Condenser Lenses

The original version of the guide recommended using condenser lenses with built in diffusers. The idea was that the diffusers would prevent the LED emitter from being imaged onto the DMD leading to inhomogeneities in illumination. What we found was that the built in diffusers don’t work very well for the long beam paths associated with openSFDI. Too much light is lost around the edges which can lead to low light throughput and long exposure times.

We now recommend using aspheric condenser lenses without diffusers. Specifically the Thorlabs 16 mm focal length aspheric condensing lens ( ACL25416U-B ).

To align this lens first image the emitter on the DMD surface. You should see a series of stripes. Then move the lens toward or away from the LED until the image of the emitter is blurred and the illumination on the DMD is uniform. This should increase throughput and allow for shorter exposure times and faster imaging.