This invention relates to a photographic enlarger for use in bright light having a light-tightly enclosed space, a transparency holder and an enlarging objective means therein, which space includes the image plane of the enlarging objective.
In recent years photography as a hobby has become increasingly popular but photo-hobbyists are finding it increasingly difficult to find a room at home which they can use as a dark-room where they can develop and print their films. Thus, to overcome this problem, recently there have been introduced devices which enable the whole processing and printing process to be carried out in normal daylight conditions, that is to say in unblacked-out rooms using normal lighting conditions. One piece of apparatus required is a daylight enlarger. Such enlargers often consist of an enlarger frame or casing draped with light-opaque materal, there being present a viewing window and a reflecting screen. When such an enlarger is used in daylight conditions it has been found difficult to focus a sharp image on the reflecting screen.
Most of the known enlargers for use in bright light, i.e., without requiring a dark room, do not incorporate special means with which to view the image in the device. However in the German Offenlegungsschrift No. 2,847,187 and in U.S. Pat. No. 3,890,043 enclosed frame enlargers are described in which a mirror movable into and out of the light projected through the transparency focuses an image of the transparency on a ground glass screen which is viewable by the operator from outside the enlarger. Such enlargers are of a rather complicated structure.
In French Pat. No. 2,455,756 there is described an overhead projector in which a transparency is focussed on a fresnel lens and then reflected upward to a condenser lens and to an inclined mirror which projects the image on to a screen. This is not an enlarger and certainly not an enclosed frame enlarger. Moreover a fresnel lens will only function in association with optical means required to derive a viewable image which are very expensive and complex.