Fungus spores are everywhere, but they only germinate in humidity and they thrive on dust.
A lens that has a dose of fungus has it because it has dust inside (and all lenses have some specs of dust even if they’re hard to see), and it’s been kept in a humid/warm environment. Fungus likes dark, damp places with warmth. Fungus generates spores which look to feed on dust, but the amount of dust in most lenses isnt enough for the fungus to spread.
When you clean a lens you move the dust around and push it into the edges. If the lens is then stored in a humid environment it’s more likely to encourage fungus growth. The fungus wont spread from lens to lens but it may appear in other lenses if the conditions are right for it.
So it’s best to store your lenses in a dry place in good light with minimal humidity. Also use them – the UV in sunlight kills fungus.
The above photo shows one patch of familiar fungal veins. This is on a rear element and is hard to spot without scrutiny.
The best way to check for fungus is to shine a bright light in through the front or rear. A mini torch such as a Maglight is ideal.
Can fungus spread from camera lens to lens?
Does lens fungus spread from one lens to another? It’s a common question. Much is written about the subject on the internet…and views are mixed – some saying yes it does spread so you should isolate the infected lens and some say no, don’t worry about it.
Using infected lenses
You can often clean fungus off the lens elements providing it’s not etched into the coating. If it’s on the inner elements you’ll need to strip the lens down but only attempt that if you’re competent with mechanical items as they’re not always as simple to take apart as they look.
If the lens is stored well once fungus is found it’s unlikely to spread.
Lenses can be used and results will vary depending on the level of contamination. A small colony here or there is hardly likely to affect anything while a more severe case will cases a dramatic reduction in contrast and sharpness, especially when shooting into the sun.
This lens is badly affected and will result in lower contrast photos that lack sharpness and have a diffused look.
For those who want more info check out this informative web page: All about lens fungus