Re: Optics question (not alt)

----- Original Message -----
From: <FDanB@aol.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Wednesday, March 09, 2005 3:58 PM
Subject: Optics question (not alt)

>
> Am I remembering something incorrectly or does image size
> on the
> film/chip plane change with aperture? I could swear it
> does but I don't
> know from where I pulled that info. Or, perhaps I'm just
> losing my mind.
>
> I'm helping a friend edit a chapter in his book and sure
> don't want to
> suggest something wacky.
>
> Thanks in advance for input.
>
> Dan
>
> www.danburkholder.com
>
> www.TinyTutorials.com
>
    I started out to reply to this earlier today and
completely drew a blank on a word I wanted. Its still gone
but I will try anyway.
    The size of the image does not vary with the stop.
However, some types of electronic imaging devices have each
sensor at the end of a small tube. These are sensitive to
the variation in angle of the light striking the tube. That
is, light which is not parallel does not get to the sensor.
Normally, the light leaving a lens is convergent. The angle
of convergence depends on the speed of the lens as well as
its distance from the focal plane. Lenses made for digital
cameras and similar devices are of a special type (the name
is the word that is escaping me). These are arranged in a
way that makes the light leaving the lens parallel, or
nearly so. This may be counter intuitive but it works. One
or the other of the pupils is extended in space. For the
digital camera it is the exit pupil, which is extended so
that it lies on the focal plane. For lenses used in countour
prjectors or for magnifying scales, it is projected onto the
suject plane. The advantage is that being slightly out of
focus does not change the size of the image. I am sure that
someone out there knows the name for this.
   The reason I have to go by memory is that I recently
boxed up much of my library so that repair work could be
done on the house and I haven't got the stuff out again.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com