fig7 shows a typical example of a film pack according to the invention . in fig7 reference numeral 61 designates springs , or local depressing members . the ends of the springs 61 are connected to an abutment plate 62 . the springs 61 apply a biasing force or a force of depression to the film unit which is independent of the biasing force provided by the depressing plate 5 &# 39 ; ( indicated by the one - dot chain line ) of the conventional depressing unit . the term &# 34 ; independent &# 34 ; as used herein is intended to mean that the biasing force or the force of depression provided by the local depressing members to the film unit can be selected substantially irrespective of the biasing force or force of depression provided by the conventional depressing unit to the film unit . if the force of depression of the local depressing members or springs 61 applied to the film unit is excessively strong , as the photographing operation is repeated , i . e ., the number of film units in the film pack is reduced , peripheral portions of the top film unit are locally pushed so that the curvature of the top film units is reduced . in practice , the biasing force of the springs 61 should be determined according to the rigidity of the film unit , and the size and configuration of the abutment plate 62 coupled to the movable ends of the springs , although the abutment plate 62 can be omitted in some embodiments . according to the analysis made by the inventors , the curvature of the film unit 1 which is a photographing position ( the top film unit ) depends on the total number of film units remaining in the film pack . for instance , in the case of an &# 34 ; fi - 10 &# 34 ; film pack manufactured by fuji picture film co ., ( generally one film pack containing ten film units ), the amount and degree of curvature is greatest when relatively many film units remain in the film pack ). however , the top film unit can be maintained substantially flat even with the conventional depressing unit when the number of film units remaining in the film unit is relatively low , for example less than six in some cases . the reason the conventional depressing unit 5 operates satisfactorily when there are relatively few film units in the film pack is believed to be attributable to the fact that the pod 23 has a thickness greater than other sections of the film unit . accordingly , when film units are piled one on another , gaps are formed between the film units , especially at both end portions of each image forming region thereof , and therefore the biasing force of the depressing unit 5 is not sufficiently transmitted through the depressing plate 5 &# 39 ; to the top film unit 1 which is at the photographing position . accordingly , it is desirable that a strong biasing force be applied to peripheral portions of the film units by the springs 61 when the number of film units remaining in the film pack is large , and that the biasing force of the springs 61 be reduced abruptly as the number of film units in the film pack is decreased . it is also desirable that the biasing force of the springs 61 be minimal or zero when the number of film units remaining in the film pack is less than four , or less than five as the case may be . that is , the local depressing members should make no positive contribution to the flatness of the image forming region near the front end and / or the rear end of the film unit when there are relatively few film units in the film pack . accordingly , the local depressing members 61 are designed according to a load - displacement characteristic which is represented by the position of the spring when no load is applied and the elastic constant of the spring . simple and preferable concrete examples of the film pack constructed according to the present invention will now be described . in this concrete example , when the number of film units remaining in the film pack is small , the biasing force of the local depressing members is neglible compared to the biasing force exerted by the conventional depressing unit . when the local depressing force is applied to the film unit , its point of action exists only at the front end portion of the image forming region which is closer to the pod whereat substantial film unit curvature is liable to require correction . fig8 - a and 8 - b are a sectional view and a plan view , respectively , showing the conventional depressing unit 5 and local depressing members 71 in the film pack . the depressing unit has two spring legs 72 and 73 , with spring leg 72 fixed to the bottom of the film pack and the other spring leg 73 being slidable on the bottom ( reference numeral 7 in fig2 ) of the film pack and being extended to form an end portion 74 which is adapted to locally depress the film unit . in fig8 - a and 8 - b , the dimensions of the depressing unit and the local depressing members 71 , 74 are as follows : a = 16 mm , b = 11 mm , c = 10 mm , d = 146 mm , e = 60 mm , f = 35 mm , g = 25 mm , h = 99 mm , i = 11 mm and j = 9 mm . the plate thickness is 0 . 29 mm . the depressing members and the depressing unit are formed of an ordinary chemically processed steel . the elastic constant of one local depressing member 71 , 74 is about 180 g / mm . since four local depressing members 71 , 74 are employed in the example , the elastic constant of all the local depressing members 71 , 74 is about 720 g / mm . fig9 is a sectional view of the film unit in the concrete example . the dimensions are as follows : k = 150 mm , l = 22 mm , m = 12 mm and n = 0 . 5 mm . when ten film units are piled one on another under the force of depression , the sum of the thicknesses of the pods is 15 mm , the sum of the thicknesses of the traps is 12 mm , and the sum of the thicknesses of the image forming regions is 5 mm . other configurations and materials are similar to those of the film unit shown in fig3 and disclosed in japanese patent application laid - open no . 68828 / 1982 . fig1 - a shows the states of the conventional depressing unit ( indicated by the broken line ) and the local depressing members ( shaded in black ) in the film pack when ten film units are in the film pack ( similar to a film pack which is commercially available at present ), and fig1 - b shows the states of the conventional depressing unit and the local depressing members when three film units remain in the film pack . in fig1 - a , the end portion 74 of each local depressing member depresses the image forming region at about 5 cm from the boundary ( reference numeral 26 in fig3 - a ) of the image forming region according to its elastic constant . on the other hand , in fig1 - b , the end portion 74 is merely in contact with the film unit , applying substantially no force of depression to the film unit . table 1 below shows how the flatness of the photosensitive surface ( which is the exposure surface of the cover sheet 32 in fig3 - b ) of the top film unit at the photographing position is improved with the film pack constructed according to the present invention . table 1______________________________________the number offilm unitsremaining 10 7 5 3 1______________________________________conventional 2573 1760 1624 1083 948film packconcrete 948 948 1083 948 812example 1concrete 1083 1083 948 1083 948example 2______________________________________ in table 1 , the numerical values are those which have been measured according to the moire method , each value being the difference in level in μm between two portions of the image forming region of the film unit at the photographing position , which are curved , respectively , most inwardly and outwardly . thus , the film pack having the novel local depressing members according to the invention is more effective when more than four film units remain in the film pack , and the effect becomes significant as the number of film units remaining in the film pack increases . concrete example 2 is similar to the above - described concrete example 1 except that , instead of the local depressing members having four points of action as shown in fig8 - b , local depressing members having two points of action as shown in fig1 are employed . in concrete example 2 also , the flatness of the image forming region is improved as indicated in table 1 , with a result which is substantially the same as that of concrete example 1 . as is apparent from the above description , according to the invention , by merely providing relatively simple local depressing members in the film pack in such a manner that the local depressing members act independent of the conventional depressing unit , the curvature of a film unit to be exposed can be reduced significantly especially when the number of film units remaining in the film pack is large . therefore , sharper pictures can be made which allows the film size to be increased and / or the depth of focus to be decreased . these facts are not only effective in designing cameras but are also advantageous for instant picture systems . while the invention has been described in detail and with reference to specific embodiments thereof , it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof .