Nikon Df with Ai Zoom Nikkor 25-50mm f/4 lens.
I love these old Nikkor Non-Ai & Ai lenses: unfortunately since the advent of mirrorless cameras, the price has gone up a lot. There are some bargains, but careful consideration of the condition & most importantly! lack of lens fungus needs to be taken into account. Even a small amount untreated, will migrate to any other lenses/camera you have in your bag. If your storage conditions are not good, high humidity & darkness will promote growth.
David A Lockwood 
What an amazing tree. On the subject matter how do you know you lens fungus? Is it visible on the camera and what damage can it do?
Hi, only got my phone at the moment, will give you info in a couple of days. It involves using a bright light with fully open aperture.
See my answer below for damage, from Nikon & Zeiss.
Thank you.
Done 🙂 and look at the K.R link – yes I know some think he is over the top sometimes but in this case he has a very good post.
Oh? What is this lens fungus you speak of?
The easy way to explain is from:
Nikon & Zeiss service info:
Fungus means an Infestation of optical instruments with fungus spores which germinate and produce more spores. Lens surfaces are irreparably damaged by metabolic products of the fungus (e.g. acids). Its damage ranges from cloudiness to opacity caused by the film. The coating has no significant influence on fungus growth or generation of spores.
Where does fungus come from?
• Fungus spores are everywhere and germinate under suitable environmental conditions:
• Growing conditions
• Relative humidity of at least 70% (more than 3 days)
• No or little airflow
• Darkness
• Nutrients (textile lint, traces of grease, varnish, dust and dirt)
Coming from Oman, it was something I took particular care about, high humidity & temperatures. Although using or exposing the lenses to sunlight was a recommended prevention (info from Nikon service agent there)
In general terms, most people will never see it and unless storage conditions are bad, cross-contamination is minimal.
P.s I added a bit to the image comment, so thanks for the question.
Oh wow, thanks for your detailed response. Since I tend to spend lots of time in humid climates, the information you posted about lens fungus might really come in handy.