In my case, the humidistat on an otherwise OK dehumidifier reads around 60% when the actual room is around 45-50%.

Another thing I've learned is that many of the reasonably priced objectives and microscope heads that come to me from various humid Asian locations, arrive with fungus on internal surfaces. A few I've managed to clean if there hasn't been too much damage to coatings and I can get access to every lens surface. It's always with some trepidation, though, that I then start using them near other optics.

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75RR
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Re: Best practices and construction for dust covers

#29 Post by 75RR » Sat Oct 23, 2021 7:49 pm

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This is what the Zeiss 'The Clean Microscope' booklet (see page 10) has to say:

https://www.zeiss.com/content/dam/Micro ... -zeiss.pdf
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Hobbyst46
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Re: Best practices and construction for dust covers

#30 Post by Hobbyst46 » Sat Oct 23, 2021 8:04 pm

A few comments about the above.
1. Gore-Tex allows passage of water vapour (e.g. human sweat) although it stops liquid drops. So it does not dehumidify.
2. Calcium chloride and silica-gel work more or less similarly - they adsorb moisture at room temperature and release it at high temperature. Water-saturated silica-gel can be dried (that is, renewed) by spreading it as a thin layer in an oven at ~200C, within an hour. Calcium chloride an be similarly renewed but I do not remember the temperature and time.
3. Silica gel is more hazardous than calcium chloride if it contains very fine (micron-sized) particles that might be carcinogenic. Calcium chloride is not - although it is hazardous, being an irritant.
4. Both calcium chloride and silica gel adsorb water fairly rapidly in humid climates. They are practical dehydrating agents only if contained within tightly closed spaces. That is, the microscope should be enclosed within an air-tight vessel/box/sack.
5. Plastic surfaces attract dust much more than do natural fiber textiles, because of electrostatic attraction. So, charlie g's idea of covering the eyepieces individually seems very good.
6. My microscopes are covered with double-layer sewn cotton covers. Once washed (once a year), they only shed very few fibers, which are easily removed as 75RR mentioned. And they were never a problem on the mechanical parts of my microscopes, in spite of their many metal surfaces and knobs and racks etc.
7. Most relative humidity meters are inaccurate as mentioned by PeteM. Especially at rel.hum.>80%. And calibration is an awkward process if done at home.
8. To prevent mold, I believe that the idea is to prevent condensation on the microscope. Even if the relative humidity is high, the fungus proliferate from liquid water, not vapors (please correct if that's wrong!). As long as the microscopes are slightly warmer (by very few degrees C) than the space in which they are enclosed, condensation will not happen.

I think that, if indeed condensation is likely (for any climatic/environmental reason), keeping the microscopes warm is the most practical and economical way. Less nuisance than dehumidifiers of any sort. HEPA filters are an overkill, IMHO.

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