The Novoflex Screw MT Reflex Housing displays an image through the camera's lens and eliminates common parallax errors on a typical rangefinder system esp. at close range focusing where it started to increase as the focusing distance decreases. The angle of view of a given lens also changes with distance. Overall, rangefinder focusing can be very accurate for normal to moderate  wideangle  photography. But at extreme both ends of the spectrum in particularly macro, duplication & long telephotography, its weakness will become apparent. Rangefinder focusing system uses a built-in bright-line frame inside the finder to aid photographer with the lens' picture angle. However, the system has physical constraints esp. when using with  ultrawideangles  and telephotos where the bright-line frame becomes too small.