after the rectilinear areas have been inclined the areas are moved in the direction away from the boundary of the vertical range e along the lengthwise direction of the areas along the arrow mark in of fig5 h in this case if the focus detection area marks which are displayed in the finder are the same as in fig5 e the area marks overlap with the end of the rectilinear areas as illustrated thus focus alignment determination is conducted with the image of the part corresponding to the area mark display of one end of the photoelectric conversion element array referring now to fig 6 this figure shows an isometric diagram of a focus detection system for an optical system in accordance with a second embodiment of the present invention the basic configuration of the optical system of fig6 is similar to the optical system of fig1 a 1 c in the case of fig1 the image reformation lens pairs and the photoelectric conversion element array pairs relating to the three cross shaped areas are integrally formed yet in the first embodiment there is little freedom for adjustment thus in order to introduce freedom for adjustment the image reformation lens parts 820 821 822 relating to each focus detection area and the photoelectric conversion element array parts corresponding to each lens are separate independently adjustable areas with regard to the cross shaped areas of both sides an identical photoelectric conversion element array can be used to.