Re: Please explain this weirdness


"dave fenner" <dffenner@xxxxxxxxxxxxxx> wrote

I am retired cinema projection engineer. Years ago carbon arcs were
ubiquitous, 12" or bigger mirror with central hole for -ive [???] carbon,
arc gap about 3/8", positive carbon co-axial,. hotspot facing facing
mirror about 3-4" away, 2nd focus at the aperture about 32" forward.

When viewed from the side, when smoke present the cone shaped beam
mirror to aperture appears to have curved sides! The beam appears
shaped like an exponential horn, a trumpet.

I have heard but cannot remember a word to describe this. Now I talk
to a current day cinema engineer who knows only xenon lamps (no smoke)
and he wont believe me about this, and of course I do understand why.

Someone please tell me the name of this effect, where I may find
illustration or explanation. TIA.

Spherical aberration should explain at least part of what you are observing.




.

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