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We ended part two of this series with the Struss Pictorial Lens, first marketed in 1915.  World War I obviously caused a reduction in new lenses reaching the market between 1916 and 1919, but the 1920's saw a great number of new Soft Focus Lenses being introduced in the US and Europe.  In fact, more Soft Focus Lenses were introduced in the 1920's than any other decade. 

Companies large and small seized the opportunity to market a Soft Focus Lens or at least a lens or filter that featured a mode of diffusion.  By 1930, there were a significant number of Soft Focus Lenses available to the photographer for purchase.  While the pictorialist movement may have declined, there were more Soft Focus lenses available in catalogues than ever before.

In 1919, the Kalosat, the "Spectral Diffusion Lens", was produced by the Hanovia Chemical and Manufacturing Company.  The company's name later became the Hanovia Lens Laboratories,.

The American Cinematographer Magazine of June 1, 1922, wrote the following about the Kalosat; "A most unusual lens is the Kalosat, made by the Hanovia Chemical and Mfg. Co. The lens, which was suggested by Dr. T. W. Kilman and Dr. H. D'Arcy Power of San Francisco, is made of quartz. After a series of lengthy experiments, the Kalosat was finally produced in October, 1919, being constructed of synthetic quartz of the desired optical quality.

The quartz of which the Kalosat is constructed is transparent to all the valuable light rays of the spectrum, including the ultra-violet. This feature makes it a very fast lens.  The lens was originally devised for speed, which it has, but it is marketed as a soft focus lens, and must be judged from this standpoint. The softness is due to the overlapping of the central image by the marginal image of slight intensity, so the degree of diffusion may be regulated by the diaphragm. In this lens the focus must be adjusted at the aperture at which the lens is to be used, as the focus varies with the aperture. The actinic and visual images very nearly, but not quite, coincide. There is a difference of one four-hundredth of the focal length of the lens between the two, so, if so desired, the lens may be focused visually and then racked back that distance to obtain the greatest sharpness.

The distribution of the area of softness in this type of lens depends upon the relation of the curvature of the lens to the plate and field. If the convex side of the lens is toward the plate, the diffusion is evenly distributed, and no area is critically sharp. This is usually the right position for general use. If the lens is reversed, sharp definition in the center, and rapid shading off into a blurring at the edges is obtained, a sometimes valuable effect.

The combination in the Kalosat lens of a high refractive index with a wide range of spectral transmission, produces in the picture a spectral diffusion of unique quality. The result of this phenomenon is a soft focus effect of remarkable quality. The spectral diffusion secured, combines a sufficiency of definition with a softness that permits of very broad handling, a feature not usually found in other lenses.

The quartz lens transmits a much greater amount of actual light than glass lenses. This makes the lens of greater actual intensity than the normal F. would indicate. In a comparative spectrograph, a standard anastigmat does not register light beyond the (ultra-violet) line 365, while the Kalosat registers beyond the line 238.  Since this end of the spectrum is the actinic end, the value of the quartz light-transmission is very apparent."

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The Kalosat lens was made in two series; Series I had a speed of f/4.5, and Series II had a speed of f/6.3.  The Kalosat, like many other Soft Focus Lenses, were also sold for motion picture cameras.

The lenses are also marked on the barrel with letters (A to D) to denote lens size.  See Kalosat brochure page below.

In 1921, Gundlach-Manhattan Optical Co. brought the Equal Diffusion Portrait Lens to market.  The New-Photo Miniature magazine wrote the following: "Equal Diffusion Portrait Lens, F4 (Gundlach-Manhattan Optical Co.)....As the name indicates, it is designed to meet the requirements of the portrait photographer; its largest aperture making it available for short exposures even under difficult light conditions. In form the lens is of the convertible type, consisting of two cemented combinations of unequal focal length. This gives the user a choice of three different focal lengths and makes the lens of great general utility. The chemical and visual foci of the combined lens and of each combination exactly coincide, which means that the image secured in the negative is identical with that obtained on the focusing screen, without further adjustment of the focus before exposure. The whole lens is corrected for a flat field at F:4, and gives an image free from flare or double lines under normal lighting conditions. The optical effect obtained in use is a soft but agreeably well-defined image with the brilliancy resulting from good chromatic correction. I am informed that the lens has been thoroughly tested in practice by several professionals of reputation with complete success, thus satisfying its makers that it fulfils all their claims for it."



As described above, the lens was a triple convertible.  The lens had 4 elements, 2 groups of 2 elements.  Therefore, the lens could be used as a whole, with just the front group, or just the rear group.  See the catalog page below for all the combinations of focal lengths and apertures applicable to each size.  By 1922, the lens name was changed to the Hyperion Diffusion Portrait Lens.