[MF3D.FORUM:1265] Re: MF3D Projection

[Tom Hubin <thubin@xxxxxxxxx>]

Hello Sam,
 
> My concerns about MF3D projection are a little different. I would expect
> the amount of light for projection would be reasonably intense, even though
> the magnification would not be as great as in 35mm. 

Assuming the same technology for optics and lamp, the filament area, the
electrical power to the lamp, the optical power to the slide, and the
area of the slide would all scale equally. So the light per square mm of
slide would not be different even though the total light through the
larger slide is greater.

Since the image on the screen is about the same size for 35mm or MF, the
MF image must be brighter because the total slide had more light.

> Mounts unsupported with
> glass would have very little support at all, so when the slide heats up the
> film would in turn start bowing out from the center and render part of the
> image out of focus. 

Heat is mostly caused by IR, not by white light. A tungsten or halogen
source produces about 90% IR and 10% visible light. IR is usually
filtered out as much as practical with IR absorbing glass or hot mirrors
or cold mirrors. But the more IR you try to eliminate, the more visble
light you loose because the filters are not perfect. But todays filters
are much better than the 1950's filters.

Block the light coming out of a 1950's vintage TDC116 or TDC716 with
your hand. Feel the heat. That is mostly IR due to poor IR absorbing
glass. Do the same for a modern Brackett Disolver or a Kodak Carosel.
Very little heat felt. Good Schott KG1 glass used for IR absorption.

Some heat on the slide is due to lots of visble light absorbed by dark
scenes. But most of the problem is IR. Eliminate the IR and forced air
cool the slide, if necessary, and hot film should not be a problem.

The slides are larger and may buckle more anyway. But the focal length
of the projection lens is also longer and so is the depth of field. So
it may not matter if the warping of the slide is a scaled version of
35mm warping.     

Tom Hubin
thubin@xxxxxxxxx