Busch Vademecum & Casket Meniscus Lenses
The information below is first hand “Source Information” from 1902 on Casket lenses Including the Busch Vademecum and many of the other period casket sets of the era. The information below is word for word as written in the original text with the exception of several spelling corrections.
Please also note that while these lenses can have a large aperture if fitted in a shutter or larger tube, f:16 is the largest stop that these lenses should be shot at. That is unless your desire is to have the image deterioration that comes with shooting these lenses at larger apertures. The original images below were approx. 3x4 inches in size (dot matrix / not plates).
I hope you enjoy this rare hundred year old treasure: Tim
 The spectacle lens is usually about 1 1/2 in. in diameter, and can be obtained of any focal length from 6 ins. upwards. It is used with a fairly large stop (f 16) and allowance made for the fact that the image seen sharply focused on the ground glass is not rendered sharply by the plate. This allowance is made in several ways:
(1) The camera is racked in a little after the picture has been focused. The exact (distance is 1/40 of the focal extensions when the lens is focused on objects a long way off.
(2) A much more convenient method is that of Robert H.Bow. When focusing, a weak and thin convex lens is inserted behind the spectacle lens. The strength of this supplementary lens is such that it reduces the focal length of the spectacle lens by the 1/40 mentioned above. Before exposing, it is removed and the plate is of course in the right position for a sharp image. The focal length of this supplementary lens is usually forty-five to fifty times that of the lens to be corrected.
" Leafless Trees." By W. Thomas. Taken with a Busch casket Jens at f40.
When isochromatic plates and a yellow screen are used, this correction is not necessary. In fact, with certain screens and plates it results in fuzzy images being obtained. In this case the simple plan of exposure after focusing without any correction can be followed with satisfactory results.
In portraiture, copying, etc., the correction mentioned above becomes more than one fortieth of the actual focal length, and when copying objects same size as the original (say a life-size head), the correction becomes as much as one twenty fifth. Various rules and tables have been published, but the following from The Photogram is perhaps the simplest. The first line gives the ratio of image to the original. The second gives the necessary corrections.
This percentage correction is on the actual, and not on the equivalent focus of the lens. For instance, with a lens of 12 ½ inch focus, the correction for distant objects (infinity) would be 2 per cent of 12½ inches or ¼ inch; while the correction for the same lens, when copying life-size, would be 4 per cent of 25 inch, or one inch.
" September." By W. Thomas. Taken with a Busch casket lens at t40.
The examples on pages 115 and 116 by W. Thomas show that sharp pictures can be obtained (fig. 114) 'with the spectacle lens as well as the diffusion of focus seen ill fig. 115. In portraiture this diffusion is an advantage, as witness the bit of work by Miss Evelyn Boden (fig. 116).
[3J Spectacle Lenses in Caskets - Uncorrected or spectacle lenses are put up by several makers in very convenient casket forms. A set of lenses, each in its own brass cell, is supplied with a mount into which they are screwed. The range of focal lengths is very great, as will be seen from the table on next page issued with the Busch casket of seven lenses.
Taken with a 12-inch Dolland Monocle at full apertnre.
By Miss Evelyn Boden.
One of the disadvantages of caskets is, that when lenses of different foci are used in the same mount, the position of the diaphragm is at its best for one focus only. When only a few (say three) different foci are needed this difficulty may be easily overcome, as it has been in the case of Wray's casket. This had a great vogue at one time, and it is difficult to account for the change of fashion--it is certainly no fault of the apparatus-which has led to its being practically neglected.
Click on thumbnail image for full larger view
The lens-tube, of brass or aluminum, extends telescopically by a single slide, and is closed when using the shortest focus lens, partly extended for the medium, and fully extended for the long focus. Three uncorrected (" spectacle") lenses are supplied, one in the back of the mount, the others in a leather case, and the diaphragm is an iris, marked with a separate set of / numbers for each lens. The half-plate set has lenses of 6&-inch, 9-inch, and 12-inch focus.
The general conclusion on these caskets is that they need a little more care in use, and cannot of course give the supreme results in the way of definition rendered by more expensive lenses. But they are extremely useful, and we should advise every man who is beginning photography, or who has one lens and wishes to buy another, to take one of these caskets instead of a single lens. He will eventually want more perfect tools, but, meanwhile, he will gain a knowledge of the use of lenses generally, which is impossible to the man who only uses complete lenses, and he will gain a versatility in selecting subjects, and in arranging his subject within the space of the plate, that will be in valuable in picture-making. The price of a casket of spectacle lens varies from £1 5s. to £3 3s.
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