I have question about your technique...you said:
"I start the brevis, get a focus daisy wheel test chart (one is attached to the back of my slate - you can download them from the net) and get the best possible focus on the chart, normally using a 50mm lens, filling the frame with the chart. Then I hit the auto focus button. (temporarily) This pops in the last little bit of focus, if I've moved the focus slightly in taping the focus ring, it fixes that..."
My question is: if you have the lens attached to the Brevis and the camera focus rings are taped, and then you press the autofocus button to resolve the last bit of focus,... isn't that useless since that focus is only made for the currently mounted lens at that particular distance from your camera? If you decide to focus on an object at different distance from your camera with the same lens, wouldn't it be off? AND if you decided to change lenses, wouldn't that be off too? Thanks for your reply in advance.