Oil-spaced Apochromats/ Objective Elements

I have been reading up on 5-6" refractors and some (like the TEC 140) have oil spaced objective lens elements. I beleive some of the older AP's might have it too. Question is what is the longevity of the oil? Most organic oils will eventually react (oxidize, turn yellow, change viscosity, cloud, leak). How risky is this for a high end refractor? Will wide temperature swings affect the stability of the film? I like the TEC a lot but I wonder about this oil thing.

Thank you in advance for your opinions.
Ivan

My understanding is that AP uses some pretty special oils that do not degrade, I imagine that TEC does as well. My suggestion would be to Email Yuri at Tec, he posts here, let him tell you...

jon

HI,

AP (until now), TEC and Zeiss use oil-spaced objective while TMB, TAK use air-spaced. Now, for TEC and probably others, that's not "oil" but a special two components mix sealed between lenses : neutral chemically and probably with silicone. It stays in by capillarity.

Please note "zero risk" does not exist. But risk with "oil" is not higher than risk with "air" : moisture between lenses (experimented with an old Perl scope), slight shift of a lens...

But risks with these well made scopes are very low. With my TEC140, I think the major risk is I fall with the scope in my hands...

Good luck,

Laurent