Page:Austin Freeman - The Mystery of 31 New Inn.djvu/245

 inquisitive eye over the instrument. "Very fine one, too; I am a bit of a photographer myself. What is that graduation on the side-bar?"

"Those are the scales," replied Thorndyke, "that shows the degree of magnification or reduction. The pointer is fixed to the easel and travels with it, of course, showing the exact size of the photograph. When the pointer is opposite 0 the photograph will be identical in size with the object photographed; when it points to, say, X6, the photograph will be six times as long as the object, or magnified thirty-six times superficially, whereas if the pointer is at ÷6, the photograph will be a sixth of the length of the object, or one thirty-sixth superficial."

"Why are there two scales?" Mr. Britton asked.

"There is a separate scale for each of the two lenses that we principally use. For great magnification or reduction a lens of comparatively short focus must be used, but, as a long-focus lens gives a more perfect image, we use one of very long focus—thirty-six inches—for copying the same size or for slight magnification or reduction."

"Are you going to magnify these cheques?" Mr. Britton asked.

"Not in the first place," replied Thorndyke. "For convenience and speed I am going to photograph them half-size, so that six cheques will go on one whole plate. Afterwards we can enlarge from the negatives as much as we like. But we should probably enlarge only the signatures in any case."