Don,
At 3:22 AM +0000 10/11/03, olympus-digest wrote:
>Date: Fri, 10 Oct 2003 14:45:28 -0700 (PDT)
>From: Donald Shedrick <shedridc@xxxxxxxxx>
>Subject: Re: [OM] E-1 lenses resolution vs. conventional lenses - fact or hype?
>
>I am not sure about the argument about the angle of incidence of
>light onto the CCD surface. As I understand it, with an OM lens on
>an E-1, only the central portion of the lens would be used due to the
>CCD's size and the angle of incidence would be more perpendicular
>than it is when the lens is used for film in an OM camera.
While it's true that when one uses a 35mm lens on a 4/3 CCD camera, only a part
of the original 35mm image frame is used, but it doesn't matter. Unless the
lens is telecentric in the image space (between lens and CCD), to a first order
angle of arrival of light depends only on the focal length and the dimensions
of the imager's sensitive surface. To a second order, the range of angles of
arrival depend on the location and size of the back lens (closest to film or
CCD) with respect to the sensitive area of the CCD or film.
The bounding case is to draw a cross-section of the lens and imager, with the
cross-section cut on a diagonal of the sensitive surface (image frame), so we
can see right out to the corners of the frame. The cross-section plane must
include the optical axis of the lens. Draw two lines, from the extremes of the
back lens to one of the frame corners. At what angle do those lines intersect
the image plane at one of the corners? The larger of the angles will tell how
much light loss to expect from the restricted acceptance angle of the CCD.
(The full computation will be more complex than this, because one also suffers
cos^4 loss and internal lens vingetting and so on. But it all adds up.)
Anyway, the longer the focal length of the lens, the less the problem.
Joe Gwinn
>- --- Joe Gwinn <joegwinn@xxxxxxxxxxx> wrote:
> > At 3:20 AM +0000 10/10/03, olympus-digest wrote:
> > >Date: Thu, 9 Oct 2003 18:19:49 -1000
> > >From: "Danrich" <danrich@xxxxxxxxxxxxx>
> > >Subject: Re: [OM] E-1 lenses resolution vs. conventional lenses -
> > fact or hype?
> >
> > It's a tradeoff. What those manufacturers meant was that they
> > produced the best resolution (for the price). Far better lenses
> > are possible, but not at a price (or weight) suited to photography.
> >
>[snip]
> >
> > What is different is that the KAF-5101CE CCD has a microlens on
> > each pixel, limiting the allowed angle of incidence of light onto
> > the CCD surface to something like +/- 5 or 10 degrees from
> > perpendicular. How wide an angular range is acceptable depends on
> > how much light falloff in the corners is acceptable. Anyway, film
> > has essentially no angle restriction, so lenses with short focal
> > lengths can be a problem with such CCDs, in that the corners may be
> > darker than with film, and Olympus may not wish to attempt to
> > explain the reason the the mass market.
> >
[snip]
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