A Focal Isolation Lens

The chromatic aberration of a single lens could be used to advantage sometimes as in a focal isolation device. If a single lens is used, the changing of the wavelength becomes a little inconvenient. A simple focal isolation device is described, wherein two plano-convex lenses which are aspherized are used. These lenses are made of fused silica to be useful in the 1900-2500-A region. The piano sides of these lenses are aspherized to correct for the spherical aberration. The entrance and exit holes are fixed in position and by moving the lenses by the same amount in opposite directions, the wavelength of maximum transmission could be changed. Some theoretical transmission curves are also presented at various wavelength settings.