A shutter is located inside the camera barrel for precise control of exposure time. The shutter uses two blades to insure constant exposure time across the detector. The shutter is air-powered. The shutter may be removed/installed without removing the camera barrel from the instrument. The minimum shutter exposure is 2 seconds (1 second goal) with 1% linearity over the duration of the exposure. The shutter aperture is approximately 200 mm diameter in both cameras.