Phase Without a Phase Condenser

I have a number of phase contrast objectives for which I have no suitable phase contrast substage condenser.

This need not be a problem - all you need is a conventional condenser with a substage filter holder and a suitable patch or wheel stop.

You can prepare a range of patch stops by printing discs with different sized central black spots on overhead transparency film and cutting them out, or you can just cut transparent discs and stick different sized black spots in their centres.

These can be used for darkground or circular oblique illumination (COL).

A Range of Patch-Stops

These can also be used for phase contrast as follows:

Set up the substage condenser in the normal manner - central and correctly focused on a test object. Move the test object out of the field of view.

Take out the microscope eyepiece and with the field and condenser diaphragms wide open examine the back lens of the phase objective. You should see the phase annulus as a dark ring.

Place a patch stop in the substage filter holder and swing in - you need to choose one that fits neatly in the centre of the objective phase annulus:

Patch too small

 

Just Right!

Start closing down the condenser diaphragm until it just encloses the annulus::

Diaphragm closing

Diaphragm Just Enclosing Annulus

Put your eyepiece back in. You are now ready to use phase contrast (and you've saved some money on a condenser)!

 

 

 

 

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