Parfocalling Microscope Objectives

Particular compound microscope objectives have a focusing ring that can be found when unscrewing the objective cover. Parfocalling microscope objectives is a procedure by which each objective is adjusted to remain in relative focus with the other. If each objective is not parfocalled, an object would not remain in clear focus when switching powers.

Not only is this inconvenient, it can increase eye strain and some wear and tear on your microscope. You may find parfocalling objectives too hard for you to perform yourself. Fortunately, most Meiji dealers have service persons on staff who can perform this task for you. But if you are mechanically inclined, the following procedure can be used as a general guide. Consequently, Meiji Techno assumes no liability in regards to the outcome of end users who disassemble objectives to perform this or other tasks. So be careful !

Remove the objectives to be parfocalled.

Each objective to be parfocalled will be removed and the outer covers opened.

If you have a 4X or 10X objective in your nosepiece, leave them screwed in. They do not have user adjustable settings.

The higher power objectives will be parfocalled starting with the objectives higher than 10X. The 10X will essentially be the starting point to which the other objectives will be adjusted.

Remove the outer objective cover.

The covers unscrews counter-clockwise like most threaded devices and should unthread pretty easily.

Keep track which covers go with which objectives !

This ring is the objective parfocal adjustment.

See if you can turn the ring.

The ring may or may not have a dab or drop of optical cement holding it in place.

You may have to look very carefully to find the cemented spot.

Remove the optical cement securing the adjustment ring.

Using acetone and a lightly dampened Q-tip, carefully remove the dab of cement holding the ring in place. You may have to work the ring back and forth to make the ring spin freely and to remove the debris in the threads.

After each ring is free, re-install the objectives ( without the covers on) on the microscope in their proper order of magnitude.

Rotate the 10X objective into working position and focus on your standard. We used a stage micrometer but you can use anything flat that has fine lines on it. Now switch to the next objective.

Apply optical cement to secure the objective adjustment.

When your objectives are all adjusted, you may want to secure them so they do not fall out of adjustment due to vibration or regular usage.

If you do not have optical cement, a small dot of clear nail polish can do the trick.

You can add the cement while the objectives are still screwed into the nosepiece. This photo shows where the cement is applied. Allow the cement to dry and re-install the objective covers.


The microscope objectives are now "parfocalled" and they should hold their focus each time you change powers. The exception would be the 4X objective. The 4X objective is your "scanner"; it's used to locate the general area of interest and not much else. The 40X and 100X should be parfocal with the 10X objective. Since the 10X objective does not have an adjustment ring, all other objectives that are adjustable use the 10X as a starting point. Your particular microscope may have a different number of objectives with different powers. However, the procedure will still remain the same.