Circuit for the control of exposure time in photographic enlarging equipment

In a system for the control of exposure time in photographic enlarging equipment having a variable enlargement ratio, the improvement comprising:

• means, including light sensitive transducing means, for the generation of a first electric signal indicating light quantity, said light sensitive transducing means positioned a fixed distance to a negative plane of the enlarging equipment;
• a signal generator responsive to an enlargement ratio for generating a second electrical signal which is a function of said enlargement ratio;
• means responsive to said first and second signals for determining exposure time;
• and said means for generating an electrical signal indicating light quantity being transmitted through a switch which alternately couples said light sensitive electric transducer to said means responsive to said first and second signals at a controllable switching rate which follows an increasing or decreasing function with time.

In a system for the control of exposure time in photographic enlarging equipment having a variable enlargement ratio, the improvement comprising:

• means, including light sensitive transducing means, for the generation of a first electrical signal indicating light quantity, said light sensitive transducing means positioned a fixed distance to a negative plane of the enlarging equipment;
• a signal generator responsive to an enlargement ratio for generating a signal proportional to said enlargement ratio;
• a function generator connected to said signal generator and responsive to said signal proportional to said enlargement ratio for providing a second electrical signal proportional to the square of said enlargement ratio;
• and means responsive to said first and second electrical signals for determining exposure time.