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Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 07:31 pm: | 
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On certain of the New FD lenses that contain large diameter elements, Canon 'glue' the glass in place before locating the screw/spring ring. Examples of lenses so treated are 500mm/f8 Reflex and 200mm/f2.8 internal focus. The retaining compound is described in the official English manuals as 'Water Soluble Bond', however I have had a Japanese manual translated and the description becomes 'Water Based Bond'.
As I have always found that ethyl alcohol dissolves the bond, I have assumed that the bonding agent is PVA or some longer chain polyvinyl. I recently acquired an unused, in original packing 500mm/f8, which unfortunately has been stored in the leather case for 20 odd years and thus has a few spots of fungus on the front element.
The bond seems to run around the complete circumference, instead of just three small areas and does not/seems not to dissolve in alcohol.
Before I try the water route, does anybody know the actual chemistry of the bond or if water will dissolve said bonding agent? |
Reiner
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 25, 2006 - 11:53 pm: |
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I do not know the chemistry Canon used for their FD lenses but I might give some cents of my experience with paints. The difference between "Water Based" and "Water Soluble" is perhaps the key of this problems. From time to time I used water based paints. They are mostly based on polyacrylics or on polyurethane. These paints are water dilutable when still wet. When they are dry it is next to impossible to resolve them again. At least I have never succeeded to clean residues on a brush. I tried alkohol, lighter fluid and brush cleaner. I have not tried acetone but I would hesitate to use it in a lens. Sorry that i can not give you an answer more helpful. |
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