One of the design tradeoffs is how many channels to have in the vertical and horizontal directions in the array.  The larger the number of channels the more uniform the illumination at the illumination plane.  However the edges between the lenslets are not infinitely sharp, and so light gets scattered by these edges out of the beam. The more lenslets, the worse this scattering becomes.

Odd or even number of channels is another choice.  An odd number of channels mean that the center channel is always on center and the channels to either side of the center channel are optically folded onto the center channel and this is where the spatial homogenization comes from.  Even numbers of lenslets can lead to a dip in intensity at the center.

As a generalization, approximately 7 channels is the minimum number required to achieve a uniform irradiance at the illumination plane of a digital projector and about 11 is the maximum.  Since these are general numbers make sure you model the illumination system from the source to the illumination plane to determine precisely how many channels are required in your fly’s eye arrays.

The focal length of the lenslets determines the spacing between the two arrays.  The aperture of each channel and the focal length of the objective array determines the field of view that the field array can transmit.  The channel aperture and focal length and spacing of the two arrays determine the size of the illumination plane in both directions horizontal and vertical.  One way to think of the field array is that the job of an individual lenslet is to image the aperture of that channel's objective array to the illumination plane with a certain magnification.

In LCD and LCoS digital projector light engines where the light source must be polarized prior to reaching the illumination plane a polarization conversion assembly or PCS is often used.  The PCS array is often cemented to the plano side of the field array to provide a common mounting and rigid support for the PCS array rhombs.