Response to Focus free lens

From Richard Knoppow on USENET: The single meniscus lenses used on box cameras effectively have several focal lengths so the image is really a combination of a relatively sharp image and a blurry image of objects within a rather large range of distances. The sharp part of the image will be brighter than the blurred part so the result is very large depth of field but a rather low sharpness overall. A well correct lens will always focus on one plane only. Usually it will "pop" into focus, the point of best focus being very easy to find. Lenses which seem hard to focus usually will be found to have excessive uncorrected spherical aberration and really do not have a definite point of best focus.

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