Optics of photography : on a new process for equalizing the definition of all the planes of a solid figure represented in a photographic picture / by A. Claudet.

  • Claudet, A. (Antoine), 1797-1867.
Date:
[1866?]
Catalogue details

Licence: Public Domain Mark

Credit: Optics of photography : on a new process for equalizing the definition of all the planes of a solid figure represented in a photographic picture / by A. Claudet. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    which remains fixed during the adaptation of the focus to the distance of every plane by means of a gradual movement com- municated to the back lens during the sitting. Ihe inspection of the apparatus, which I submit to the Meeting, will enable any visitor interested in the question to understand its action. It is marvellous when we reflect that there is nothing to wish for in the shape of contrivances having for their object the percep- tion of vision, and that from time to time man invents, or thinks lie invents, what nature had done in the most perfect manner, ihe eye is supplied with a lens in the same way as the camera obscura; the retina is the screen on which, like the ground glass of the camera, the light reflected by all the natural objects form their image. By various humours through which the light is refracted, the Spherical aberration is corrected and the most perfect achro- matisin is produced; the eye is endowed with muscles which enable it to alter the focal distance of the lens according to the various distances of the objects. Optics is able to imitate all these beautiful contrivances except the last, which is available only on account of the way in which we exercise the perception of vision. We see at once only a very small part of the image— that part which is projected on the centre of the retina; and the eye can adapt its focus to the distance of that part, and, as ra- pidly as thought, when directing its attention to another part it adapts its focus to that new distance. Therefore it matters not whether the other parts are in focus; we have only the perception of what we want to see, and, by the proper adaptation, that sensa- tion conveys to our mind only a well-defined image. It cannot be so with the camera obscura, because, the photographic image produced by it being at once permanently fixed entire by the same exposure, we cannot change it in changing the focus; the only thing we can do is to impress a stronger image on a fainter image. The artificial optical instrument being destitute of a self-acting changing adaptation to the focus of all the other planes, can represent only one plane in focus-, but if it had that adaptation, the surface receiving the impression of the image in a permanent manner (not like the retina, which does not retain the impression), that impression would consist of a number of images superposed one upon another. For this reason nobody would ever have thought of proposing to employ a lens which, moving during the exposure, would adapt itself consecutively to the foci of all the other planes of the image. But from the fact that the eye can easily and usefully alter its focus according to the distance of the plane it wants to examine, and unconsciously dis- card the image of the other planes while they are out of focus, it is possible to learn what may be a very useful modification of the arti- ficial optical instrument called the camera obscura. If we cannot