Abstract: A measuring instrument, such as a densitometer, that uses an incandescent lamp as a measuring light source is provided with a control stage for energizing the light source upon switch-on to prevent overshoot of the desired luminous flux from the lamp that occurs if the final energizing voltage is applied immediately. The control stage includes an amplifier with a negative feedback network that is fed with a reference voltage via a switch. The feedback network includes a resistance-capacitance element and is responsive to closure of the switch to establish the initial lamp energizing voltage at 1-2% below its final value and to allow the voltage to rise to its final value over a period of 1 to 3 seconds.

Abstract: Method and apparatus for determining the sharpness of a picture through evaluation of the absolute values of the density differences between adjacent points of the image in at least one selected area of the image. The absolute values are measured and compared with at least two threshold values. The absolute difference values obtained as a result of the comparison are then counted when they exceed the threshold values. The counts thus obtained are compared with reference count values to produce a decision output and when a plurality of decision outputs are obtained, these are combined to arrive at a decision as to the sharpness of the image.

Abstract: An apparatus for simultaneously viewing diapositives and front viewed pictures or images, especially transparent printed copies and prints produced therefrom under standardized illumination conditions, comprising a rear viewing device encompassing a support for supporting a diapositive or transparent positives or images and light source means arranged behind said support through which the light can be projected. There is also provided a front viewing device comprising a support for the front viewed image or picture and light source means arranged in front of said last-mentioned support. The rear viewing device and the front viewing device are hingedly interconnected with one another and can be selectively fixed in adjustable mutual angular positions relative to one another.