RB67 140mm Macro Lens: Severe Fungus on Most Elements
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This is a post about lens fungus. I am servicing a Mamiya 140mm Macro lens that has a very bad case of fungus on almost every lens element. Photo two is looking at the lens from the rear. Photo three shows a close up of fungus on the floating doublet and you can also see lots of fungus debris on the side of the lens. This organism has been having a good time deep inside of this lens. Fortunately, most of the fungus cleaned off with lens cleaner as seen in photo four.
Since I like to look the enemy in the eye, photos five and six show what they look like at 150X.
Photo seven shows the lens in a dead air cabinet (this cabinet is also handy for assembling lens elements as it is dust free) along with a Mamiya Universal body. Both of these are being exposed to a UVC germicidal lamp to kill any organisms on the surface. The Mamiya Universal has a semi silvered mirror that can be easily damaged if physically cleaned and this one has fungus on it. If you are interested in technical info on the setup: CBS Scientific PCR workstation, P-0303-202, (2) 15 watt 254nm wavelength bulbs, power of app. 425 µw/cm2 at 12 inch distance, dosage of thirty minutes.
I generally don’t take in a lens just for fungus removal since many times the elements are damaged and can not be restored to perfect condition. Sometimes not even close to perfect.And you can’t tell until the lens has been disassembled. When a lens is being serviced I will make every attempt to clean all surfaces of contaminants.
There is no shortage of videos on the internet showing UVC light used to kill fungus in lenses by shining the light into the lens. This will not work because UVC light will certainly kill living organisms on a surface (with correct power and dosage) but is blocked by the glass in a lens. Photo eight shows a UVC meter on the left with the UVC bulbs turned on and on the right (showing zero power) with a thin 0.025” Kodak Slide Cover Glass over the meter sensor.
