james_f64

james_f64

Lives in United States San Diego, CA, United States
Joined on Jun 5, 2008

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james_f64: Even today Petzval-like designs are used in some of the most highly corrected and expensive telescope objectives that you can buy. I'm talking about diffraction-limited, wide-field telescopes that can cost anywhere from $4,000 to $8,000, like the 4" and 5" aperture telescopes from Tele Vue (U.S.) and Takahashi (Japan).

I'd suspect that a properly designed Petzval of modest aperture using low dispersion glass could perform quite well even by today's standards if used under a restricted set of conditions. At its limit, however, it will likely be larger and heavier than your typical modern telephoto design.

Actually, the Petzval telescopes are designed for flat-field astrophotography (that's their sole purpose for being). Also, since they are designed to be astrographs they can cover fairly large fields even without correctors. At least up to APS size (on the Tele Vue) and even wider on the Takahashi, they don't need correctors. The Tele Vue has a corrector for full-frame 35mm or larger and both accept reducers that increase their photographic speed by about one f-stop (but the latter aren't used as a "field corrector," they are instead focal reducers).

Here is a review that compared a Tele Vue Nagler-Petzval against a Canon 600mm/4.0L IS:

http://www.samirkharusi.net/televue_canon.html

This was a full-frame 35mm comparison and the Tele Vue did NOT use its available large frame corrector. The reviewer said that while the Canon lens was superior at the edges of the frame the Tele Vue delivered a better image in the center and was likely to be fully satisfactory over an APS sized field.

Direct link | Posted on Jul 26, 2013 at 11:35 UTC

Even today Petzval-like designs are used in some of the most highly corrected and expensive telescope objectives that you can buy. I'm talking about diffraction-limited, wide-field telescopes that can cost anywhere from $4,000 to $8,000, like the 4" and 5" aperture telescopes from Tele Vue (U.S.) and Takahashi (Japan).

I'd suspect that a properly designed Petzval of modest aperture using low dispersion glass could perform quite well even by today's standards if used under a restricted set of conditions. At its limit, however, it will likely be larger and heavier than your typical modern telephoto design.

Direct link | Posted on Jul 26, 2013 at 08:15 UTC as 34th comment | 2 replies
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