Lenses are the second part in the chain of image processing. Optimized illumination of an object provides the best conditions to transfer the image information from the object to the camera. This transfer is accomplished with optics, which may be a specially designed and extremely complex package (see image) or a simple combination of basic lenses. A lens (or better an objective containing several lenses) is always designed for certain parameters. It is always a compromise between magnification, field of view (FOV), F-number, spectral range, image size, aberrations, and finally costs. The resolution determined by the camera's pixel size is often only reachable with very expensive lenses - inexpensive lenses have usually a resolution of two or three pixels. A general limit on an objective's resolution is given by diffraction, which is roughly equal to the F-number expressed in microns. The right choice of lenses is just as important as the choice of illumination. For some tips on choosing lenses, please see the "Optics Recommendation Guide".
