At the risk of beating that dead ol' horse 8)
Oil spaced:
Two coated surfaces that can degrade or spot
No critical spacers
Less subject to mechanical shock
Modern "oils" are not oils and are extremely stable
Air spaced:
Six coated surfaces that can degrade or spot
Two critical spacing dimensions
Can be decentered/misaligned by mechanical shocks
Poor thermal stabilization in sizes above 20 cm
Air spaced offers the ultimate in correction (more degrees of freedom) if the designer is up to the task and the lens is executed to close tolerances. I decided on an oil-spaced lens because there is a quality source here in the USA, and the only available air-spaced apos in that size come from a factory in Russia, thousands of miles away.
Oil spaced:
Two coated surfaces that can degrade or spot
No critical spacers
Less subject to mechanical shock
Modern "oils" are not oils and are extremely stable
Air spaced:
Six coated surfaces that can degrade or spot
Two critical spacing dimensions
Can be decentered/misaligned by mechanical shocks
Poor thermal stabilization in sizes above 20 cm
Air spaced offers the ultimate in correction (more degrees of freedom) if the designer is up to the task and the lens is executed to close tolerances. I decided on an oil-spaced lens because there is a quality source here in the USA, and the only available air-spaced apos in that size come from a factory in Russia, thousands of miles away.
Jim McSheehy
