|
Three-dimensional imaging in telecentric systems of non-unity magnification is considered using a scalar approximation. It is well-known that it is not possible for such an optical system to form a perfect image of a 3-D object. This follows from the fact that the sine and Herschel conditions, which must be satisfied to ensure perfect transverse and axial imaging respectively, cannot simultaneously hold. The shape of the point spread function (psf) of a high-aperture system depends on its aperture. We consider the question: is the image the convolution of the object with the psf in object space, or of the magnified object with the psf in image space? We show that the imaging performance can be very different according to whether the image is formed directly in the image space or by scanning in the object space. This result does not violate the principle of reciprocity. The point spread function has been investigated for systems obeying, amongst others, either the sine or Herschel conditions. A clarification of the principle of equivalence between conventional and scanning microscopes is given. Imaging in confocal microscopes is discussed, it being shown that, in disagreement with some previously published work, the behaviour is symmetrical with respect to the two (projection and collection) lenses.
|
