At 05:36 AM 4/11/2005, Andrew Fildes wrote:
>Even better if that's possible - the air spaces involved are far
>shorter and lower in volume so less atmospheric haze and fewer aerosol
>pollutants are involved.
>AndrewF
I'm certain that the shorter the tube, the better the optics.
To take this down the slippery slope . . .
If an extension tube were cavernous enough, it would have its own internal
weather system, including fog and precipitation. Blimp hangars create
their own internal weather.
More seriously . . . the optical qualities of an extension tube are:
(a) Maintaining front and rear flange parallelism (when in use)
(b) Maintaining axis of lens to center of film gate (not quite as
important as [a])
(c) Having sufficient internal diameter to not impinge on the light cone
(d) Having extremely low internal reflectivity
-- John
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