RE: [OM] Long Focus vs. Mirror Lens

[Winsor Crosby]

>  > Cons are that it almost always has a fixed apeture
> >  (usually at f8 or so).
>  Why is this the case? I've only ever seen mirror lenses at f8, but what is
> it about the design that stops them putting aperture blades in there?
>
>  Also, how awkward _is_ this? f8's a reasonable aperture, I guess, but do
> you end up needing a lot of ND filters or something in practise?
>
>  (There's normally a few on e*ay for $130 or so; various brands, but they
> all look pretty much identical. I'm almost tempted, but the bokeh I've seen
> on mirror shots is so ghastly I'm afraid..)
>
>  -- dan
I think if you made one faster than f8 you would quickly lose its 
advantages.  It probably is not worth the cost to add an aperture to 
change it from f8 to f16 even if the secondary mirror does not make 
it  difficult.
--
Winsor Crosby
Long Beach, California

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