Re: Wider than normal lenses

[T3D Greg Erker <erker@xxxxxxxxxxxxxx>]

>angle lens I can get away with without imparting too
>much "squash"(?) (or is it streatch) into the image.

  Since John B isn't around I'll try to answer.

  You will get stretch when viewing with a longer
FL (than the taking lens).

>I will ONLY be viewing the images with a handheld
>viewer that has a 50mm F.L. lens.  I know the taking
>lens and viewing lenses SHOULD be the same and projection
>will do it's own thing with distortion, but in my
>restricted use, do you think a 28mm lens on a 35mm SLR
>(slide bar) camera would produce acceptable images.

  Your stretch will be 50/28 = 1.79 or 79%. For comparison
the Realist has 35 mm lenses and the Red Button viewer
has 44's which gives 26% stretch. This is noticable but
not objectionable to most people. The 79% stretch in
your situation will be quite noticable with familiar
objects but since no people are being photographed
you will probably be okay. (I haven't done this myself
so I'm guessing and repeating what others have said.)

>   I intend on determining the Basseline by the formula:

  I don't know about your formula, but you should get a
copy of John B's maofd spreadsheet. Using your 28 mm
lens and allowing 1.3 mm of on film deviation I got
the following results:

near=3 ft. far=12 ft. -> max baseline = 55.5 mm
near=3 ft. far=25 ft. -> max baseline = 47.4 mm

near=4 ft. far=12 ft. -> max baseline = 83.6 mm
near=4 ft. far=25 ft. -> max baseline = 66.5 mm

near=6 ft. far=12 ft. -> max baseline = 167.9 mm
near=6 ft. far=25 ft. -> max baseline = 110.7 mm

(The original spreadsheet has all units in metric.
I've modified my copy to allow near and far to be
entered in feet.)

  You don't have to use a baseline as big as the
above. It is just a maximum so that you don't exceed
the 1.3 mm on-film deviation.

  The stretch will enlarge thing in the depth dimention.
Using a baseline different than eyespacing will scale
everything in all three dimentions. So you may want
to use normal spacing and just ensure nothing is
too close (causing the on-film deviation to exceed
1.3 mm).

Hope this helps - Greg



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