What is a filter wheel?

A filter wheel is usually a round disc (the filter support) with recesses that provide stable housing for various filters. Filter wheels with fixed, integrated filters are also used. Filter wheels often contain between five and twelve filters, but the number of possible filters depends solely on the diameter of the filter and the size of the wheel. All conceivable filters can be used in a filter wheel: for example neutral density filters, coloured glass filters or interference filters.
Filter wheels are mostly used in suitable carriers that can be rotated manually or with a stepper motor so that another filter can be placed in the beam path. In professional fields, computer control and automation of the filter change are common.
The advantage of a filter wheel is that the required filters can be selected and placed in the filter wheel prior to measurement. The measuring device must no longer be opened during measurement to change the filter.