Re: Poll on *Really* Wide Angle Lenses


Nostrobino wrote:
- Lots of stuff snipped -
>
> Well, he's saying that light falloff at the edges can be not only reduced
> and eliminated but even *reversed*, the edges becoming brighter than the
> center, by some means of lens design. I just don't see how that's possible
> unless, as I mentioned, the aperture can be made effectively larger (and in
> the case of extreme wide angle lenses, *much* larger) progressively as the
> off-axis angle is increased. I have no idea whether that's possible or not.
> But he's a lens designer and I'm not, so I'm sure he knows a lot that I
> don't know about this subject. On the other hand, if I understand him
> correctly, the lenses he says he's designed that do this have never actually
> been produced.
>
>

Actually, I'm not just *saying* that illumination falloff can be
eliminated in rectilinear lenses, I know that it is incontestable fact.
A fair number of my design projects have dealt with DMD and LCD
projection lenses. These lenses are characterized by having extremely
low distortion and *very* uniform illumination. Performance in these
two areas is drastically better than any photographic lens on the
market. A key reason why is that projectors are often used in video
wall applications (tiled rear-projection screens), where even a tiny
amount of distortion or falloff would be noticeable. I've not only
designed wide-angle projection lenses, but have also actually measured
the falloff characteristics of the manufactured article.

Its true that most of these projection lenses have a "field" angle less
than 90 degrees. Its also true that the special ultrawide rectilinear
lenses I brought up in this thread have not yet been built. However,
lens design software is exceedingly accurate in predicting many aspects
of lens performance, including relative illumination. Questioning the
validity of the calculations really doesn't make much sense here.

On the other hand, I can certainly sympathize with curiosity and a
desire to understand new things. No one seems to have paid any
attention to the two explanations I've already provided - one based on
the cos^4(theta) rule, and the other based on the fact that the
diameter of the off-axis ray bundles entering the lens can be larger
than the on-axis bundles. The physical aperture stop itself is
obviously identical for all obliquities so long as vignetting is zero.
And in a lens with uniform illumination the off-axis f/#'s, best
defined as the sine of the extreme ray angles with respect to the chief
ray, must be virtually identical to the on-axis f/#. I simply cannot
explain this subject any further without resorting to making drawings,
which isn't practical for me at the moment. If you really want to
understand the subject then you should ask specific questions based on
my explanations.

I'm not making this stuff up. The designs I have absolutely will
behave as predicted. Care to donate about $30K to help me build some
prototypes?

Brian

.

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