cam plunger 48 is attached to handle 49 by means of a threaded fastener 51 handle 49 moves cam plunger 48 in a vertical direction against a spring pressure provided by spring 52 and spring plate 53 cam plunger 48 is controlled by handle 49 moving in a cam slot cut in a cam tube 54 which is held to motor mount 41 by means of a threaded fastener 55 lock bar 47 cooperates with a notch 56 cut in selector disc collar 26 thus by moving handle 49 a lock is provided to secure disc 25 against rotation by either motor 46 or speed selector ring 24 a variety of locking mechanism may be used to actually lock bar 47 and selection among them depends on trade offs which would be well within the skill of a person versed in the precision instrument and camera design arts referring to fig2 the details of the first shutter disc 21 are illustrated shutter disc 21 has a plurality of apertures spaced circumferentially about the surface thereof these apertures are in two diametrically opposed sets indicated with primed and unprimed numbers apertures 61 and 61 39 are the largest apertures and provide the longest exposure while apertures 65 and 65 39 are the narrowest apertures and provide the shortest exposure aperture 61 and 61 39 have an angular dimension of 21 u00b0 36 39 apertures 62 and 62 39 have an angular extent of 10 u00b0 48 39 apertures 63 have an angular extent of 4 u00b0 10 39 apertures 64 and 64 39 have an angular extent of 2 u00b0 10 39 while apertures 65 and 65 39 have an angular extent of 1 u00b0 52 39 thus in the illustrated embodiment each successive.