Optical Projection Part 1: Projection of Lantern Slides

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Title: Optical Projection

Part 1: Projection of Lantern Slides

Author: Lewis Wright

Russell S. Wright

Release Date: October 31, 2010 [EBook #33899]

Language: English

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OPTICAL PROJECTION

A TREATISE ON THE USE OF THE LANTERN IN

EXHIBITION AND SCIENTIFIC DEMONSTRATION

BY

LEWIS WRIGHT

AUTHOR OF 'LIGHT: A COURSE OF EXPERIMENTAL OPTICS'

5TH EDITION

RE-WRITTEN AND BROUGHT UP-TO-DATE BY

RUSSELL S. WRIGHT, M.I.E.E.

IN TWO PARTS

PART I

THE PROJECTION OF LANTERN SLIDES

WITH ILLUSTRATIONS

L O N G M A N S ,   G R E E N ,   A N D   C O.

39 PATERNOSTER ROW, LONDON, E.C.

FOURTH AVENUE & 30TH STREET, NEW YORK

BOMBAY, CALCUTTA, AND MADRAS

1920

(A l l   r i g h t s   r e s e r v e d)

PREFACE

TO

THE FIFTH EDITION

The first edition of this work was written by my father, the late Mr. Lewis Wright, and was published in 1890.

The reception that it received testified to the fact that it met a long-felt want, and successive editions were published in 1895, 1901, and 1906.

My father, unfortunately, met his death in a railway accident in 1905, and the corrections and additions to the last edition, which had been to a certain extent prepared by him, were completed and written by myself, and the work as published then was again reprinted in 1911.

As the original text is now thirty years old, it has seemed better entirely to re-write the whole book rather than make fresh revisions, the more so as the last ten years have seen great advances in the science of Lantern Projection, and especially in the developments of Acetylene and Electric Lighting.

It has also seemed best at the present juncture to issue the book in two parts, the first dealing with the Projection of Lantern Slides only, and the second with the Demonstration of Opaque and Microscopic Objects, Scientific Phenomena and accessory apparatus, including Cinematograph Projection.

It must of necessity be many months before this second volume can be produced, for the simple reason that Optical Instrument Makers have as yet hardly had time to turn round after the war and produce their new models, and therefore any such book written now could do little more than describe apparatus that was on the market prior to 1914.

The present work, therefore, deals solely with the exhibition of Lantern Slides in the Optical Lantern, and as such I trust will be found of value to Schoolmasters, Social Workers, Lecturers, and, in fact, to all who use the lantern as a means of illustration.

RUSSELL S. WRIGHT.

January 1920.

CONTENTS

ILLUSTRATIONS

OPTICAL PROJECTION

A TREATISE ON THE USE OF THE OPTICAL LANTERN

CHAPTER I

INTRODUCTORY

Lantern Projection, as commonly understood, may be broadly subdivided into two branches: (A) The Projection of Lantern Slides, and (B) The Projection of Scientific Phenomena, Opaque Objects, Microscopic Specimens, &c., usually referred to broadly under the heading of 'Scientific Demonstration.'

To these two classes may perhaps now be added a third, viz. The Projection of So-called Living Pictures, or, in other words, the Cinematograph. In the earlier editions of this work both A and B were dealt with in the same volume, but, as there are thousands who require to use a lantern for the demonstration of lantern slides only, and who have no interest or concern with Science Projection, it has seemed to the writer that the work might, with advantage, be divided into two portions, Vol. I. dealing with slides only, and Vol. II. with the various adaptations of the science lantern. This present book therefore only deals with the exhibition of lantern slides, and as such it will, I trust, be found to be of real assistance to the ordinary user of the optical lantern, including clergymen, schoolmasters, army and cadet officers, and others who require advice and instruction in the purchase or use of a lantern.

The essential parts of a lantern are: (a) A slide-holder or carrier to hold the slide; (b) a lens to 'focus' it on the screen; (c) a condenser to converge the light upon slide and lens; (d) a source of light or radiant to provide the necessary illumination; and (e) a body or framework to hold the whole together. All possible variations in choice of a suitable lantern relate to one or another of the above parts, and will be treated of in turn; but, fortunately, we have this all-important simplification that every ordinary English lantern slide is the same standard size, viz. 3¼ inches square. Some Continental and American slides differ in one dimension from the above, but not enough to cause any serious difficulty, and the convenient English standard is being gradually adopted throughout the world.

The varieties of slide-holders or carriers are therefore comparatively few and are chiefly concerned with the question of rapidly and easily changing the slides. The choice of a focussing lens or objective is mainly a matter of the size of picture required, and the most convenient distance from the screen for the lantern to be placed. Variations in condensers, which are comparatively small, are usually only a matter of conforming these with the size or type of objective to be used, and should be left to the manufacturer's judgment. The question of a suitable radiant is partly a matter of the amount of illumination required, and partly that of the practical possibilities; for example, if electric current is available some form of electric light is usually the most convenient, as well as the least expensive, but where this is not the case, paraffin-oil, methylated spirit, incandescent gas, acetylene, limelight, &c., are alternatives which all have their uses and must be considered on their own merits.

Sometimes, as for example in the case of a travelling lecturer, a lantern is required fitted with a range of lenses for halls of different size, and also with a variety of illuminants, and this in most lanterns can be easily provided for.

The body is usually a matter of taste and price only, and may range from