PanoTools:
Re: entrance pupil - nodal point
Rik Littlefield 2004-Nov-11 16:30:18
--- In #removed#, "David Sykes" <#removed#>
wrote:
>
> First of all, the entrance pupil is the image of the LIMITING
> aperture as formed by the lenses in front of it, if any.
> Just what constitutes limiting aperture can change with subject
> distance and angle, it does not have to be the iris diaphragm.
>
> Anyway, why don't we just measure it ?
> So, I have.
>
> I illuminated Sigma 8mm fisheye from rear via translucent film and
> red filter.
> Using a simple achromat, I projected an image of the entrance-pupil
> onto a screen.
> The rear surface of the projection lens was 42mm from the sigma
front
> element.
> I replaced the Sigma with a needle and adjusted it's position so
that
> it was in-focus.
> The needle was 61mm from projection lens.
> So, when perpendicular to the Sigma, the entrance pupil is 19mm
into
> the lens.
> That is about 0.5mm on the camera side from the gold band.
>
> I will try this more accurately and at various angles.
An alternate approach using a laser pointer is illustrated at
http://michel.thoby.free.fr/Liste-experiments1.html . Presumably the
two methods would yield the same result, but it would be nice to
confirm that, and also to know the relative errors of the two
approaches.
--Rik
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