[MF3D.FORUM:1483] Re: NSA MF slide show

["Bill Glickman" <bglick@xxxxxxxx>]

Tom

> If I have this correct now, you are telling me that the 50mm focal
> length you are referring to is for a lens or reflector used on the flash
> and not the lens used to produce the image for the film. Or are there
> two lenses of the same focal length, one for the flash and one for the
> film?

       With better electronic flashes, the flash has a fl setting on back
panel, most are automatic to enable them to work with zoom lenses...so on
35mm camera, you zoom to 60mm with the lens, the flash tracks it, and
adjusts its reflectors inside the flash to accomodate the field of view of
that fl lens.  This is why I mention the basic inverse laws get altered as
you are changing the light pattern for each fl.  This not true of a standard
buld bulb flash that fires the same regardless of the lens fl in use.

> This also does not change what I said about multiple flash lamps or
> multiple flashes of one lamp where the physical setup (camera and lamp
> locations) and optical setup (focal length, fStop, exposure time, flash
> duration) are unchanged. A subject which is twice as far away receives
> and backscatters one fourth as much light so four flashes will be
> required to make up for doubling the distance.

       Yes, I agreed with this, this assumes no changes to the flash in the
before and after example...but with electronic flashes there is a change,
hence my point....   These light beams can be so narrow that as I mentioned
before you can use a small flash, GN120 to shoot  a subject several hundred
feet away...  because the entire beam of light is focussed right at the
suject, with no wasted or scattered light on the way there, or at least
extremely minimized.

> It's party time now. No more Email for me until Sunday afternoon. Enjoy
> your evening.

Enjoy!

Bill G