Thanks ! Your links and explanations are the starting point I needed. Cool, this stuff's not rocket science after all !
The "infinity-focus " " Raspberry Pi camera:
good vision, but stuck at infinity." OK, I assume the lens the camera has merely focuses the parallel (from-infinity) rays onto the surface of the sensor. If so, for my near-field application, would removing and replacing the stock lens with my own be more practical, as the object will always be at a fixed distance ? ( Removal / replacement is no hurdle. )
rkinch: Focus the microscope eyepiece view at infinity, as is the proper technique.
Is focusing at infinity effectively taking the microscope (a source
device) out of the optical path - it appears
to the camera (or next optical gadget) as if the source weren't there ? ( Ignoring optical loss, of course. )
jbeale: strong lens ... depth of field is reduced. You mentioned "4 cm +/- 1 cm" but I don't know if you will have that much depth of field, without moving the lens.
I guess it'd be clearer to say 3 to 4 cm with a depth of field of 1 cm.
" Nice - a triplet lens listed at $68 for only $15 ! Do you all think it would do the job ? I could also go with 4 - 8 cm, if that were needed to get the 1 cm depth, but prefer to keep it shorter, and not have to move the lens, as this is intended as a remote, telemetric gadget.
Thanks again for the assistance - very much appreciated !