Adjusting Parfocality

Most compound microscopes are already parfocal when purchased new. Sometimes you will still have to make slight adjustments with the fine focus when switching objectives; acceptable parfocality is typically within a half-turn of the fine focus knob, clockwise or counterclockwise. If you have to turn the knob much more than that just to get a clear image, try the steps below to adjust parfocality.*
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If you have a camera mounted to a trinocular tube or integrated into the head:

1. Focus on the specimen using the focusing knobs until you get a sharp image through the monitor / display.

2. Looking through the eyepieces, focus each one until you get a sharp image. You may follow the steps in the section "Adjusting the Diopters" in our focusing instructions.
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If you don't have a camera installed:

1. Switch to the highest magnification objective.

2. Using the coarse and fine focus knobs, focus the image until it is sharp.

3. Switch to the lowest magnification objective.

4. Without touching the focus knobs, focus the eyepieces until you get a clear image through each eye (see the section "Adjusting the Diopters" in our focusing instructions).
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The above steps are probably the easiest way to resolve issues with parfocality, but if you still have problems, you can try to adjust the objectives directly by removing the covers and optical cement if necessary, reinstalling them to find the proper adjustment, and re-cementing them. Before you do that, though, you may want to contact the manufacturer or distributor of your specific model to check whether this is advisable.

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* Rottenfusser, Rudi; Wilson, Erin E.; Davidson, Michael W. Practical Use of the Microscope.