the first manufacturer to show an early prototype 35 mm behind-the-lens metering SLR camera, which was named the Pentax Spotmatic. The camera was shown at the 1960 photokina show. The first TTL light metering SLR was the 1963 Topcon RE Super, which had the CdS metering cell placed behind the reflex mirror. Off the film metering In the 1970s Olympus marketed the OM-2 camera, which measured the exposure directly off the film (OTF). In OTF metering used by Olympus, metering was performed in one of two ways — or a combination of both — depending upon the shutter speed in use. In the OM-2's Auto Dynamic Metering (ADM) system the first shutter curtain had the lens-facing side coated with a computer generated pattern of white blocks to emulate an average scene. As the mirror flipped-up the metering cell in the base of the mirror box measured the light reflected from the subject bouncing off this pattern of blocks. The timing of the release of the second curtain was adjusted in real time during the actual exposure. As the shutter speed increased, the actual light reflecting off the film surface was measured and the timing of the second curtain's release adjusted accordingly. This gave cameras equipped with this system the ability to adjust to changes in lighting during the actual exposure which was useful for specialist applications such as photomicrography and astronomical photography. Leica later used a variation of this system, as did Pentax with their Integrated Direct Metering (IDM) in the LX camera. A variation of this "OTF" system was used on early Olympus E-Series digital cameras to fine-tune the exposure just before the first curtain was released; for this to work, the first curtain was coated in a neutral grey colour. Through the lens flash metering The process of calculating the correct amount of flash light can also be done 'through the lens'. This is being done in a significantly different way than non-flash 'through the lens' metering. The actual metering itself happens in two different ways, depending on the medium. Digital TTL works differently than analog TTL. The analog version of TTL works as follows: when the incoming light hits the film, a part of it is reflected towards a sensor. This sensor controls the flash. If enough light is captured, the flash is stopped. During early testing of this system by Minolta and Olympus it was found