At 03:57 PM 24/10/01 -0400, you wrote:
>I'm looking at projecting an image of the skyline across the distance of
>3 to 6 feet within a tube (oversized camera lens) I would like to keep
>this focal length small to keep the housing small but would also like
>an image of about 12 to 18 inches in diameter. Ideally, this lens
>configuration would allow a depth of field to accommodate focus on
>the skyline and on people in front of the 'camera'.

Kent,

You're setting yourself quite a problem here, as you are combining opposites:
a longer focal length (usually in mm or inches, but yours is in feet)
essentially means more magnification and less (much less) depth of field
you'll need a very large lens to make the image bright enough. Again you
will have problems with depth of field (very large diameter to focal length
= wide "f stop" = minimum depth of field)

You might consider something done with one or more mirrors. This would
allow you to reverse the image, and also to set the lens above people
height. Everything would be distant, so no depth of field worries. The
magic of a real image projected on a ground glass (get a good one) will
compensate for many other sins. Beside's a large lens at ground level would
be putting a substantial investment in harms way. The mirrors would
elongate the path for a telephoto effect without taking up valuable floor
space. The ground glass screen could be positioned and angled for maximum
visibility and in the darkest possible area (very important), and again,
out of harm's way.

a full scale mock up means a proper lens. Why not make a working smaller
scale mock up? The effect on the viewer will be the same.

You might find an amateur telescope maker to grind a lens for you. You
don't need a camera's or good telescope's compound lens system for
chromatic correction, just a simple single convex lens would do. Please let
me know (off line) what you decide to do, and contact me off line if I can
be of any help dreaming this.

js
[log in to unmask]

Jerry Shiner
Keepsafe Systems
Microclimate and Oxygen-free storage supplies and solutions
www.keepsafe.ca
toll-free 800 683-4696  fax: (416) 703-5991

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