[opendtv] Re: Red camera lenses
- From: dan.grimes@xxxxxxxx
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 13 Jun 2007 13:08:50 -0700
Though your question might be rhetorical, there are lenses that do not have
focal points.
If you are talking about a "lens" as a single element, there are lenses
that do not have a focal point where the light diverges but rather
converges. But the divergent lens would have a negative "focal point" even
thought the light never converges. An example would be a biconcave lens.
So one might argue that this still has a focal point. Ultimately, if the
positive or negative focal point is infinite, then you would have a
"filter" and might not define it as a lens.
As far as a system lens, a lens made up of many elements, there aren't too
many lenses that produce an image that do not have a focal point. There
are conversion optics that do not have a focal point, but they do not make
an image by themselves. There are some rare designs that do in fact
"image" without a system focal point, but I don't think there are any in
the broadcast industry.
Dan
From: "johnwillkie" <johnwillkie@xxxxxxxxxxxxx>
Subject: [opendtv] Re: Red camera lenses
Date: Tue, 12 Jun 2007 11:27:48 -0700
"In some lenses, light may radiate from a central point within the lens
and travel in non-parallel lines to the sensor."
Seems to me that glass without this characteristic cannot be called a lens.
Is there a lens without a focal point?
John Willkie
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