Re: Why no other "Petzval" apos?

From: Bill McHale (wmchal1_at_umbc.edu)
Date: 11/30/04 

Date: 30 Nov 2004 12:56:24 -0800

RichA <none@none.com> wrote in message news:<ln7nq0p6aa363ajn3986oo3toj77nlrr8u@4ax.com>...
> TeleVue has more or less been the only ones
> using this for apos, with the other makers
> doing only full size lenses and no sub-diameter
> lenses. I think the only competition with the
> kind of speed the TeleVue has is from Pentax.
> Other than that, Tak has the FSQ and Vixen has
> some scopes that are similar. But no one else
> has come out with a long focal length primary,
> sub-diameter corrector "secondary" lensed apo.
> It seems like it might be more economical than
> a full aperture triplet but I guess it depends
> on the glass, mechanics as well.
> -Rich

Well Tak FSQ and Vixen DED scopes are both pretty fast. And mind you
Tele Vue only uses the Petzval designs for the 101 and the 127; the
rest of their scopes (AFAIK) use doublet designs.

My guess is that the design is in fact not cheaper than most triplet
designs out there if for no other reason than the fact that you now
have 8 optical surfaces to figure instead of 6. Further two of the
optical elements are rather deep in the tube that will add additional
challenges to mounting and aligning the lenses. 

--
Bill

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