An experienced optical engineer can tell a great deal about a lens by just by looking at the image. A full discussion of this topic is beyond the scope of this manual, but here are some tips.

Use of a simple pinhole as the reticle is called a "star test". The comments below apply to such a test.

· Use PixelScope's powerful pan and zoom capability to zoom in on fine details in the image.

· It is OK to increase the illumination to bring out fine details in the "tail" of the intensity distribution. This will cause saturation in the brighter areas, but it will not damage the CCD.

· Observe the image as you move through the best focus. A perfect diffraction limited spot will broaden out symmetrically. (In other words, the spot will look the same on both sides of the best focus. ) Lack of symmetry about focus is a tip-off that spherical aberration may be present.

· Almost all lenses are at least intended to be axially symmetric. Lack of symmetry in the on-axis spot is a clue that fabrication errors may be present.

· Consider using the optional eyepiece to observe the image. The human eye has tremendous dynamic range, and you can often see detail that is difficult to capture with the CCD.