Tradition epifluorescence requires optical filter cubes to be positioned in a turret inside the microscope. However, filter-switching time is too long to allow for observation of many biological processes. The addition of an Optospin25 filter wheel allows excitation and emission filters to be changed rapidly (approximately 25 milliseconds).  This rapid changing of filters improves the time resolution of FRET and ratiometric imaging techniques.

The Cairn OptoSpin25 has been designed for compact and flexible operation. The OptoSpin25’s motor is mounted directly within the hub of the filter wheel, which both avoids the “motor bulge” present on other systems and minimizes the inertial losses associated with geared connections.  Equipped with a powerful new motor, the OptoSpin25 achieves low response times while still supporting 25 mm filters. The OptoSpin25 also offers a continuous spinning mode over a wide range of speeds. Continuous spinning allows wavelengths to be changed on a millisecond timescale, as required for high-speed imaging, and further reduces the vibration problems associated with stepwise operation.

For maximal functionality, the OptoSpin25 has been standardized on a six-filter wheel, but it is offset within its housing so that two housings can be joined in an interlocking fashion. This design allows both wheels to be incorporated within the same overall optical and mechanical path length of 35mm. This in turn allows the controller box to treat this combination as a single ten-position filter wheel (five active positions and one open position in each one), but with substantially reduced inertia – and hence stepping time – as compared to a single ten-position filter wheel.

The controller box can drive up to four filter wheels simultaneously and can interconnect with other equipment by either a digital or a USB interface. In spin mode, any or all wheels can be spun in both speed and phase synchronization. In step mode, wheels can be simultaneously but independently stepped between any combination of filter positions.