P3D Re: Hummingbirds

[Tom Hubin <thubin@xxxxxxxxx>]

Dave Williams wrote:
> 
> Dr. George A. Themelis wrote:
> 
> > I'll tell you how the experts do it... They use twin SLRs with
> > longer lenses (say 135 or 200 mm lenses).
> 
>         I didn't think of that.  I guess my thinking was locked into the need
> for a smaller stereo base for closeup work.  Is it that the longer the
> focal length, the wider the stereo base needs to be for "normal"?  How
> would I calculate the base for something like this?  Or would twin SLRs
> next to each other with 200 mm lenses be close enough for  closeup work?
> 
> Dave

If you want the same size image and stereo perspective then the object
distance and stereo base are proportionate to the lens focal length.

One small difference in the results. If you are close to your subject
then the wing that is close to the camera will be imaged larger than the
wing that is far from the camera. If you are far from your subject then
both wings will image about the same size. I'm not saying one is better
than the other. Just letting you know that the results are not
identical.

Close also does not work well for a large aperture because small depth
of field will make it difficult to keep the bird in focus. A small
aperture makes focus easier but now you need a lot of light. This could
annoy the little guy.

If you use a long focal length lens and back away from your subject then
you can use a large aperture, get long depth of field and easy focus,
collect lots more natural light.

Seems like the long lens is simpler.

Tom Hubin
thubin@xxxxxxxxx


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