I read that andythemechanic used this lens to collimate his blue diode:
Thorlabs C610TM-A FL = 4.0mm 0.60NA Geltech Mounted Asferische Lens
To get the best beam you could variate with the FL or with the NA.
I wondered what would be the best collimating lens to get the tightest beam with the lowest divergence.
Option 1: Lens with the lowest FL and highest NA
Option 2: Lens with highest FL and highest NA
Option 3: Lens with lowest FL and lowest NA
Option 4 Lens with highest FL and lowest NA
Mccarrot and andy both suggested option 2 but i think option 1. What do you think?