SOFT FOCUS LENSES & THE COOKE PS945
“Let there be light”
Light is a gift to photographers from the sun. Capturing the light on film and making it into a photograph is the gift of some clever scientists of the last two centuries.
The means of projection or concentration of light to form an image on the light sensitive material or sensor can be made with a pinhole lens, or much more efficiently, with a transparent glass lens. Lenses are sophisticated prisms with continuous curved surfaces. They focus light to form images. Various glasses of different refractive indices and densities, ground and joined together in compound lenses make images with different characteristics. Since the mid 19th C, photographers have depended on lenses that make clear images on films of decreasing size, with greater contrast and wider coverage, for easier use and convenience. The evolution of soft focus (abbreviated sf) lenses has paralleled sharp lenses. “Soft Focus” lenses are sometimes small meniscus, or landscape lenses, but are mostly large and heavy, made for portrait cameras. Many of the older portrait lenses are in 12" to 21" focal lengths, fit on 6" to 10" lens boards and weigh several pounds without a built in shutter. They were made to project images onto large sheets of film which were retouched by hand and then contact printed. In the last seventy years, there have been some smaller lenses made, in 6" to 10" focal lengths, and a few special lenses made for 35mm cameras, all with their limitations when used in modern cameras. They were made for black & white film and color corrected for red and green light, to achromatic standards, which usually means that there was a blue cast over the image which did not show in B&W film, but when color film or digital sensors are used as the recording medium, color fringing and color casts are unattractive image qualities which need to be removed if the image is to be of any use.
How to use sf lenses requires knowledge of the “look” they project, usually not very sharp when used at wide apertures. Commercial lenses, when used at wide apertures, project a sharp plane of focus. With all lenses, everything in front of, and behind the plane is noticeably out of focus. The way in which the out of focus areas appear is known by the Japanese word, "bokeh"
Soft Focus lenses all become sharper as they are closed down to smaller apertures. Most of them are actually quite sharp from about ƒ/11 on, as the aperture is closed further. Beyond about ƒ/16, the image deteriorates as the aberrations increase, but the image looks more “clear” because the depth of field increases. All lenses project aberrations, such as diffraction, as they are closed down - including sharp, expensive lenses.
The mystery and the magic of the soft focus lenses is in the quality of the focused image, and the “bokeh” when used between about ƒ/11 and full aperture (the iris diameter increases).
Soft Focus lenses can be simple meniscus lenses, like a spectacle lens, a doublet, like the achromat objective lens of a binocular, or two cemented doublets on each side of the aperture, known as a "combination" lens, like a rapid rectilinear, or a triplet like the Cooke lenses, or the Leitz (Leica)Thambar for 35mm.
Many sf lenses, like the Verito, look "fuzzy" as they are opened up to wide apertures. (Many lenses are fuzzy unintentionally when they are trying to be sharp, but this is not the category we think about as sf lenses.) Many inexpensive lenses are "soft" accidentally and not through any particular aim of optical design other than reducing the cost.
The more interesting lenses which feature a soft focus look, by design, are the Kodak Portrait lenses, the Nicola Persheid, and the more complicated Cooke Portrait lenses. The Cooke "knucklers" (two fingers are used to operate a "brass knuckle" handle which moves an inner element), and the Voigtländer Universal Heliars, allow variation of the degree of sharpness by the movement of a lens element in relation to the others in the lens. The softness can be controlled by movement of the movable element as well as the aperture diameter. This allows better control of the d.o.f. and the degree of softness, a useful extra creative tool for the photographer who understands how to use it.
The Rodenstock Imagon prejects a luminous image by using a disc with multiple holes around a primary hole which serves as the aperture. Fuji sf lenses use this technique in a slightly different way. The limiting side of this method is that the discs are fussy to use, get lost, fall off, and the apertures are very limiting. The most serious limitation for modern use with color sensors or film is that they are not color corrected.
The most interesting of the sf lenses for my taste are the Pinkham & Smith lenses, made in Cambridge, Massachusetts. They were made using hand ground aspheric lens elements which project a sharp image within a soft image. It is as if the lens projects two images at the same time, one sharp, one soft, and the combination is airy and luminous. This technique of using aspheric lens surfaces is different from most other sf lenses which use spherical aberrations to soften the image. The downside to the P&S lenses is that they are BIG and heavy, usually made for 8 x 10 cameras, some for 5 x 7 but very few, and they all require studio or packard shutters to be useful on a camera. They are also expensive and “collectible”. A P&S is not a lens easily used for snapshots at a picnic.
The new Cooke PS945 lens has given photographers a new edge. It has the magic image of the Pinkham & Smith lens (the PS in PS945 is a tribute to P&S), a 9" lens for 4x5 inch format, made to fit a modern shutter (Copal No 3) and fits on a 4" lens board and a Technika lens board. It also fits on a 4x5 Graflex Super D single lens reflex camera so the lens can be used with a hand held camera. The syncronized Copal 3 shutter has a reasonable set of shutter speeds to control exposure with film, or digital sensors.
The PS945 is also color corrected and has excellent, optically accurate multi coatings which help to project overall and micro contrast in the image. The lens can be used at full aperture, ƒ/4.5, to give a sharp image with a very soft surrounding luminous overlay - much faster than most sf lenses like the Imagon. It has the speed of the Verito with the complex image of the P&S in a useful shutter. As the aperture is closed down, the soft and the sharp images come together and by about ƒ/11 the image is quite sharp and looks more like a sharp commercial lens. However it is never really like a sharp lens because even at the small apertures the image "bokeh" is not like a commercial lens. This lens gives a smooth misty look to the out of focus areas, something the connoisseurs of image quality really like. The Cooke PS 945 becomes a "universal" lens which is particularly well suited to making portraits and also useful, with aperture closed down, for luminous landscape images.
The Cooke PS945 is an excellent landscape lens because it is sharp enough at small apertures without making the plane of focus pop out from the rest of the image. The out of focus area is beautifully rendered, unlike that of many commercial sharp lenses. The soft and sharp parts of the image are more visually integrated.
The Cooke PS945 is a welcome development in lens design and manufacture - and it is unique.
©CLIVERUSS.com