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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