Originally Posted by
Ernest Purdum
Brian K.. In the usual use of an enlarging lens, you have a smaller negative behind the lens and a larger piece of paper in front. In photographing a small, but not macro size subject, you have the same relationship - small behind, large in front. You are, therefore, working near, quite posssibly right at, the ratio for which the lens was optimized.
Unless truly symmetrical, an enlarging lens used past the 1:1 ratio will probably work better if reversed.
Most process lenses are either dialytes (the type favored for the huge horizontal cameras), or plasmats (the type adopted for use of the vertical cameras that need wider coverage). These types are particularly insensitive to variations in subject/image ratio, so perform quite well at infinity when used at the apertures most commonly used in large format work anyway. The other way around, plasmats intended for general-purpose use, are usually near symmetrical, but with some variation intended to optimize the lens for distance work. This means that a lens optimized for enlarging type ratios may, but not necessarily will, perform better than a general use lens at tabletop distances.
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