Rhodopsin vision in the dark. Several closely related opsins differ only in a few amino acids and in the wavelengths of light that they absorb most strongly. Humans have eight other opsins besides rhodopsin, as well as cryptochrome (light-sensitive, but not an opsin). The photopsins are found in the cone cells of the retina and are the basis of color vision. They have absorption maxima for yellowish-green (photopsin I), green (photopsin II), and bluish-violet (photopsin III) light. The remaining opsin, melanopsin, is found in photosensitive ganglion cells and absorbs blue light most strongly. In rhodopsin, the aldehyde group of retinal is
Kodak Retina Ausf. II Retina IIc, which is later mounted on the Type 019 Ausf. II Retina IB and Type 028 Retina IIIC. The second generation Type 034 Retina Reflex S of 1959 shared "S" type lenses with the Type 027 Retina IIIS (below), and offered fully coupled metering. With these the entire lens detached allowing for a wider range of focal lengths, 28mm to 200mm. At this point economical Japanese SLRs were becoming available and the Nikon F of 1959 would set the standard for future camera system. The Reflex III of 1961 and Reflex IV of 1964 brought minor improvements