From: ohk@nta.no (Ole-Hjalmar Kristensen TF.DT/DELAB)
Subject: Re: Binoculars for Hunting: Leupold, Nikon, etc???
Organization: Norwegian Telecom Research

In article <3a7hsq$m9q@whitbeck.ncl.ac.uk>, "J. Spencer" <J.M.Spencer@ncl.ac.uk> writes:
|> johno@vcd.hp.com (John Ongtooguk) writes:
|>
|> #J. Spencer (J.M.Spencer@ncl.ac.uk) wrote:
|>
|> #: ObUsefulTip: for a given quality of lens, roof prism binoculars let
|> #: more light reach the eye than do porro prism binoculars. (Roof prism
|> #: binos have straight bodies, proor prism glasses have the 'dog leg' in
|> #: them.)
|>
|> #  Actually it's the other way around; the best roof prism glasses
|> #  can equal good porro prism models, but given equal quality the
|> #  porro prism models will have better transmission.
|>
|> That's the opposite of what Zeiss and Optolyth say in their brochures.

Zeiss said otherwise about 10 years ago. So did Leitz. I remember the marketing
hype about  "thanks to new and advanced coatings our roof prism models now
equal the quality of our porro prism models".


|> #  As I recall
|> #  the roof prism models have an extra reflection in the light
|> #  path,
|>
|> I don't have the diagrams to hand - and ASCII wouldn't cut it anyway -
|> but the porro prism design is inferior to the roof prism design because
|> the position of the prisms makes the light "go round more corners". The
|> roof prism prisms (is that too many prisms? :) sit "back-to-back. The
|> porro prism design forces the light to "dog leg".

Doesn't matter much. What matters is the number of reflections and the surface
coatings of the optical elements.


|> A layman can draw his own conclusions from the prices of equivalent
|> devices: roof prism are always more expensive. Why might that be:
|> because they are inferior or because they are superior?
|>
|> --Jonathan


Because you have to do more work and use better coatings to get comparable
quality. Also, because binoculars with roof prisms are less bulky, and more
attractive to the customer.

Ole-Hj. Kristensen