Through the microscope

Scenario: You’re  trying to set up Kohler illumination on an old Lomo biolam or  Meopta microscope which has no centring mechanism on the condenser. You have the lamp centred and the field diaphragm pretty well centred and you’re ready to get the condenser centred. You pop your phase telescope in the eye tube, you look through it and horror of horrors you see something like this!

iris aperture squiffy


Your iris aperture (condenser aperture) is way off centre. When you enlarge the aperture part of it disappears out of view. Kohler is impossible. You’ve wiggled everything that can be wiggled and you’re about to start smacking things with a hammer in frustration. STOP! There is a solution and no microscopes have to be hit with anything.

Step 1) Remove the condenser and the stage – this shouldn’t be a problem, they come off fairly easily, especially if you remove the mirror so you can get a screw driver in more easily.


Removing Lomo stage

Removing Lomo stage

Step 2) Observe the condenser carrier. You will see a knurled locking screw and three tiny grub screws  – one at the front and two at the back on either side. These tiny grub screws are your centring mechanism but don’t bother trying to alter them yet, nothing will happen until you have taken off the locking ring.

Locking ring

Locking ring


Step 3)  Unscrew the locking ring -I used pointy ended pliers to get it started. Now you can  adjust the grub screws. Pop the condenser back while you do the adjustment. Rack the condenser almost completely up and look through the phase telescope using a low power objective. Make sure the objective is down near where the stage should be. It’s no good leaving it 20 cms up in the air.  It doesn’t matter that you have no stage and no slide to view, you’re only looking at the condenser aperture through a phase telescope.

Approximate position of grub screws shown by pink arrows

Locking ring removed. Approximate position of grub screws shown by pink arrows.


Step 4)  Adjust the grub screws until you see something resembling this through the phase telescope.

iris aperture central


Step 5)  Cry “Hallelujah!” then throw the locking ring in the bin. Well, put it somewhere safe, I have found everything to be perfectly secure without it and it’s much easier to adjust without it there.

Step 6) Put the stage back on. Good luck with that, it’s fiddly. Put the mirror back on, put on anything else you removed.

Now you can set up Kohler in the usual way.

NB. you may have to adjust the head  if that is out of whack rather than the condenser. The head has a dove tail slider which is obvious and easy to adjust. You have probably wiggled it several times during your attempts to get the condenser centred.




Comments on: "Centring a lomo or meopta condenser" (2)

  1. I’ve never tried Kohler illumination. I’m just recently retired, so lack of time should not be such an excuse 🙂 I really should give it a try.


  2. Yes, you must try. My friend set me a task to help me get kohler right. Look at the diatom Pleurosigma angulatum with a 40X objective. If you can resolve the dots on that with a 40X objective you are doing well. Compare with some pictures by someone incredibly brilliant like Charles Krebs to check you are seeing the dots as black/white.


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