The full frame update rate of the guider camera needs to be fast enough not to annoy the observer. The subraster frame rate of the guider camera must be fast enough to track tip--tilt of the atmosphere, telescope shake and dome-induced seeing.

The resolution and field-of-view are set by the size of the detector, and the re-imaging optics in front of the guide camera. The trade-off is that the resolution must be fine enough to provide precise centroids, while the field-of-view (FOV) must be large enough to make it straightforward to acquire suitable guide stars.

Essentially, the requirements dictate the use of a back-illuminated, frame-transfer, low-noise CCD with an image area of 512 × 512 pixels. For a pixel size of 26 µm (or 13 µm binned 2×2), the re-imaged beam would be f/4.