[photo-3d] Re: Camera separation in stereo photography (Stereo Bight)

["Ray Moxom" <raymoxom@xxxxxxxxxx>]

George Themelis wrote:
> I remember this topic coming up in the 3D Window, the
> excellent newsletter of the Sydney Stereo Camera Club.
> Unfortunately, I cannot find the specific copy right
> now (Ray Moxom, the Editor, can correct me if I am wrong)
> but I seem to remember that someone concluded that
> there is no such thing as "optimum separation", a
> theory to which I always subscribed.  In the following
> issue, a letter by Steve Spicer (of the famous "Spicer
> Mounts", carried by RMM) replied by saying that there
> is such an optimum separation and this is the spacing
> of the eyes. (I might be oversimplifying here, so Ray
> please correct me).

How could I resist replying to this one. The topic of lens separation and
'Stereo Bight' will always be contentious - even among friends.

My brief comments are below. The articles that George refers to have been
added to this list's web site at: http://www.egroups.com/files/photo-3d/ as
a 'pdf' file under the title of 'Stereo Bight'.

My opinion is that there is no such thing as a correct lens separation for
stereo photography.

Most stereo shots seem to work anyway. However, some have distortion because
the subject was too close for the separation and some are relatively flat
(ie they lack "stereo bite") because the nearest element in the picture was
too far away for the lens separation. The acceptable range of lens
separations is quiet large.

If the lens separation is 63mm (eg Verascope F40, RBT XnA and other European
format cameras) then there is a little less distortion in close subjects,
particularly of people, and less "stereo bite" (ie stereo effect) if the
nearest element in the picture is further away.

If the lens separation is 70mm (eg Realist format cameras) then the close up
distortion is a bit greater and there is a bit more "stereo bite".

However, an RBT XnB camera with 76mm separation can also be used to take low
distortion people shots - just move back and zoom in to 70mm focal length.
It all goes back to the closest distance to separation ratio. Longer focal
length lenses allow us to move further back and thus increase this ratio.

As the lens separation increases, for a given camera to subject distance, so
does the "stereo bite".

100mm separation with 35mm lenses can be ideal for most scenic shots where
the nearest object is 3m or more away. A similar shot with the closest
object 6m away would require at least 150mm of lens separation to have
sufficient "stereo bite".

The optimal separation for many award winning action slides is often about
150mm.  Due to the distance from the subject and the focal length of lenses
the scale of these pictures are generally well within the acceptable range.

Download the article referred to above and read my complete article and
Steve Spicer's more  technically correct response.

A sample copy of '3d Window' can be downloaded free from:
http://www.sscc.asn.au/sscc/index.htm  If you leave your name and email
address when you download the sample issue you will receive an offer of a
follow up issue.

Ray Moxom