This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Tessar Lens, Series I-C. It has been found possible to increase the aperture without sacrificing brilliancy, definition and flatness of field, and the result is a new lens of the Tessar type, having a speed of f.4.5; that is to say, the new lens is twice as fast as the Tessar f.6.3, which has been so favorably received and is so well known. This lens is known as the Series I-C, and is shown in Illustration No. 54.
736. This Gain in Speed is a most important consideration to the newspaper photographer and others engaged in speed work, and makes it possible to secure pictures of rapidly moving objects with a sharpness of definition hitherto unattainable. This speed of f.4.5 is not restricted to the smaller sizes, but extends to all the lenses up to the largest foci.
737. Illumination and definition are not only better in the center than in other lenses, but extend more evenly over the entire field. Its optical corrections are so exceptionally good as to render it well adapted for the use of process workers.
739. The Bausch & Lomb-Zeiss Protar Lens is made in various series and embraces a great variety of speeds, ranging from f.8 to f.18. The Series II has for its chief aim a lens combining rapidity and great extent of field. The speed is f.8, which is fast enough for ordinary instanta-
TESSAR Actual Size. Illustration No. 53 See Paragraph No. 723. BAUSCH & LOMB LENSES.
TESSAR Actual Size Illustration No. 54 See Paragraph No. 735.
PROTAR Actual Size. Illustration No. 55 See Paragraph No. 741. BAUSCH & LOMB LENSES.
PROTAR Actual Size. Illustration No. 57 See Paragraph No. 748.
PLASTIGMAT. Actual Size. Illustration No. 62. See Paragraph No. 760.
RAPID UNIVERSAL. Actual Size. Illustration No. 66 See Paragraph No. 762 neous work. The angle of view is 75 degrees, of which 60 degrees are utilized on the various plates. The definition which the lens produces is excellent, for with it detail is obtained with faultless exactness. This lens was primarily intended for hand camera work, and is suitable for this work because of its neat and compact mounting, short focus, applicability of the shutters and excellent optical qualities. This lens is an unsymmetrical doublet, neither system of which can be used singly. This lens should always be selected for hand cameras when symmetrical construction is not desired and when a medium wide angle lens is considered necessary. Its focus is shorter than that of other lenses, while at the same time the covering capacity is quite equal to that of the rest.
741. The Series IV. of the Protar Lens works with a speed of f.12.5. The angle of view of this lens is 100 degrees in the six smaller sizes, and 85 degrees in the larger. The actual size of the 5 x 8 lens is illustrated in Illustration No. 55, while the cross-sectional view of the optical construction is shown in Illustration No. 56. This lens combines the two
Illustration No. 56 important qualifications: That of wide angle aperture and speed of unusual extent. It may be classed as a medium angle lens, and is listed as such, giving sharp, well covered pictures, free from the ordinary distorted edges, a very important feature for a lens of this character, especially for outdoor Architectural Photography. Its use as an extreme wide-angle, however, is not precluded if the next smaller lens to the one listed is selected, or a given lens is used on the next size plate. Its speed is such that it will give instantaneous exposure, and it is particularly valuable for flashlight exposures of large gatherings.
742. Series V. is intended for the most exacting wide angle photography. For this purpose it is one of the most desirable lenses made, and should be selected whenever an extreme wide angle lens is required, as in architectural and interior work. The anastigmat and spherical corrections are practically perfect. The images produced by this lens are entirely free from distortion from center to margin of plate, even with the most extreme angle.
743. The larger sizes are designed specially for copying, and for that purpose produce unexcelled quality of work. The angle of view is 110 degrees in size up to, and including, No. 7A. Above that number the full angle is 90 degrees. The speed of this lens is f/18, which is sufficient for most outdoor instantaneous work in sunlight.
744. In Illustration No. 57 is shown the Bausch & Lomb-Zeiss Protar, Series VII A, which lens is the result of efforts made to construct objectives of universal application. This lens is composed of two Series VII. lens, each system of which can be used separately, and when so used the speed is f/12.5. When the combination of systems is employed greater speed and greater effective angle are secured, the speed being f/6.3.
Illustration No. 58
745. When the two single anastigmats have different focal lengths, or foci, the lens is convertible into three individual, perfectly corrected anastigmat objectives in one.
Illustrations No. 59 and 60 - See Paragraphs No. 753 and 754
Belt." The upper of these two pictures was made with Series VIIA, No. 17, with 12 inch focus. The lower picture was made with the rear combination of the same lens.
Illustration No. 61 Relative size of image in a picture made with a No. 8 Series VIIA (1) Made with doublet. (2) With rear combination. (3) With front combination. See Paragraph No. 755.
When the single elements have the same foci, two separate objectives may be formed.
746. By the addition of one single anastigmat, six lenses, three single and three doublet are obtained, each with different angle, focus, and covering power.
747. The addition of two single anastigmats gives ten lenses, four single and six doublet.
748. A general exterior view of this lens mounting is shown in Illustration No. 57, while Illustration No. 58 shows the optical construction when the two single anastigmats which make up the combined lens are of different foci.
749. The photographer possessing this convertible lens is able to meet with practically all conditions of universal photography, the single elements being used for landscape work and other purposes where long focus, medium speed, or low or medium angle are sufficient. The doublet gives an extra rapid lens of wide angle, suitable for fast instantaneous work, most difficult architectural subjects, and any situation where speed, angle, covering power, depth of focus and brilliancy are required.
750. The average angle of view utilized on the different plates is about 55 degrees.
751. When the foci of the two single elements are the same the speed is f/6.3; when different, f/7 or f/7.7.
752. For hand cameras these lenses stand at the head of the list, both in optical qualities and in their adaptability to the limited space allowed for the lens. In selecting the lens be sure that the back focus of no combination is longer than the greatest extension of which your camera bellows is capable.
753. In Illustration No. 59 we illustrate the use of the Series VII A, No. 17, with 12 inch focus. The picture shows the official test of high-pressure water mains traversing the Philadelphia "fire belt."
754. Illustration No. 60 was made with the rear combination of the same lens.
755. Illustration No. 61 illustrates the relative size of image in pictures made with a No. 8 Series VII A Protar lens; (No. 1) made with doublet; (No. 2) with rear combination; (No. 3) with front combination.
756. Bausch & Lomb Plastigmat Lens. - This is a strictly anastigmat lens. We have accomplished the purpose so completely that this lens is giving an exceptionally greet amount of satisfaction to all its users. The lens has great speed, crisp definition over a large circle, wonderful covering power and even illumination. It is a symmetrical lens, the front and rear combinations being composed of four lenses each. The glass used is very transparent and absolutely permanent. The lens works with a speed of f/6.8.
757. The separate systems show truly remarkable covering power. The rear combination can be used at a speed of f/13.5; the focal length being nearly twice that of the doublet, and therefore the images produced are twice the size at the same distance, or the same size at twice the distance.
758. Excellent perspectives can be obtained with these lenses, because the focus is longer for the various plates than is usual in other anastigmats.
759. This lens is particularly well adapted for use with the hand camera, because of its excellent optical properties, light weight, compact form, and the applicability of shutters between the lens combination. It is an ideal lens for general photography, and we can recommend it in every respect when a lens of the highest optical excellence is desired.
Illustration No. 63
760. We show the actual size of the 4 x 5 Plastigmat lens in Illustration No. 62, and in Illustration No. 63 is shown a sectional view of the optical construction.
761. Illustration No. 64 is a photograph of Mount Shasta, at a distance of seven miles, made with the Doublet Plastigmat, by H. H. Derr. In Illustration No. 65 is shown Mount Shasta from the same point, the negative having been made with the single combination of the Plastigmat lens.