G. Parenti: Future 
of the telescopic 
photoprinter-rectifier. 
(Publ. IP 2) 
encore beaucoup plus difficile d’y satisfaire, puisque la plaque doit être éclairée 
par transparence. 
Il est nécessaire d’abroger le débat. Je regrette de ne pouvoir redonner la parole 
à M. Thiriar pour qu’il réponde à des questions telles que celles-ci: 
— pourquoi souhaite-t-il des déformations cylindriques plutôt que de révo 
lution autour de l’axe de la chambre? 
— pourquoi recherche-t-il systématiquement à faire des plaques concaves et 
préconise-t-il d’émulsionner la face concave alors que. je crois qu’en général 
l’émulsionnage a une tendance à augmenter la concavité en provoquant un re 
trait de la gélatine au séchage? Espérons qu’on pourra revenir sur cette question 
à notre dernière session. Pour ma part, j’attire une fois de plus l’attention sur 
la permanence de la forme géométrique de la surface sur laquelle on enregistre 
la photographie du terrain et sur l’ignorance dans laquelle nous sommes le plus 
souvent de la forme de cette surface au moment de la prise de vues. J’arrête la 
discussion et donne la parole au Dr. Parenti. 
Mr. Cruset says that it does not seem possible to retain Mr. Thiriar’s suggestion, that a concave 
plate should be flattened out by a pressure being brought on it inside the camera. The same 
would be necessary, and even more difficult to bring about, in the plotting-machine, where the 
plate is illuminated by transparence. Unfortunately, shortage of time available prevented Mr. 
Thiriar from answering the following questions from Mr. Cruset: — why cylindrical deformations 
should be considered more desirable than revolution deformations around the axis of the camera? 
— why should plates be coated systematically on the concave face, while it is generally believed 
that emulsioning tends to increase concavity, because of the shrinkage of gelatine? Attention is 
drawn again, by M. Cruset, to a permanent geometrical shape of the surface on which a photo 
graph of the terrain is registered and the fact that one does not know, generally, what shape this 
surface had at the time the photographs were taken. 
G. Parenti: Future of the telescopic photoprinterrectifier. 
In 1936—1937 Nistri studied and realized a telescopic photoreducer that was 
based on the Porro principle with the scope of obtaining, from aerophoto- 
grammetric plates, the plates to be used in his Multiplex which had been 
presented at the Paris Congress a few months before. 
The essential characteristic of this instrument, as is known, was that of its 
being formed by two superimposed cameras, the upper one which was fitted 
with a lens that was the same as the take lens, and suitably illuminated from 
the plate side, was the projection camera, while the lower camera was fitted 
with translations so as to make up for the defect of pupil coincidence, and was 
formed by a lens similar to the projection lens of the Multiplex and calculated 
so that the distortion difference between the two lenses would be negligible. 
It is evident that with this procedure any take camera distortion whatever is 
totally compensated. 
The new technique of nadir gyroscopic recording, which permits to rapidly 
individualize and mark the position of the nadir point on the negative film, has 
suggested to reconsider and re-elaborate the described instrumentation by 
profiting from the new possibilities that this technique offers. In fact, by setting 
up the projection camera on a universal joint system, there results the possibility 
of imposing the values of co and cp to it, with the approximation allowed by the 
gyroscopic system of recording and thereby to re-establish the orientation of the 
take bundle, prescinding from K; therefore to obtain a »rectified» photogram 
in the lower camera. 
The setting of the co and cp angles can be made by individually deducing them 
from the position of the respective pointers, and if the nadir point has been 
pricked, the position can be refined by means of an optical checking system 
that is brought in correspondence with the projection lens and which is then 
removed before starting the exposure. 
The use of the photogram on film photoprinter-rectifier has made it necessary 
to solve the problem of flattening the film. The usual perforated plate pneuma 
tic systems evidently cannot be applied because the plate itself must be trans- 
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