Microscope barlow lenses explained

Barlow lenses explained

Named after English mathematician Peter Barlow, a Barlow lens is simply an extra lens you fit over your microscope to increase or decrease the magnification.

Having the option to adjust your magnification on the fly can be very handy – it increases the range of magnifications you have access to without needing to buy new eyepieces or a new microscope.

But the real value of a Barlow lens lies in what else you can change when you alter your magnification – the field of view and the working distance.

When would you use a Barlow lens?

The two main reasons to use a Barlow lens are to give yourself more room to work in or to get a bigger field of view.

A microscope at a certain magnification focuses at a particular distance from the lens. Often this isn’t a problem. It doesn’t matter how close the lens is to your sample – you’re looking through the microscope after all.

But what if you want to see your entire sample at once, rather than just a small section of it? Or need to fit a soldering iron between the lens and a circuit board?

Enter your handy barlow lens.

When you fit a reducing barlow lens onto your microscope you lower the magnification, but you increase the field of view and the focal distance between the lens and your sample.

In practical terms, you’ll be able to see more of your sample and you’ll have more space to work in.

Barlow lenses can either reduce or increase magnification, so you can adjust your field of view and working distance to best suit the task at hand. They’re also very easy to attach or detach, so they won’t slow down your work.

Popular uses

Barlow lenses are generally used on stereo microscopes.

Stereo microscopes have relatively low magnifications – often between 5x and 50x – and are used to look at larger objects and specimens, such as electronics, plants, animals or geological samples. They are also quite limited in their range of magnification – some have a single magnification setting, some have two, and others can variably zoom within a set range.

Between their limited magnification range and the hands-on nature of microscopy, some industries and fields can benefit greatly from Barlow lenses.

Variable-sized samples like rocks or circuit boards can be easily catered to by increasing or decreasing the magnification to best suit the situation. Similarly, if more working space is needed for electronics repairs or dissection, then simply attaching a reducing Barlow lens will give you all the room you need to work without hindrance.

Barlow lenses also have a limited use with compound microscope eyepieces to increase the magnification, but this often causes more problems than it solves.

0.5X Barlow Lens


Barlow lenses are a useful and versatile option for anyone using stereo microscopes. They’re particularly useful if you do any hands-on work under the microscope and can improve the ergonomic of your workplace.

They’re a relatively cheap way of changing your magnification, field of view and working distance, and take very little time to set up. Prices usually range from $75 to $200 at most reputable sellers.

Tip: It is critical that you select a Barlow lens with a barrel size that will fit your specific microscope.

Previous article Which is the best microscope for soil analysis
Next article Microscopes for primary schools