What is the Siedentopf Head on a Microscope?

The Siedentopf head on a microscope enables you to easily adjust the distance between the eyepieces (called the interpupillary distance) without losing focus on the specimen.

Other types of binocular heads, like the sliding head, can slightly lose focus when you adjust the eyepieces to make them more comfortable.

Therefore, it’s widely held that the Siedentopf head is a superior type of binocular microscope head than competitors.

You’ll find the Siedentopf head on most intermediate level compound light microscopes available from top brands like Amscope and Swift today.

This is a Siedentopf head microscope. Notice how you can pinch the eyepieces together or farther apart like binoculars:

Here’s how it works.

> This article is from our series on the Parts of a Microscope

History of the Siedentopf Head

The Siedentopf Head was invented by Henry Siedentopf in the early 1900s ^[1]. Siedentopf was working for the very famous Carl Zeiss AG microscopy company at the time, which is responsible for many advances in microscopy (including the Abbe condenser).

The premise of this microscope head is that you can adjust what’s called the “interpupillary distance” (the distance between the eyepieces) without affecting overall focus of the microscope.

This is achieved by allowing the two eyepieces to rotate around a single axis rather than having them ‘slide’ closer and father apart.

Benefits

The Siedentopf head was primarily an advancement in comfort and user experience. It works very much like binoculars, where you ‘squeeze’ the two eyepieces together so they fit comfortably over your eyes.

You can make regular small adjustments while looking at your specimen without being concerned about losing the fine focus.

Downsides

While there aren’t, in my opinion, any significant downsides of the Siednetopf head, they’re still not the only thing you need to take into consideration when looking at which type of microscope head you’re choosing to buy.

For example, monocular compound light microscopes are popular for school labs and especially middle school students. One primary reason for this is they’re simple and require less fiddling. Students can look through just one eyepiece and don’t need to adjust it.

A monocular head is usually cheaper because you’re using half as much hardware.

Another consideration is whether you want a trinocular rather than a binocular head. A trinocular head also has a port coming out the top of the microscope for taking pictures.

But, trinocular microscopes and Siedentopf heads are not mutually exclusive. My Amscope T490B, for example, is a trinocular head microscope with a Siedentopf binocular section included.

How to use a Siedentopf Head Microscope

One thing you may notice with a Siedentopf microscope is it has markers on either side to indicate the distance between the center of the two eyepieces:

So, you can see four markings here: 75, 70, 60 and 50. If the distance between the center of your eyes is 70mm, you’ll want to set the eyepieces to the ’70’ marker. You can see that I have mine set at 60. On any microscope I use, I can always set it to 60 because I know my interpupillary distance.

I asked around on reddit for clarification of this, and I got some great answers and tips. u/HowHaveIEndedUpHere says:

It’s the distance between the middle of the eyepieces. It is the inter-pupillary distance. If you know your IPD, you just move the eyepieces to the correct distance.
Make a note of the number, and it should be the same on any decent microscope.
Also make a note of the difference between the diopters on the/each eyepiece.
Remembering these two numbers makes getting started on a new microscope, or one used by someone else much, much quicker.

(See the full reddit conversation about the Siedentopf head here).

When you adjust the interpupillary distance, try to keep the angle equal for each eyepiece so it remains perfectly horizontal. This will ensure optimal comfort when using the microscope.

What is Interpupillary Distance and what’s it got to do with a Siedentopf Microscope?

Interpupillary distance is the distance between the center of your eyes. Different people will have a different interpupillary distance. This simply depends on how close together your eyes are.

Kids, for example, are likely to have a smaller interpupillary distance to adults.

Generally, when sharing binocular microscopes, you’ll find each user will want to adjust the interpupillary distance for comfortable viewing. But this can cause problems, because each time the interpupillary distance is adjusted, the focus on the specimen is slightly affected.

However, with a Siedentopf head, this is not a concern. Each user can hold and ‘squeeze’ the head to the right fit without affecting the view of the specimen.

Siedentopf heads are therefore widely used for sharing microscopes such as in school labs.

Conclusion

You will find a Siedentopf binocular head on most modern microscopes, but not all. I’ve found a lot of Omax microscopes still use the sliding head, for example. In general, they usually lead to a better user experience and therefore are one determining factor when choosing the best microscope for your personal needs.