How to centre a microscope darkfield condenser

How to centre a darkfield condenser 

Darkfield microscopy is a technique that uses oblique lighting and a dark background to illuminate hard-to-see samples.

If you’re going to get the best out of your darkfield condenser, you need to make sure it’s properly centred.

The centering process is simple, but there are some slight differences between dry and oil darkfield condensers.

Centering a dry darkfield condenser

1. Rotate your 10x objective lens into the viewing position. (This is the lens with the yellow ring around it)

2. Remove one of the eyepieces from your microscope. Looking down the eyepiece-less ocular port, you’ll be able to see an image of the condenser and the dark or opaque disk in the middle of it.

3. Adjust the height of the condenser and the stage until the dark disk almost covers the viewing area. (You want to be able to see a ring of light around the outside of the disk.)

4. Adjust the centering screws of your condenser until the dark disk is in the dead centre of the ring of light. (The silver centering screws are usually found sticking out of the sides of the condenser. You can move the disk by rotating the screws back and forth.)

Centering an oil darkfield condenser

1. Rotate your 40x objective lens into position. (This is the lens with the blue ring around it).

2. Remove one of the eyepieces from your microscope. Looking down the eyepiece-less ocular port, you’ll be able to see an image of the condenser.

3. Raise the condenser until you can clearly see a dark circle. The circle might appear a little fuzzy around the edges.

4. Adjust the centering screws on your condenser until the dark circle is in the dead centre of the viewing area. (As with the dry condenser, the silver centering screws are usually found sticking out of the sides of the condenser. You can move the dark circle by rotating the screws back and forth.)

Setup an oil dark field condenser with a centering telescope

If you have a centering telescope lens to hand it is easier to centre your darkfield condenser.

1. Remove one of the eyepieces and insert the centering telescope.
   
   
2. Using the 40x objective, looking down the telescoping lens raise the condenser until you can see a dark circle.
   
   
3. Rotate the telescope lens clockwise or anti clockwise until the circle is focused.
   
   
4. Adjust the centering screws on the condenser to centre it. 
   
   
5. When centered you can remove the lens and refit the eyepiece and you are good to go.
   
   
6. If using a 100x objective for ultra dark field microscopy you may need to readjust the condensers centering screws minimally to recenter the dark field circle.

That’s all it takes – your condenser is setup and ready to go!