Hello, I would like to reduce the beam size of a laser by a factor of 10, with the purpose of replacing a long (750 mm) lens with a more compact design. Ideally I'd make a Galilean lens pair where the ratio of the focal lengths are 10:1 to produce a small collimated beam. However, I think I could achieve my desired result (small beam just over some length) by using e.g. a 2:1 lens pair and moving the diverging lens "too close" to the converging lens, achieving a gentle focus and long confocal length. Questions: How would one calculate the Gaussian beam parameters (waist, Rayleigh length, etc.) given the combined focal length 1/f= 1/f1 + 1/f2 -d/(f1*f2)? Would I use it "straight" in those formulas? Thank you!