PanoTools:
Re: entrance pupil - nodal point
Rik Littlefield 2004-Nov-11 15:40:13
--- In #removed#, "David Sykes" <#removed#>
wrote:
>
> Rik Littlefield wrote:
>
> > The entrance and exit pupils are often defined as images of the
> > aperture as seen through the front and back lens elements. (This
> > definition fails, by the way, for telecentric lenses, whose
> entrance
> > pupil is effectively at minus infinity.)
>
> Not so !
> The definition is exactly right and it is why the magnification of
> the subject does not change even when out-of-focus (within small
> limits, but still far greater than conventional lenses).
>
> As Rik knows, I have a telecentric courtesy of Ebay.
> I have just looked into the front of it and can see (when wearing
my
> glasses for distant vision) the entrance pupil at infinity.
>
> Not sure if it is plus or minus infinity though :-)
David is quite correct. I don't actually have one of the beasts, and
my imagination failed me.
--Rik
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