Day time single source focusing mode

[fergusL]

Huntsman autofocus is less robust during the day as there are less detectable sources in any given FoV that can be used for focusing. Currently the autofocus examines a fixed region/window of the image to determine focus metrics. Consequently, this autofocus window must be relatively large to ensure that it will contain a source(s) to focus on. During the day this often results in a window with a single source and a lot of background.
A simple improvement for day time focusing is to add a single source focus mode, where initially images are taken with different focus settings until a signal peak exceeding some threshold is found. The location of this peak can then be used as the centre for a much smaller day time autofocus window, which should allow for more robust day time focusing.