Large Lens Opening: However, although a long focal length lens is mandatory, it need not be expensive. The utmost of critical sharpness in a portrait lens is not necessary, or even desired, since considerable diffusion can be tolerated in portrait negatives. Your lens needn't be in a shutter for strictly studio portraits, either. A lens in barrel is perfectly satisfactory, since you can provide yourself with a simple Packard shutter to use behind the lens. Many portrait men actually prefer the Packard to the more costly between-the-lens shutters.
De Meyer, who had begun exhibiting in 1894, was now producing portraits and large lens opening-scale still life arrangements taken with a soft-focus lens. This type of lens gave the pictorial photographer an optical control that could not be gained simply by throwing the image out of focus. With a true soft-focus lens, no part of the image is ever sharp because in their manufacture no correction is made for spherical aberration.
The first lens designed specifically for photographic purposes was Petzval's 1840 portrait lens. The images formed by this lens showed great loss of definition at the corners of the plate-a fault more theoretical than practical in portraiture, where edges mattered little. For outside work, however, particularly in photographing architecture, a lens with a flat field was desirable; and one free of spherical aberration, which caused straight lines to be imaged as slightly curved, was essential.
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Photography
