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It was rotated, by means of a winch and rackwork.

These points will be gone into later, and also details as to various types of objectives and their respective advantages; but it may be said here that a lantern objective consists usually of a combination of lenses of 2 inches or 2� inches diameter mounted in a rackwork focussing system at a distance from the slide of 6 inches to 18 inches, according to the length of its 'focus.'

In taking portraits, if you are not an adept in obtaining a focus, cut a slip of newspaper about four inches long, and one and a half wide, and turn up one end so as it may be held between the lips, taking care that the rest be presented quite flat to the camera; with the help of a magnifying-glass set a correct focus to this, and afterwards draw in the tube carrying the lenses about one-sixteenth of a turn of the screw of the rackwork.