I have not got round to giving this a go yet, but have thought about combining the images and are my CS skills which are limited up to it. The prime thought being that as focus is moved so image size would alter. A bit of back up thinking and a net trawl brought me to Combine Z5 ( a freebe ) which I have now downloaded and printed the help file for.
Rainy days forecast so a bit of machining to make a camera mount for the milling table ( my focussing stage ) then I hope to give it a go.
Here is a link to Digital Outback Photo Review of Helicon Focus and CombineZ5 software. Seems to be one of those occasions when its good to be on PC.
http://www.outbackphoto.com/workflow/wf_72/essay.html
Don