Re: matching camera lenses

[P3D Sam Smith <3dhacker@xxxxxxxxxxxxx>]

At 09:37 PM 13/3/97 -0600, you wrote:
>I've been wondering. On the one hand I see Sam's 3D Hacker web page, 
>where I get the impression that as soon as he finds two cameras of 
>the same kind, he joins them and creates yet another wonderful 3D 
>camera. 
>
>On the other hand, there are the discussions here that lead me to 
>believe that the lenses must match exactly, or 3D isn't possible. 
>

Sometimes people get the impression that I take any two cameras at random
and make a stereo camera out of them. There are a few times I'll chance an
imperfect match, but most of the time I'm VERY PICKY as to which lenses I'll
use. Bodies are no big deal, as any two of the same model will do. I've had
to buy 5 cameras for a particular MF Stereo project in order to get two
lenses I was happy with. Keep in mind you can always build the body first,
then switch lenses later.

3D IS possible with almost ANY two lenses, as long as the two images were
taken from the same vantage point. When it gets to the viewing stage though,
things can get a little complicated. If you're making prints, you simply
enlarge both images so they're again compatible, which may mean enlarging
one slightly more than the other. It's slide users that will run into the
most problems. Perhaps if you only used the one camera and only one viewer,
you could vary the focal length of each viewing lens to compensate. But this
will mean each pair would have to have one image closer to the lens than the
other.

The other option on unmatched lenses is to have two different planes of
focus. The Stereo Graphic operates on this principal. You set one lens, the
one with the longer focal length, to  the farther distance, say 20'. The
shorter lens would be focused on a nearer plane, say 10'. Having a depth of
field of say f16 will eliminate any DOF problems, and the lenses should
produce images of equal proportions.


>I'm wondering which impression is the most accurate, at least in 
>practical terms. I've got two Pentax KXs that I'd like to use for 3D, 
>but I doubt if I can find a merchant that will let me "try 
>out" half a dozen lenses until I can find two that match perfectly. 
>If, by the luck of the draw, I get two lenses that are _not_ matched, 
>will I be able to use them?

Find someone else who is interested in the same project! Wide angle lenses
are the worst to match for me, but standard lenses aren't too extreme.
Fortunately standard lenses are usually the cheapest anyway, so even if you
had to buy another, it would still make the project worthwhile. And if it
turns out REALLY good, everybody will want one anyway!!!!


Sam


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