  We describe a two-beam interference structured illumination fluorescence
microscope. The novelty of the presented system lies in its simplicity. A
programmable electro-optical spatial light modulator in an intermediate image
plane enables precise and rapid control of the excitation pattern in the
specimen. The contrast of the projected light pattern is strongly influenced by
the polarization state of the light entering the high NA objective. To achieve
high contrast, we use a segmented polarizer. Furthermore, a mask with six holes
blocks unwanted components in the spatial frequency spectrum of the
illumination grating. Both these passive components serve their purpose in a
simpler and almost as efficient way as active components. We demonstrate a
lateral resolution of 114.2 +- 9.5 nm at a frame rate of 7.6 fps per
reconstructed 2D slice.
