The role of optics in digital photography is in certain aspects quite different from that in conventional (silver-halide)
photography. We first give an overview on the different classes of the digital still camera market. In order to judge the
role of optics, one has to look on the different members of the transmission chain and their influence on image quality.
These are mainly:
(1) the optoelectronic image sensor with his modulation transfer function (MTF) and
the particular situation of sensor cross-talk (aliasing), which will be interpreted as
spatial frequency depending additive noise. A quantitative measure for this will be
(2) the optical low pass filter with his own MTF which is intended to minimize the
(3) the optical system which has to be in a well balanced equilibrium concerning
image quality with these components.
Besides MTF-considerations the generation of colour has significant influence on image quality. Here the appearance of
colour fringes is most disturbing and is due to different reasons.
First of all the widely used (RGB) Bayer mosaic filter gives rise to colour aliasing because of the enlarged pixel pitch in
the RGB-channels. Secondly the missing colour pixels in each channel must be interpolated from the corresponding
neighbours who also introduce colour artefacts. Last but not least the optical system may contribute to colour fringes if
the lateral chromatic aberrations are not corrected to a high degree.
Measurement equipment is presented for the quick measurement of modulation transfer function (MTF), image field curvature (FC), and chromatic aberration (CA) of optical systems. The measurement device is based on a cooled CCD-matrix element as image analyzer and on a set of pinholes as objects. It is intended to be used in final quality control of optical systems and is thus incorporated into a system of computer aided quality assurance (CAQ) which has been developed in the last few years. After a description of the hardware modules and the interface constellation to the computer hardware (for the various control and regulation systems), the structure of the associated software and the function within the CAQ-System is described. An example of the test procedure for a fixed focal length optical system is given.