Just another dome story!
Hi eveready, following a tread on dome optic/clown fish in the gallery section, me and CeeDave aka Chris came up with this diagram. His textual approach to this complex phenomenom is one of the best, so I have contributed my illustration talent to his talentuous text. hope you enjoy,
Capital letters = camera/lens
Small letters = housing/port
( L ) : film plane
( F ) : lens mount flange
( P ) : entrance pupil
These should be made available
by camera manufacturer.
( f ) : port flange
( e ) : extension flange
( c ) : center of curvature of the dome
( d ) : location of dome surface
( r ) : radius of sphere that dome is based on, ( r=cd )
All thas is needed from housing manufacturer is
( r ), ( fe ), ( Ff ), and ( ed ). All known from
manufacturer or easily measured.
We want the distance from dome surface to
entrance pupil, ( Pd), to be the same as the
distance of the center of the dome to the
surface, ( cd ). ( cd=dome radius ), which
is ½ the diameter of the dome ONLY in
hemispherical dome. Also( c ) is in the plane
of the back of the dome only in the case of
hemispherical dome.
From the Diagram:
The Camera flange to dome surface distance is ( Fd = Ff + fe +ed )
The camera flange-pupil distance may be computed using the film
plane datum is ( FP = LP- LF ).
The Pupil to dome surface is ( Pd = Fd - FP )
If the dome is in the wrong position, rays do not
pass through the dome to the lens perpendicular
to the dome. This causes refraction, and thus
chromatic aberration and blurring...the effect is
most noticable at the edges of the dome, where
the angle is furthest from perpendicular.
Also, larger dome have more gently curved
image planes and require lower diopters,if any,
for focusing; this is a lesser concern with
fisheye lenses than with rectilinear lens.
Illustration by Jean Bruneau a.k.a Viz’art
Text by Chris White a.k.a CeeDave
