Bill is correct. Image magnfication with the same focal length lens
will be the same as long as:
a) the distance from film plane to lens or
b) the distance from lens to viewing screen is the same
These two things are simply differnt aspects of the same bit of lens
math. With a fixed focal length lens as soon as one is set the other is
determined as well.
To change the magnification without changing the projector lens to
screen distance would require a shorter lens for greater magnification
or a longer lens for lesser magnification. In other words, a zoom lens
to change the magnification while you and the projectior sit in the same
spot.
Aperture controls only the brightness except that it may also have an
effect on image quality just as it does with your taking lenses. A lens
with larger aperture needs to be better designed and built to have equal
image quality to a slower lens.
Other things that control brighness are the strength of the projection
bulb, the efficiency of the condenser system and the magnfication. If
you make the image larger you spread the total available light over a
larger area and make it dimmer.
Chuck Norcutt
NSURIT@xxxxxxx wrote:
>
> In a message dated 10/16/2005 10:11:45 A.M. Central Daylight Time,
> simon@xxxxxxxxxxxx writes:
>
> Could someone please confirm that if 90mm lens on current projector
> gives me the correct projected image size, then 90mm lens on another
> projector will give the same projected image size, even though aperture
> is different?
>
>
>
>
> Simon, the aperture should have no affect on the image size. Assuming the
> distance from the projector to the screen or surface project on is the same,
> the image size should be the same. That is all accurate unless I've lost my
> mind and there are those who might say that is the case. Bill Barber
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