Re: bi-ocular devices

[P3D Peter Homer <P.J.Homer@xxxxxxxxxxxxxxxxx>]

William Carter writes " A single lens 3-d miroscope with an objective N.A
of 1.00,renders a view that's 90 degrees to each side of a subject ! Man
that's 3-D And there's ne eye strain. It all looks very "normal" (unless
you that some crystal cube shouldn' t look like the world Trade Center).
   But is he being serious ? a N.A. (Numerical Aperture) of 1.00 would give
a view 90 degrees to each side of the subject as N.A. is the sine of half
the angle of acceptance( which if it is 180 degrees would give 90 degrees
the sine of which is 1) x the refractive index which for air is also 1
giving a total of 1. This is the sort of thing lens designers are striving
for to give the maximum resolution for a microscope but I did not think it
had been achieved for an objective. To accept an angle of 90 degrees either
side of the object I.E 180 degrees the first lens would have to be a
meniscus curving around the object with either no cover slip or a circular
one small enough to fit inside the lens curvature. Leitz once made a dark
groung reflecting condenser somewhat like this but not an objective. A
N.A. of 1.00 is the theoretical maximum for a "dry" condenser and the
highest of these at X40 magnification would come closest to this figure.
With a X100 oil immersion higher figures than 1.00 are possible but this is
largely because of the higher refractive index (1.515) which is the same as
the glass lenses so that the angle of the rays is not reduced by
refraction.
 The lens is also closer still and can accept a still wider angle of rays
but not 90 degrees or an N.A. of 1.515 would be possible . In practice I
believe only something like 1.4 is attainable the best we have at work is
1.3.
 What William Carter describes sound like distortion due to a wide angle of
difference between the views but a 90 degree view either side of a cube I
would not expect to be distorted or stereo for that matter!. My own
experience of single lens 3-D microscopes is that the stereo becomes less
noticeable at high powers perhaps due to the poor DOF another consequence
presumably of the high angular aperture due to extreme close up . This was
apparent even when I made some measurements with a graticule.
                                             P.J.Homer



------------------------------