La phase de réglage est assez longue et fastidieuse. En attendant une traduction, voici les liens vers les explications en anglais sur le site de lasersaur:
Page de réglage peu détaillée mais avec schémas: [[https://github.com/nortd/lasersaur/wiki/optics_setup]]

Page plus détaillée du processus: [[https://github.com/nortd/lasersaur/wiki/Calibrating-mirrors-and-lenses]]

Un montage pour aider au réglage des mirroirs avec un pointeur laser (pas testé): [[http://www.thingiverse.com/thing:639069]]

Une explication d'une méthode de réglage:
I'm a firm believer in NOT measuring the distance and assuming that's the
right thing to do.  You've gotta adjust incrementally.

One particular problem is that not all "75mm" lenses are really 75mm.
Some of them are 3 inches - which is 76.2mm - but they aren't necessarily
even that.  We're not keen on spending $300 for a lens from a 'reputable
vendor' - when we can get them for $60 from some guy in Israel who sells
them on eBay!  The cheaper lenses seem to have focusing ranges anywhere
from maybe 72mm to 78mm depending on where they originally came from.

I have the older focussing tubes where you rotate the lens tube to adjust
the focus.  The Thor Labs parts have 40 turns per inch threads.  I put a
white dot on the edge of the lens tube and count the number of rotations
up or down to get the thing in perfect focus.

So I measure off the 75mm "nominal" distance - and then cut a series of
10cm lines with the lens tube rotated in 2 turn increments (which is about
1.3mm) starting at 8 turns above the nominal distance and ending 8 turns
below it.  This is kinda tedious...but we only have to do it when we swap
out a lens.  We pick the best focussed line - and then try one turn above
and one turn below that setting to get the very best.

The final step is to rotate up in 1/4 turn increments...that's because
lenses get gradually damaged - and very often, by rotating the damaged
part somewhat out of the way of the beam (which is somewhat elliptical
after all of those mirror bounces) - you can sometimes get better results.

Also, focussing a millimeter or so higher than optimum gives the best
compromise when our plywood is a little warped and won't lay perfectly
flat on the bed.

We just bought one of the newer lens tubes that Nordt sell where the
entire tube slides up and down and you can't rotate it to get precision
adjustments - I was rather disappointed with it - and we're currently
debating whether to return it or to persevere with it.

I suppose we could get similar repeatability & accuracy with a wedge slid
under the tube, marked with it's thickness at various points...which is a
tool that we could laser cut.  But I'm not convinced because the retaining
ring below the lens can easily get turned around when you remove the upper
retaining ring to get the lens out for cleaning...that would mess up the
focus.  Since our lenses need cleaning every one or two days, that's an
extra chore that we really don't need.