Haag-Streit 900 BQ Slit Lamp: Focus Tweak. Adjusting you focal distance for clarity/sharpest image.*

If your focus changes when you turn your mag, you might need to re-calibrate your 40 mag. This assumes your eyepiece is on zero and you have nearly 20/20 vision. If your focus is clear on 40 mag, then, it should be in focus on all the other mags. *This procedure would also work for a BP. The BP would adjust focus for 25 mag which is the highest mag. *Note: If you are unable to turn the focus length adjustment screw, if you look under the screw you will find an access hole that has filler putty covering the locking screw. Remove the putty to gain access to the locking screw that locks the adjustment screw. After you have corrected the focus length, re-tighten the locking screw under the adjustment screw.