Microscope eyepieces adjustment explained

How to adjust your microscope eyepiece

If your lab or classroom uses shared microscopes, the first thing you should do before getting down to work is adjust your eyepieces.

Everyone’s eyes are different – the distance between your eyes will be different from other people's and your left eye often sees a little differently from your right eye.

Fortunately, microscope manufacturers are aware of this, and most microscopes let you easily compensate for the differences. 

Follow these simple steps. 

  1. Adjust for the distance between your eyes

The first thing to do is to adjust for how far apart your eyes are (sometimes known as the interpupillary or interocular distance).

It’s very easy to do – simply try to look down the eyepiece with both eyes. The goal is to be able to see a single image. If you can see 2 images, you need to move the eyepieces closer or further apart until they merge into a single image.

That’s all it takes.

If you can remember the distance (you can usually see it on a scale on the central area between the eyepieces), you can be ready to go on any microscope in seconds.

It’s worth remembering that eyepiece distances are often adjusted by moving them in a vertical motion (a bit like how a bird flaps its wings), rather than horizontally, so make sure not to accidentally pull your eyepieces apart.

  1. Account for any difference between your eyes

Adjusting the microscope to compensate for any difference between your left and right eye is slightly more involved. 

It’s very common for each of your eyes to be a little different. If you have glasses, you’re probably aware of this – your prescription compensates for the difference in the ‘strength’ of your vision in each eye.

For most people, the difference is usually very slight and may be unnoticeable in everyday life, but when using a microscope for lengthy periods you can sometimes end up with headaches and dizziness.

To compensate for any difference, you need to manually adjust your eyepieces.

Some microscopes have a single adjustable eyepiece with the other fixed in place, while others let you adjust both. The process is virtually identical either way, so don’t worry.

  1. The first step is to turn the eyepiece(s) until the number ‘0’ on the eyepiece(s) is aligned with the white line on the edge of the immobile part of the eyepiece.

(If you wear your prescription glasses while you work, you shouldn’t need to do any further steps because your vision is already corrected)

  1. Put a sample slide under your microscope and switch to the 10x objective lens.
  1. Look down one of the microscope eyepieces while keeping the other eye closed. If one eyepiece isn’t adjustable, look down that one first.
  1. Using the coarse and fine control knobs, bring the image into focus for that one eye.
  1. Once it’s in focus, shut the eye you’ve been using and look down the other eyepiece with your other eye.
  1. Instead of using the control knobs, adjust the eyepiece you’re looking down by rotating it until the image comes into focus.
  1. Both of your eyes should now be ready to go, but it’s a good idea to switch up to the 40x lens and make sure that both eyes are still in focus – visual differences can be more pronounced at higher magnifications, and you may have to repeat the procedure.

Next, note the number settings written around the side of the eyepieces. Once they are memorised, you can be ready to go with a simple adjustment the next time you sit down at a microscope.


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