| Most cameras have gain control, which tries to even out the signal over the full image. Hot spots will drive the camera to reduce the signal level, possibly erasing desired data. Conversely, a large amount of dark area will drive the camera to boost the signal and overdrive certain areas. The ability to illuminate an object so as to clearly see what is desired, and only that, is still more of an art than a science. Video imaging is further complicated by the camera's ability to see lower light levels and longer wavelengths than the human eye.
Transmitted Illumination
Transmitted Illumination is generally used with transparent or translucent objects. Sometimes used to cast a shadow simulating comparators. Entering angle and stray light can be significant.
Incident (Coaxial) Illumination
Incident (Coaxial) Illumination is most practical when used with highly reflective or specular objects, such as wafers of other polished specimens. Coaxial is very efficient mode of illumination. It provides light on opaque surfaces at high magnification. However, it is difficult to fill a large field-of-view with coaxial illuminators. There are two methods of producing incident (coaxial) illumination in your Optical Systems. - By injecting a beam above the taking lens with a beam splitter. In this method, the lens becomes the condenser and the light is highly controllable. The draw back is that some light will always reflect back off the lens surfaces and reduce contrast. The coaxial illuminators shown on the systems diagrams are of this design and provide excellent illumination when used within the confines indicated by the accompanying chart. Due to the angles of incidence, this type of illuminator cannot provide even illumination on large fields. It is restricted to higher power auxiliary lenses and higher recommended limits on the zoom setting dependent upon your camera format and TV Tube.
- The second method is to inject light below the lens. Qioptiq Imaging Solutions's new LF Coaxial Illuminator accessory is designed to attach to any existing Thales Optem Zoom system.
When staying with FMOS parts illumination options are somewhat limited. But with an adapter you can use Zoom 70XL as well as Zoom 125 illumination options on your FMOS system. Please contact us with any questions. |
