To found the better distance from the two corrective optics I applied the well-knowed method TRY AND ERROR.
First of all I firmly glue the first lens, then I begin to move backward/forward the other lens and observe the dot shape against a wall at least at a distance
of 10 meters.
When I found a decent (but not perfect) dot shape I mark with a felt tip pen the lens position, then I remove the lens and put under it a small drop of glue.
It is important to use a slow hardening glue, so I have all the time needed to found the correct lens position.
I put back the lens inside the lens holder at the markers and start again to move it back/forth, but with infinitesimal movements: every 1/10 of mm can change the dot shape a lot.
When I found the best dot shape obtainable I simply wait that the glue harden.
These lenses works well with blue and azure diode, but I think it works also with the Oclaro red diodes.
I think CDBEAM has tested this lenses with all the diodes :beer:
Thorland BE is pricey but has a "sliding lens" system, so when I rotate the focusing ring, the lens doesn't rotate, but it moves back/forth remaining in the same position. This is a much more precise system compared to the traditional "rotating system" lens. For example, if You have a laser with a not parallel-to-the-host output beam, when rotating the lens the dot also start to rotate and do not keep the same position. With "sliding lens" system this does not happen.
I mounted an extra converging lens to bring near the minimum focal point to the BE, but this is can be useful also if the input beam dimension exceed the maximum tolerance allowed by the BE lens input.
It is possible also to mount a second lens, so the input beam can be parallelized (the minimum focusing point will not change, but the input beam will be thinner).
I love the Thorlabs BE because it is modular, You can add everything you want, before and after