History of the microscope

Different types of optical microscope

Compound Microscopes, Life Science Microscopes

Generally speaking, there are two types of microscope; Compound microscopes (also known as light microscopes), which produce a mono (2D) image and stereo microscopes, which produce a stereo (3D) image. For 100% accuracy, almost all modern microscopes are compound microscope, since a stereo microscope essentially consists of two compound microscopes arranged side by side. Since we have previously discussed the different types of stereo microscope, we will now concentrate on the different types of mono, compound microscopes.

Different types of compound microscopes

There are also many variations of compound microscopes, each designed to fit a specific purpose. Whilst the optical principles of all of these compound microscopes are the same, their uses and the images the produce are often very different. Below we will outline the most popular types of compound microscope.

A note on terminology: Upright microscopes

We have already seen the terms 'compound microscope' and 'light microscope'. Both of these terms are commonly used to refer to a standard compound microscope of the type below, but are actually generic terms for any type of optical microscope. To simplify matters, some manufacturers use to term upright microscope to refer to a conventional compound microscope for use in Life Science applications, not to be different, but just to try and further clarify the type of microscope. However, terminology remains a grey area and inconsistent!

'Upright' life science microscopes

'Upright' life science microscopes are certainly the most numerous of all microscopes and are available in an infinite number of variations, ranging is size, capability (e.g. illumination techniques), performance and cost. However the most widely available versions of these microscopes are all characterised by the following features.

  • Binocular eyepieces displaying a mono image
  • High power compound objective lenses
  • Precision sample stage

The illustrated upright life science microscope (courtesy of Olympus) has a range of illumination options, trinocular head (for image capture), a precision sample stage and magnification options up to 1000x.

An endless array of upright life science microscopes with differing options and configurations are available from other manufacturers, including: Zeiss, Nikon and Leica. The result is a truly vast range of upright life science microscope, each one designed for a specific requirement.

'Inverted' microscopes

An inverted microscope is essentially an upside-down 'upright' life science microscope. This kind of microscope views objects from an inverted position than that of regular microscopes and are widely used in the study of cell cultures in liquid, since the "flat" part of a liquid sample will be the base of the liquid (i.e. the bottom of the container).

The illustrated inverted life science microscope (courtesy of Olympus) has a range of illumination options, optional image capture capability), a precision sample stage and magnification options up to 400x.

There are many other comparable systems available from other manufacturers, including: Zeiss, Nikon and Leica.

'Research' microscopes

'Research' microscope is a term used to describe high specification life science microscopes. Typically, research microscopes offer a range of advanced illumination techniques, as well as imaging software for analysing the resulting images, making them a powerful tool for high-end investigation. They also cost considerably more than 'routine' life science microscopes. 'Research'-grade microscopes may be upright or inverted, as 'research' is just a term used to describe the advanced usage.

The illustrated research microscope (courtesy of Olympus) is an upright life science microscope with advanced illumination options, automation capability with image capture and analysis solutions.

Naturally, users of research microscopes have specific requirements, so there really is an endless array of research-grade microscopes available. Other manufacturers include: Zeiss, Olympus, Nikon and Leica.

Metallurgical microscopes

A metallurgical microscope is a simple form of upright compound microscope, used to look at not only metal samples, but also plastics, ceramics and other materials. Since the samples are solid (and unable to transmit light), metallurgical microscopes tend to only have surface illumination, with high magnification options to permit the viewing of surface structure (to identify metal fatigue, for example).

The illustrated metallurgical microscope (courtesy of Olympus) is a compact microscope equipped with all the functions required for metallurgical observation, with magnification options up to 1000x and image capture options. Other comparable systems are available from many other manufacturers, including: Zeiss, Nikon and Leica.

Measuring microscopes

Measuring microscopes are essentially compound microscopes with a high precision measuring stage. A cross-hair is displayed in the eyepieces, enabling accurate point to point (X,Y-axis) measurements to be made. Measurements in the Z-axis (vertically) are possible by differential focus - focusing on one plane and then refocusing on another plane. The small depth of focus with high magnification objective lenses ensures accurate results. Measuring microscopes are typically used to check the dimensions of precision manufactured parts (for quality control) and provide measurement accuracies of up to 1 micron (0.001mm).

The illustrated measuring microscope (courtesy of Mitutoyo) is a simple model capable of routine measurements.

Other more advanced measuring microscopes are available from Vision Engineering, Olympus and Nikon.

Digital microscopes

Digital microscopes may not technically be microscopes; however they are becoming more widespread so are worth a mention. Like the optical microscope, there are a huge number of options and configurations of video microscopes, from simple digital microscopes to advanced video measuring systems, however digital microscopes should certainly not be viewed as a replacement for the optical microscope, rather just another type of device which provides some different options in certain situations.

Digital microscopes provide simple imaging, convenience for electronic image capture and can be very inexpensive, so can be used for lower magnification tasks as an alternative to a stereo microscope (although the digital image will be 2D). Higher magnification digital microscopes are also available which aim to provide a direct alternative to the compound microscope.

History of the microscope