The Photo-Miniature Volume 8 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 Excerpt: ... length of bellows. 4. What is the magnification possible with any given length of bellows? In this case the formula is--b m = (-1. f" For example, with a negative lens of f, equal to 3 inches, and a bellows extension of 12 inches, what enlargement can be secured? 12 m = 1-1 = 5 diameters. 3 5. What size plate can be covered with any combination at any bellows extension? b(a'f" ] a"P) f" 1 f--f" j For example, with a positive lens of 7-inch focus and 1-inch aperture, and a negative lens of 3-inch focus and also 1-inch aperture, and a bellows length of 12 inches, what is the diagonal of the plate covered? 12(1X3 + 1X7) () d =--= +--f = 10 inches. 3 I 7--3 J I 4 J This is obviously ample allowance for 85x7 plate. 6. What is the increase of exposure in any case? The rule is, ascertain the correct exposure in the case at hand for the positive used alone, multiply this figure by the square of the magnification; t = m times exposure for positive lens alone. These formula; are not so forbidding as they may look to the non-mathematical eye; they are merely so many simple ways of arriving at the data the telephotographer is sure to want in the course of his work, and they are inserted in this monograph because we think the reader will very often wish to consult them. Getting to practical work, the first Work steP t'le te'ePnotograPner must take is to provide a perfectly rigid stand for holding the camera and lens. He will make most of his exposures by time, with a small stop, so it is important that he should work from a firm base, not easily affected by tremor or vibration. Some photographers use a second stand for supporting the lens end of the outfit; others an arm which extends from the stand to the base of the camera; others a steel or ...