How to tell if lens has fungus or simply a lot of dust?

[hobbes187]

Hi all,

I was wondering how to tell the difference between fungus and dust particles? Cos after viewing some 2nd hand lens, when I look into the lens against a bright light with aperture wide open, I usually see specks and particles inside.

Problem is how to differentiate dust particles crowding together and fungus? Anyone has images of the 2?

 

[Rashkae]

Do a search here. This has come up many times. Or a google search for "lens fungus" will help you too.

 

[catchlights]

if you see things like spider web or tree roots, it is fungus

 

[hobbes187]

Hmmm... I see some dust has roots also if you turn the manual focus ring to focus on them... From far they look like a speck though...