Hey Dave,
This is a good question. I can't definitely tell, but it seems like they are on the outer side. The lens is Contax Zeiss Makro-Planar 100mm f2.8 to be exact. The lens is multicoated. I'll try taking some picture later today, but it will be really hard.
Cheers,
Zang
Zang,
If your lens were a Nikkor F-bayonet, EL-Nikkor enlarging lens or Nikkor-W, SW or M view camera lens from the 70's and later and probably most and maybe all from the mid 60's I would recommend using Regent Grade Anhydrous Methyl Alcohol as a lens cleaner. Please verify this as I'm not at home to check but I recall this form of alcohol was recommended in a Nikkor-W Instruction Manual that came with my Nikkor-W 210mm f/5.6 and other Nikon view camera lenses. Methyl alcohol should NOT be applied to any painted surfaces as it is or was the primary ingredient in Lacquer Thinner. I am not sure about plastics used in modern AF Nikkor lenses.
A counter indication: I used anhydrous methyl alcohol on a Schneider 135mm f/5.6 Componon-S enlarging lens with a vintage of 1973-74 and the methyl alcohol stripped the flat black paint between the filter threads and the glass surface. I smeared the black paint on the surface of the glass. It was easily cleaned off the glass and I re-blacked the area the paint came from. This is why I asked about the maker and age of the lens.
Multi-Coated lenses reflect less light from their surface compared to single coated lenses so minor impurities, smudges and swirls on the surface are more easily seen as these frequently reflect more light than the lens surface. A careful inspection of single-coated lenses can reveal that smudges and swirls are present.
When multi-coated lenses first came on the market people used soap based lens cleaners like Kodak Lens Cleaner and complained that multi-coated lenses were difficult to clean. In my experience they are not more difficult to clean when the correct lens cleaner is used. Distilled water was frequently recommended as a cleaner but distilled water is not a solvent of grease and oil so its effectiveness is limited.
Methyl alcohol is an aggressive solvent of grease and oil and regent grade methyl alcohol is 99% + pure and free of particles down to a few microns. It is expensive at around $30.00/500mm (USD). Methyl alcohol is an effective lens cleaner for lenses on which it is safe to use. I'm quite sure I've used methyl alcohol on a 1969 vintage 50mm f/1.4 Nikkor-S and other Nikkor lenses of that era with no problems.
Dave
Away from home, I've been using 91% isopropyl alcohol as a lens cleaner. Any comments?