Powerful Lens: By the assistance of a powerful lens, which magnified fifty times, applied to the delineation, every letter was clearly and distinctly legible, and so also were the minutist breaks and lines in the walls of the buildings; and the pavements of the streets. The effect of the lens upon the picture was in a great degree like that of the telescope in nature.
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.
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
