Filter Wheels
Filter wheels are used on microscopes, cameras, and video systems to position a selection of filters quickly and accurately over a lens or array of lenses. They are used in machine vision, part inspection and research applications, especially those involving fluorescent microscopy, spectrophotometry, photometry, color CCD photography, laboratory applications, and optical and infrared imaging. This area focuses on the wheels themselves. For replacement lenses, or varied configurations, it is best to check with the manufacturer.
Filter wheels are generally available in configurations with between three and twelve lenses or filters. Normally, the first lens is a simple clear filter. The other lenses in the wheel may be of different colors, lens thickness, lens materials, or any combination thereof. Custom and specialized filter wheels are available with more than twelve filters.
In addition to the number of filters, filter wheels may be configured in systems with more than one wheel. This allows for additional colors or views to be used, as well as, the possibility of overlapping filters to allow for widely varied views. A system with two six-filter wheels could provide twelve separate, individual views, with the potential for as many as thirty-six overlapping views. However, it is very rare that this many options would be available, as many lens types will not work together.
Filter wheels are available in manual, motorized via controller, and motorized via computer interface designs. Manual wheels are simply tuned by hand. They are generally used in situations where filter changes are infrequent.
Motorized via controller systems are designed with a packaged control unit for wheel indexing, typically with keypad, buttons, or other local interface.
When using motorized via computer interface driven systems, the wheel can communicate directly with the computer via communication such as RS232 or GPIB, and run set modes, or function within set parameters.
Neutral Density (ND) filters are available with some styles of filter wheels. ND filters attenuate the light passing through the subsequent optics. They can provide enhanced color balance and allow for aperture adjustment for depth-of-field effects. Sets of ND filters are often graduated in degrees of light absorption.
