Re: [photo-3d] To Zoom or not to Zoom?

["Dr. George A. Themelis" <drt-3d@xxxxxxx>]

Hi Jay,

>Up until now I've been using a pair of 50mm lenses with my twin Canon
>set-up...but I've been wondering whether I could use zoom lenses or not. I'm
>assuming it would be fairly easy to use the extremes...28mm and 90mm, for
>example, with a 28mm-90mm zoom...but how does one make sure both lenses are
>the same for all other lengths? Is it enough to rely on the printing on the
>lens barrel? I don't see how I could ever be sure that both lenses were set
>exactly the same. How much does it matter?

If you had asked me a few years ago I would have said
to skip the zooms.  Even at the extremes you do not
know if the focal lengths are matched.  Since then, I
had an RBT camera with zoom lenses which have the
focal length adjustments linked and I was very happy
with the results.

How much does it matter?  This is up to you and your
application to determine.  This question in the form
"how much mismatch can be tolerated?" has been asked
before, without any definite answer (other than the
obvious "zero").

Here is what you can do:  Put the cameras side-by-side
on a tripod and check different zoom settings by 
observing (very carefully) the scene while looking
through the viewfinders.  Find settings (the marked
FLs is a good start) that show the same exactly scene 
(concentrate at tops and bottoms of the viewfinder).  
Mark these settings.  Then use film (negative film 
and prints will be fine - even better) to take 
pictures at these settings. Make adjustments as needed.  
At the end of this process you should have a few pairs 
of acceptable to excellent matching.

Good luck!

George Themelis