Autofocus

[brian257]

To set up autofocus is a switch on the end of the head how everyone is sensing distance? Seems that would work great for flat objects, but I have some switches to engrave that are contured and it sure would be nice if I had a sensor that kept the head in continual focus as it moved. Am I asking too much or is anyone doing this?

Also, when figuring the distance on the lens that is the focal point is it measured from the top or bottom surface of the lens or right in the middle of it? I realize that is is small variation, but if I am going to focus might as well focus dead on instead of a bit off.

[NickWL]

Wikipedia: For a thin lens in air, the focal length is the distance from the center of the lens to the principal foci (or focal points) of the lens.
Good enough for me!