AT
[ME ILE MEE
cross is 2x2mm), the line sickness is 404m. The
reseau grid was recorded on the 1.6mm thick glass
and measured on the precise monocomparator (As-
corecord of Zeiss Jena) with the accuracy greater
than +1um.
23 Fitting up the reseau plate to the camera body
First of all we have to assume that the film active
surface will be flattened on the exterior surface
(surface with crosses marked on it) of the reseau
plate in the camera. To record the sharp image
existing in the camera fiducial plane, after inserting
glass plate between the objective and fiducial plane
one must shift fiducial plane away from the camera
objective on Al — (n-1)d/n (where: n - coefficient
of light refraction in the glass, d - thickness of the
glass plate). If it would be possible, no other adap-
tational changes in the camera would be necessary.
In our Pentacon-Six and for our 1.6mm thick glass
plate the above described Al value would be equal
to 0.5mm (Al=0.5mm for d=1.6mm, n=1.5). But
this means, that our glass plate should plunge into
the camera metal fiducial frame by 1.6-0.5 — 1.1mm,
what would involve a serious cutting of the very
delicate and precise metal fiducial frame of the
Pentacon Six camera. Therefore in our case the
reseau glass plate was fixed in the camera in the
most convenient position from the point of view of
mechanical camera reshaping (fig.3). This resulted
in the shift of the camera fiducial plane (exterior
plane of reseau plate) not by 0.5mm but by 1.2mm
away from the camera objective.
advisable solutions solution employed
b
= b
Alz 05mm | a | }
rd
ports = ..Mmmi*, * 6mm.
= zz E 6mm =
on . e t ccm
——————— a oi 7A
to objective to objective
Fig.3 Fitting up the reseau glass plate to the camera:
a) the camera original fiducial plane
b) the exterior surface of the reseau glass plate (on
which the reseau crosses are marked)
The reseau glass plate was glued to the special
metal frame. This metal frame was lain on 4 pins
of @ = 1.5mm which were screwed to the camera
metal fiducial frame (they can be regulated). Metal
frame with the reseau glass is fixed to the camera
body with 2 screws, what enables easy assemblage
and disassemblege. The 4 pins ensure the stable
position of the reseau plate in the camera and
make the adjustment possible.
2.4. The Further Camera Modifications.
The mechanical assemblage of the reseau glass plate
(1.6mm thick) to the camera body caused a shift
of the camera fiducial plane (exterior reseau plate
surface) by 1.2mm (fig.3) away from the objective,
instead of 0.5mm (due to the glass plate). This will
effect the position of the camera objective, which
must be shifted by 0.7mm towards the fiducial frame,
to enable the proper use of the distance scale
existing in the camera. This was achieved by shor-
tening (mechanical cutting by 0.7mm) of the metal
cylinder assembling the lenses. The change of the
objective position developed the need for adjustment
of the ground glass surface of the camera viewfinder.
It had to be shifted away from the camera body on
0.7mm (this was ackieved using a spacer washer).
In the Pentacon Six camera the film is pressed
against the fiducial frame using flat plate contact
spring, which is connected on the interior side of
the camera lid. The spring is pushing film con-
tinuously to the slide bearings on the camera fiducial
frame. The maximum distance available between
slide bearings and plate spring is around 1.5mm.
After the reseau glass plate has been assembled
this distance was reduced to 0.3mm, what is far too
little for the easy shifting of normal film. To prevent
the film deformations caused by too tight sliding,
the whole lid of the camera (together with the plate
spring) was displaced from the fiducial frame by
1.0mm (the hinges and the lock were offset on
1mm). To enable approximate exterior camera orien-
tation in the field a circular level was attached to
the camera body and a mark was introduced to the
field of view of the camera view finder (it points
out the direction of the camera axes).
3. THE ADAPTED RESEAU CAMERA
PHOTOGRAPHIC RESOLUTION
The examination of the camera photographic
resolution ranged over the pictures taken using:
non-adapted camera and camera with the 1.6mm
thick reseau plate, and using two objectives: normal
angle Biometar 2.8/80 (for the f-stops: 2.8, 8, 22)
and wide angle Flectogon 4/50 (for the f-stops:
4, 8, 22). Pictures made without and with the
reseau glass-plate were taken for this purpose on
the photographic glass-plates TO1 ORWO. The
greatest losses of the camera resolving power were
noticed at the biggest entrance pupils of the ob-
jective. For the normal-angle Biometar 2.8/80 at
the relative aperture 1:2.8 the resolution without
the reseau-glass was around 37 l/mm at the picture
centre and 24.6 mm at the picture edges. The
1.6mm reseau plate caused the drop of the resolution
by 9.5 l/mm in the middle of the image field and
by the 2.4 l/mm at the image field edges. Relatively