So I took a moment to play with my new usb microscope and thought I would post a few notes on it.

First off this claimed to be a HD camera but really it only has 640x480 resolution.  With that said, this is enough to get the job done.  And chances are all the other low cost units on amazon and ebay have similar resolutions.  This one came with two holders, neither are worth anything.  You can easily hold the module by hand while adjusting focus, a holder is not needed.

I tried using my yellow filter to block most of the blue laser light.  I was hoping this would allow us to see the spot in more detail rather than just being blown out in the camera.  However it was a dud, it had no benefit on the light.  That is ok, I really picked up a variety pack of acrylic sheets.  I have always heard that blue lasers can't do anything with these, but I wanted to prove it for myself in a future experiment.

I had also picked up a pack of anodized aluminum black sample sheets to use as focus targets.  They work great, there is a lot less back scatter and the surface is smooth so it is easy to focus on consistently.  The spot is difficult to see with your eye (when wearing safety glasses) so you don't want to use these without a microscope.  You could do just as well by painting a smooth piece of plastic or metal matt black.  I really picked these up to experiment with lasering off the anodizing so I'm glad I got them.

The microscope works great, you can get the focus dialed in to within a mm or two, however it is difficult to get it dialed in perfect even with this.  There is just too much variability, even the pressure of your hand on the focus material is enough to add a mm of error.  You could probably improve accuracy by jogging the laser a bit out of focus on either side then splitting the difference, using some sort of reference to make sure the out of focus spot is the same size on either side.

I thought I had my laser set to focus 6 mm below the bottom of the laser housing, however it appears I had it set lower than I thought at 3-4 mm.  That may have colored some of my previous experiments.  It is very possible that the ramp test and this focus test give quite different results.  I will look into that next.  Anyway I found an aluminum block to use as a new focus block, I have not measured it yet but it appears to be about 15 mm tall.  I will try to find time to run a ramp test tomorrow and see how that compares to my manual focus.