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04-09-2019, 03:43 AM   #16
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Undoubtedly correct!

It's certainly a fun topic to consider! I might actually branch this off onto a separate thread.

There are a couple of problems in biology in trying to assess absolute risk of infection. My background is in biochemistry, so I have some experience (emphasis on "some" - I'm specifically not a microbiologist - while I done microbiology, the focus was on immunology - so my interactions with microbes always involved the human body).

The moral of trying to assess risk in a biological system is that biological systems are big and complex - and chock-full of confounding variables that tend to be hidden away at the microscopic level.

TL;DR (sorry! This ended up being WAY longer than I thought!): there are so many confounding variables, and the spore density in the air is already so high, that introducing a reservoir of viable spores near to a lens may not actually have a noticeable effect on cross contamination rates (unless the reservoir is extremely active) - the limiting factor seems to be the resources available for spores within the lens, rather than the number of spores it is exposed to (as increasing the number of spores just allows them to use up those resources faster)


In other words - the resources (particularly water) available in a lens has a much greater effect on contamination rates than the spore loading.

It is rather like comparing the risk of driving on a gravel roads vs not driving on gravel roads... in a warzone. Sure, driving on a gravel road may wear out your car quicker - but that's probably not what's going to destroy your car.

In this case, water in the lens almost guarantees contamination - while having a contaminated lens nearby only slightly increase the risk - BUT a small risk over a long time is still a greater risk overall!


IT ultimately comes down to relativity of risk - you can follow my logic right down at the bottom of the post




And now the rambling begins!

So, as an example of my thought process - emphasis on the "my" part, I'm not a terribly great authority on the matter, if we wanted to try to quantitatively analyse the risk associated with cross contamination from one lens to another - what we'd do is we'd sample the lenses and their storage containers and cultivate the samples under controlled conditions.

The idea here is that we count the number of viable cells, and it's fairly easy to do this - you take your sample, serially dilute it (say, 1-in-10, 1-in-100, 1-in-100, for example) and culture each one. You then culture them and count how many colonies form - because we don't know the initial fungal load, we've diluted it so we'll always get one that doesn't just turn into one giant fungal colony.

Either way, once you get a suitably dilute sample and culture it, it's just a matter of counting the number of discrete colonies in a given area, and then working back by your dilution factor to work out how many "Colony-Forming Units" are present - which is just the number of viable cells in the original sample

Why yes, when I last done this, I had to do it by hand. There were a few hundred colonies. It was torture fun!

Anyway - so from here we can work out how many viable cells were present in our original samples - and these numbers tend to be quite large - for instance, a cubic meter of air typically contains several thousand viable spores - more on a hot day, less on a cold day.

So, where my thinking lies is in the sheer number of spores available to start a colony: because lenses are not optimal conditions, they act as a limiting factor - it's like rushing through the grocery store - no matter how fast you shop, you will always get slowed down by the queue at the checkout - it effectively establishes a minimum rate that you can pass through the grocery store.

In the case of lenses, my thinking was that given the limited surface area available, and the terrible sub-optimal growth conditions, you would reach a point where increasing the number of spores doesn't have a noticeable effect on the infection rate under those conditions.

In terms of risk, however, there are a ton of confounding variables - some fungi can't coexist (one will poison the other) - while others will coexist (one will make conditions better for the other) - and they often, but not always, like to partner up with certain bacteria in a mutual or commensal relationship. We also have all the chemistry (hopefully mostfully inert) going on in and on camera lenses, such as UV degradation of the plastics which can release various chemicals that both promote and retard growth - oils and lubricants might be digestible - and of course, we have the actual geometry of the camera lenses - some hold water better - some present a larger surface area for fungi to enter - others wick moisture (and fungal spores!) inside them while others are harder to get into than a nun's lockbox. Not a euphemism by the way - I once broke into the lockbox of a nun.

Why are they looking at me like that? They lost the key and asked me to break into it for them to retrieve their prized belongings! Sheesh - what were you thinking of?

The final "big" variable I can think of is the reproduction rate of the fungus: which ultimately comes down to how often it produces spores (sexual or asexually... and sometimes parasexually... fungi alternate between them depending on conditions - kinda - sometimes - often - but not always. "It's complex" - a phrase that describes most of biology ).

Put simply - a fungus (or any organism, for that matter) can only reproduce at a certain rate, limited by their environment, and this results in boom-and-bust mechanics - when conditions are great they reproduce as fast as they can until they use up all their resources. As far as I know, all organisms do this - humans included. I look forward to the "bust" phase when our technological prowess doesn't allow us to extract enough resources any more.... but anyway, our fungus' biggest limiting factor in its reproduction rate is water (and food (and temperature)). Water is the big one in lenses though.

The best way to look at this is with an hypothetical example:

Let us suppose we have two lenses: one has had acute water exposure - you dropped it in a puddle *twitch*. The other has chronic water exposure - you live in the rainforest *also twitch*.

You deliberately introduce a fungus to both lenses and let it reproduce. "Woo!" it says as it spreads as fast as it can, producing fruiting bodies periodically along the way.

The acute-exposure fungus reproduces to fill its niche, and before long has ran out of water. The number of spores it was able to produce in that time is proportional to the amount of water present - and once the fungus dies, its spores remain - so we have a specific spore load on this lens.

The chronic-exposure fungus does the same - but because there isn't a massive pool of water available, it reproduces slowly, at a rate governed by how much water it can extract from the air (or by the rate at which water condenses out of the air and onto the lens) - it will produce spores and expand again, but not being limited by water, it's niche is instead limited by the available food source. Food is necessarily limited in a lens (though that isn't to say there isn't more than enough food for the fungus to ruin your lens!) - so it too will eventually die out, leaving a specific spore load.

This allows us to differentiate between a "live" lens (producing spores) and a "dead" lens (produced a certain number of spores but can no longer do so).

In both cases, we deliberately introduced the fungus to the lens and let it consume its available resources - I suspect the chronic exposure lens to be the worst off (it may be decades before it exhausts its food sources, depending on the lens!)

The main point is that we have a reservoir of spores in these lenses - BUT - remember our confounding variables on how easy it was for a given spore to infect a lens? The lens geometry and whatnot? Well - this is where things get interesting! Because those same confounding variables now apply in the spores getting back out of the reservoir!

In other words, we have another rate-limiting factor!

There is one final, and interesting point - spores don't stay in one place. If I put a pile spores on your desk, entropy will do its best to spread them evenly through the room (though they have a propensity for sticking to surfaces - so the surfaces will often have a higher density of fungi than the air). This means that the concentration of spores at any given time falls off with distance from your pile of desk spores - and will slowly rise until the spores are as evenly distributed as they can be.

The same would apply to lenses - if a lens is full of spores, the spore concentration will (slowly) fall off until it is in equilibrium with the environment - if I put it in a bag with lenses - then depending on how often you open and close or ventilate the bag, the total number of available spores in the bag will slowly decrease to the equilibrium point with the outside environment - HOWEVER - it is important to note that there may not be a great difference, depending on how many spores the individual lens was actually able to produce, and how quickly it can disgorge them into the environment. You may find that even if a lens has 1000 spores in it, it might only be able to release one per hour into your bag - which loses 1 per hour itself - in which case the spore concentration in the bag itself will only fluctuate a little.





Ultimately it all comes down to a great big, multiphase equilibrium that is best described in a number of short premises:

Premise 1:
  • Any given environment will have a spore load.
    • The spore load is the number of spores in a given area.
      • The load is governed by the equilibrium of spore gain to spore loss.
        • Gain/loss is controlled by external factors:
          • High humidity increases load
          • High airflow increases the rate of change
            • (it can increase or decrease the rate of gain or loss)
      • The magnitude of the load is limited by resources:
        • An environment cannot support more than its resources allow.
          • Fungal mass is limited by:
            • The mass of available water
            • The mass of available respiratory gas
          • Fungal growth rates are limited by:
            • The rate of availability of water
            • The rate of availability of respiratory gas
        • Fungi (and all organisms) follow boom and bust mechanics:
          • Thus a given population of fungus will:
            • Expand and sequester all available resources
            • Suffer a die off
            • Continue to grow at a rate determined by the rate of availability of water and respiratory gas

Premise 2:
  • All environments dealt with in this example exist, in equilibrium, within a larger environment.
    • Your camera lens environment is in a camera bag environment
      • Your bag environment is in a house environment
        • Your house is in a local environment
          • etcetera, etcetera.

Premise 3:
  • Following from Premises 1 and 2:
    • A fungal load exists at every level
      • Every level is in equilibrium with the levels above and below it
        • Changes to that equilibrium at one level will affect all other levels
          • Changes at higher levels affect lower levels more severely than the inverse.
            • This is due to scale: smaller levels have a lower volume, with fewer resources available, and vice versa.
              • For example, if I filled your neighbourhood with helium everybody's voice would be squeaky: conversely, if I filled your house with helium only people in your house will be squeaky. Finally, if I filled a small box in your house with helium, nobody would notice.
                • Please do not do fill your town or house with helium: everybody will asphyxiate.

Premise 4:
  • Following from Premise 1,2, and 3
    • Increases in the fungal load at the lowest (lens) level has only a small increase in the fungal load of the environment it is in - the camera bag in this case.
      • The possible magnitude of increase at that (lens) level is limited by resources:
        • A newly infected lens will follow boom and bust mechanics:
          • Fungus will expand as quickly as it can under the circumstances until available water is used up, at which point it will continue to grow, slowly, at a rate determined by the ingress of new water.
          • All stages are limited by respiratory gas availability.
          • The newly infected lens will exist in equilibrium with the camera bag:
            • Large changes to the fungal load of an individual lens will create a small change in the fungal load of the bag.
          • A small change in the fungal load of the bag can potentially have a large change on the fungal load of the lenses within it.
        • HOWEVER - the environment the bag is stored in, relative to bag itself has:
          • Massive volume
          • Massive resource availability
        • This results in a massive fungal load on the bag.
.

Conclusion:
  • Following from the above:
    • A massive fungal load on the bag from the environment will dwarf a fungal load on the bag from lenses within it.
      • Thus, the environment poses a considerably greater risk to the bag fungal load than the contents of the bag:
        • HOWEVER - if the environment is limited in fungal load or resources (exceptionally dry, for example), then the equilibrium shifts towards the lens-side of the equation.
          • Thus, we can conclude that the risk to lenses is greatest from the environment, but not zero from other lenses.
            • This is in line with your risk assessment:
              • Environment poses the greatest risk
              • Lenses increase the risk negligibly relative to the environment
                • Even a small increase in absolute risk over a long period of time still poses a threat.








So - the moral of this long and winding story is don't get your lenses moist in the first place - and if you do, you can prevent it spreading by limiting moisture in your bag.

---------- Post added 04-09-19 at 03:45 AM ----------

Sorry for the ramble... it was supposed to be a short reply! Dang my brain!

---------- Post added 04-09-19 at 03:46 AM ----------

Ps - that wasn't a rebuke btw! Merely an expansion and merging of our thoughts on the subject

04-09-2019, 07:27 AM   #17
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Oooh! The replacement lens just arrived....... aaand, the iris is skeewiff - it's egg-shaped.

Sure, I could get away with it, but I've instead decided to transplant the rear element from the bad-iris lens with the previously fungus lens - and now I finally have a good lens, and a spare to use in astrophotography.

Eesh!

What a palava.

My final goal is to give the previously fungally rear element group a dismantling and cleaning, which I might as well make a video of.

Side note - not really a problem in my case - but might any of you know the cause of/how to fix an aperture blade or two that doesn't seem to deploy correctly (resulting in an oval or in my case, egg shaped aperture)?
04-09-2019, 07:50 AM   #18
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QuoteOriginally posted by cprobertson1 Quote
but might any of you know the cause of/how to fix an aperture blade or two that doesn't seem to deploy correctly (resulting in an oval or in my case, egg shaped aperture)?
I would imagine someone has had the lens apart before, taken the aperture assembly apart and not re-assembled the blades correctly. if there is a bent blade that could be the cause for it to not close properly.

You know what the answer to your second part of the question is Take it apart, and re-assemble. It is a bit fiddly but not difficult.
04-10-2019, 12:08 AM   #19
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QuoteOriginally posted by pschlute Quote
I would imagine someone has had the lens apart before, taken the aperture assembly apart and not re-assembled the blades correctly. if there is a bent blade that could be the cause for it to not close properly.

You know what the answer to your second part of the question is Take it apart, and re-assemble. It is a bit fiddly but not difficult.
I do like fiddly things! I can't see any evidence of tampering on the outside of the lens - but that's not to say it's not there, merely that I can't see it :P

I'm not looking forward to having to delve that deeply into it again - the contacts on the mounting plate are free-spirited and never want to go back in their housings - but I'm pretty sure I need to remove that mounting plate to get the rear housing off to expose the traversing assembly with the iris on it.

In this case I can probably get away with leaving it - if it's going to be used as a star-tracking camera then it's not going to mater. My minolta lens (coincidentally, the lens that was originally going to share the same fate) has a squint aperture as well - I use it with a reverser as a macro lens - so it's never been a problem - but it might be hellfun to try to fix it.

That will definitely be a job for some other day though

04-19-2019, 03:53 PM   #20
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Just had an interesting addendum to the above lens repair/cleaning/surgery

I took it out today as a walkabout lens and discovered that the lens wouldn't focus more than maybe 10m away - turns out I had to do a little bit more surgery.

Didn't take too long to fix- just a matter of lifting off the rubber on the focus ring, revealing some black tape which I took off with a knife, allowing the entire front element assembly including the focus caddy to be lifted out - in my case it was just a matter of twisting the outer bezel (without taking it apart at all) and running a few tests outside to get the focus ring set correctly - and then I taped it back up with some mylar/kapton tape I cut to size.

For similar lenses (though to be fair, these are the only lenses in my collection that are adjusted in this way) the attached pic shows the (original) tape holding the bezel/caddy to the focus ring, and what I assume is a rule for calibration.
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