Of course, the above rules can be conveniently combined to:
d = λ · F
And I suppose F/2 could also work if you are seriously lazy.
My LF357 (compensation caps are much smaller than on Noopy's so I figure it must be the 7) really looks quite fine despite the temperature. But I still haven't checked if it works because I try to keep it dust free for testing of my new microscopic system.
Project objectives:
- capability to inspect ICs still partly in the package (CERDIP, TO220 - these are very hard to remove completely)
- better structural rigidity than offered by a matchbox
- better image quality if possible, please
Long story short, I bought a lot of M42 macro extension tubes and some thread adapters. Then with that stuff and some plastic sheets and paperboard I constructed an M42 epi-illuminator (45° half-mirror plus a hole in the wall) and - possibly the first in the world - M42 mount webcam
I experimented with various setups and this is the winner so far: 10x biological microscope objective (abused at infinity focus, seems not to mind it much), the illuminator, Raynox DCR-250 macro, 125mm of M42 tube, the webcam. The whole tower is supported vertically above the IC by another stack of M42 tubes, partly unscrewed so they work as focus adjustment.
Remaining problems:
- some chromatic aberration - likely from the objective (it's old junk and I have dropped it on a hard surface once, so maybe that's why)
- still imperfect illumination, you can see some areas are brighter and/or different shade than others
Not problems:
- detail and resolution - nice and clean
- contrast and color - it's just this damn LF357 looking dull, I may upload some sexier dice later to show what the system is capable of
The LF357 picture below is a mosaic of 7×5 images captured with the webcam, stitched in hugin, postprocessed and scaled 50%. IMHO it's not too bad, and the setup is pretty low cost (the Raynox being the worst offender), mostly DIY and highly tweakable.