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TL, Kiev 80 and Lubitiel. It seems to be difficult 
to fasten the reseau plate in the Kiev 80 camera 
body, because of its fiducial frames exchangeable 
together with film magazines (Kiev is similar to 
Hasselblad). On the other hand the simple and 
rather inexpensive Lubitiel (the two objective still 
6x6 camera, no exchangeable optics) seemed to be 
too simple for our first approach to the adaptation 
problem. So we decided finally to choose the Pen- 
tacon Six TL camera (fig.1), provided with exchan- 
geable objectives, build-in exposure mater, and a 
focal-plane shutter of wide range of exposure times. 
Also very important was the conclusion of the camera 
inspection which assured us that it will be compara- 
tively easy to build in a reseau glass plate. 
The insertion of the glass plate between objective 
and camera fiducial plane causes changes of the 
image distortion and image resolution. The resultant 
image distortion after adaptation will consist of the 
objective distortion and of the optical flat glass 
distortion. The optical flat glass causes always dis- 
tortion of equal sign (displacements toward the 
image center), while the sign of the objective dis- 
tortion can vary along the image radius.The resultant 
image distortion effected by this two factors can 
decrease or increase in comparison with distortion 
caused by the objective only. 
The quality (resolution) of image created in the 
camera depends on the objective aberrations and 
the aberrations of the flat glass inserted to camera 
in front of the fiducial plane. The flat glass plate 
will generate such aberrations, as astigmation or the 
curvature of the image field. So the resultant image 
resolution can be different than that of objective 
alone. So, the insertion of the flat glass plate to 
the camera optical system can cause change of the 
distortion and usually decrease of the resolution 
power. In exchange we are gaining minimalisation 
of errors caused uy film nonflattness and by the 
film shrinkage (here must be used the reseau grid). 
Better film flatness is gained by pressing it to the 
flat glass plate. On the film which fits better the 
fiducial plane the sharper image can be recorded. 
The flat glass plate must first be attached to a 
special metal frame-mount, and glass in the mount 
can then be inserted and fixed to the camera body 
(to fiducial frame). The frame-mount with the flat 
glass plate must be adjustable to fulfill the condition 
of its perpendicularity to objective axis. One must 
consider that the flat glass plate inserted to a camera 
can cause a change of the zero position of the 
distance scale on the objective. In such case also 
inequality of distances from objective to fiducial 
plane and to the ground glass of the view finder 
will appear. 
And again, there appears the problem of physical 
room for the glass. Even very thin glassplate captures 
some space inside of camera. It is comparatively 
easy to fix the glass plate atop of the original fiducial 
frame of the camera, but this will reduce the space 
reserved for film on the back of the camera. Since 
the film must shift smoothly in the camera (bigger 
tight of the film in the camera can cause unpre- 
dictable deformations of recorded picture), the ne- 
cessity of constructional changes of the back camera 
cover appears. 
2.2. The reseau plate 
In 6x6 medium format cameras there is variety of 
designs of shape and size of reseau grid. For example 
in the Hasselblad MK 70 camera there is 25 crosses 
which create regular 10mmx 10mm net (the crosses 
cover only picture of 40mmx40mm size); in Rol- 
leiflex SLX Reseau there is reseau grid of 121 
crosses (5x5mm grid covering 50x50mm picture 
area) (Wester-Ebbinghaus,1983). 
  
  
L—————— 50 mm : ZZ 
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Fig.2 The reseau grid 
We decided that 5x5mm grid is too dens, be cause 
crosses can interfere with the image contents making 
it less clearly readable; it is also to difficult to 
survey so many crosses. In the opinion of the reseau 
camera users, rather only generalized grid is 
measured in practice (Meid & Hasch, 1984), and 
no great loss of accuracy is noted. For our camera 
we designed a grid of 49 crosses (fig.2) which covers 
50x50mm area. Our reseau grid consist of 16 squares 
10x10mm and additionally each net line is 5mm 
extended at the edges what densifies the grid at 
the picture limits, where image errors can be biggest. 
Reseau crosses are of 1x1mm size (only central