Generally we tend to use auto iris lenses externally where there are variations in the lighting levels. In contrast, manual iris lenses are normally for internal applications where the light level remains constant. With the introduction of electronic iris cameras it is now possible to use manual iris lenses in varying light conditions and the camera will electronically compensate, however there are several considerations to this option. The setting of the F stop becomes critical if the iris is opened fully to allow the camera to work at night. The depth of field will be very small and it may be more difficult to achieve sharp focus even during the day. The camera can maintain normal video levels but it cannot affect the depth of field. If the iris is closed to increase the depth of field in low light, performance of the camera will now be reduced.