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The photographic news
- Bandzählung
- 13.1869
- Erscheinungsdatum
- 1869
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 540, January 8, 1869
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The photographic news
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Band 13.1869
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cally in the plane of the eye, place yourself at arm’s length from the mirror. The reflection of the rule will appear to be of exactly half the length of that of the cardboard, or of the cardboard itself, which is the same thing. As long as the rule is kept vertical, and in the same plane as the eye, you may either approach or retire from the mirror, the reflection of the rule will always appear to be of exactly half the length of the cardboard. Experiment 4.—Fix some object, which should not be less than 3 feet long, in an exactly upright position at any given distance from a mirror, and retire till the eye is at exactly the same distance from the object as the object is from the mirror. The reflection of the object will appear to be one-third the height of the object itself. Corollary B.—In Experiment 3 we saw that the apparent height of the reflection of the rule was half that of the cardboard. But, by corollary A, that is the height that the rule itself would appear if it were placed as far behind the cardboard (or mirror) as it is in front of it. In Experi ment 4, as the distance of the object from the eye may be any thing, let us, for purposes of calculation, call it n feet. It will also be n feet from the mirror. The apparent height of the reflection is one-third that of the object, or the same height as the object itself would appear if it were at 3n feet from the eye, or n feet behind the mirror. It is evident that if the mirror is vertical, but the objects inclined, or vice versa, the reflections will be foreshortened. We are quite aware that to give a rigid experimental proof of our propositions would require an infinite number of experiments, but we considered that these were a sufficient illus tration of their truth; and they may be easily confirmed by anyone who will take the trouble to measure the distances with accuracy, and to place all the objects exactly vertical. Want of sufficient attention to these points seems to have led Dr. Anthony to an erroneous conclusion on a point which does not seem to have been subsequently referred to, and which, as he has drawn from it an analogous conclu sion with regard to lenses, seems to require some notice. Wo will discuss the question of the images formed by lenses presently ; but in the meantime, knowing the laws which govern the apparent size of reflections, let us try to apply them to the instance before us. In his letter in your paper of October 9th, he says: “ On a slip of glass gum some bars of paper at 2 inches apart; stand in front of a mirror (say at 20 feet off it), place the glass with the bars in the plane of your face, and the face and head will appear to fill five of the spaces between the bars; hold the glass 2 feet in front of you, and as you look through it at the reflection in the mirror you will find that your oval of head and face will only till four of the spaces. Now, if you go forward to a distance of 4 feet from the mirror, and you place the barred glass in the plane of your face, you will find the oval fill the five spaces as before; and if you advance the barred glass 2 feet, as you did in the former experiment, you will find, as you did before, that face and head will fill only the four spaces, so that the exaggeration of perspective would seem to be equal for all distances.” When Dr. Anthony says, “ Your oval of head and face only 7 fill four spaces,” he clearly means the reflection of the oval, but it is not equally clear whether he means four spaces of the glass itself, or of its reflection. Let us, therefore, test the correctness of this experiment on each supposition. Supposing, first, that we have to compare the glass itself with the reflection of the face in the mirror. The eye is at a distance of 2 feet from the glass, and of 20 feet from rhe mirror; the reflection of the face will, therefore, appear to be at 40 feet from the eye, or twenty times as far as the glass, so that instead of four spaces of glass being required to cover the reflection of your face, only a quarter of one would be needed. I conclude, therefore, that Dr. Anthony intended that the reflection of the glass should be compared with that of the face. In this case the reflection of the face will appear, as before, of the same size as if it were 40 feet distant, but that of the glass will appear to be at twice 18 feet (its distance from the mirror), plus 2 feet, its distance from the eye, or 38 feet. That is to say, that the reflection of the glass being called 20, that of the face would be 19, not 20 and 16, or 5 and 4, as Dr. Anthony noted them. Let us examine in the same way his second experiment. The face being at 4 feet and the glass at 2 feet from the mirror, the reflection of the former will appear to be at 8 feet and that of the latter at 6 feet from the eye ; and their pro- portionate sizes 3 and 4 : a very different proportion from l9 and 20, and not agreeing either with Dr. Anthony’s ob servation, which was again 4 and 5. I therefore conclude that he is in error in stating that what he calls “ the exaggeration of perspective ” is the same for all distances, and that his further conclusions, applied by analogy to lenses, are not proved. (To be continued.) orresyonente. PHOTOGRAPHER’S RELIEF FUND. Mx DEAR Sib,—As the question of a Photographer’s Relief Fund is now at issue, and discussion is invited upon the subject, I beg leave to say a few words. No one will doubt that a fund for the benefit or reward of the destitute or meritorious amongst photographers would be a great boon, and the question naturally arises, that in case such a fund should be obtained: Who ought to be the proper per sons to benefit by it, and by what process their eligibility is to be tested ? I see various opinions have been offered. For my part, I can see no better or fairer tests than those of the possession of a practical knowledge of our art, joined to a satisfactory proof that it has been followed as a profession. The submitting to and passing such an examination ought surely to be convincing to the most cautious. As regards any other sources of the income of such a person we have nothing to do, provided that photography has been the staple, and not merely the plaything or addition. I should be sorry to consider any one the worse photographer who, finding that his returns were decreasing from unfair compe tition, or any other cause, seeks to maintain an honest and respectable position by employing his otherwise useless leisure and capital in other directions. This is not the person who would willingly seek relief from any fund, and only in case of unforeseen and dire distress. I hardly think that your readers would, from such a cause, consider him disqualified for the reception of their benevolence. Amongst a very large connection of the profession, I hardly know of one photographer whb practises the art per se, and believe that in every case they have other dealings, more or less, besides photography. Although I should ever regret that any word of mine should appear antagonistic to so good a purpose, still I think that the title Relief Fund smacks a little of the work house. “ A rose by any other name may smell as sweet.” So it may ; but I should rather see our art and its professors increasing in dignity in the world’s estimation than the other way. Could not the same object be obtained in a more legitimate manner? About four years since I laid before your readers the idea of a photographic college, or society, on a similar plan to that of the Pharmaceutical, the eligibility of members to be tested by examination, and diplomas granted, a scale of fees to be charged, and a moderate annual subscription required; the surplus fund, after paying expenses, to be employed in charitable and other purposes, under the control of a council. I think it would have been better for the art and its professors had tome such society then been formed. Why not do it at once ? The kind of assistance already given and promised would be available, and need not be perverted from its in tended application. As there must be some test of eligi bility, the difference will mainly consist in the society being made a permanant institution, having a far greater and
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