Microscopes enhance our sense of sight – they allow us to look directly at things that are far too small to view with the naked eye. They do this by making things appear bigger (magnifying them) and at the same time increasing the amount of detail we can see (increasing our ability to distinguish between two objects or ‘resolve’ them). For this reason, they are one of the most widely used tools in science.
Different kinds of microscopes can show us different amounts of detail (they have different resolving power). Electron microscopes have a far greater resolving power than light microscopes, so we can use them to see even more detail than is visible under a light microscope
Microscopes magnify and show more detail
When we talk about how microscopes work, we often say that they make things look bigger – that is, they magnify them. We describe what we see down the microscope in the same way, for example, we might say that the dead fly we’re looking at has been magnified 200 times. This helps us to make sense of what we’re seeing. It also helps others who are looking at our photographs or drawings to understand what they’re looking at. This is why all micrographs published in scientific journals must indicate the extent of magnification.
However, making things bigger is only part of the story. If microscopes did nothing but make what we can already see bigger, they wouldn’t be much use! Instead, microscopes increase the amount of detail that we can see. Another word for the level of detail we can see is ‘resolution
To understand the difference between magnifying something and increasing the detail that’s visible, have a look at this digital photo of harakeke. Explore further the big science ideas of magnification and resolution.
Thinking about resolution
Scientists think of resolution as the ability to tell that two objects that are very close together are distinct objects rather than just one. The naked eye can tell apart (resolve) two objects (such as grains of sand) that are about a tenth of a millimetre apart – any closer than that, and we see the two as a single shape. If we look under a light microscope on the highest magnification, we can distinguish between objects that are less than a micrometre (a thousandth of a millimetre) apart. If we try to magnify further, we won’t be able to see any more detail than this – just like the digital photo above, the microscope will have reached the limit of its resolution.
Understanding the limits of resolution
Scientists have worked out why we can’t see an unlimited amount of detail down a microscope. They found that any object that’s less than half the wavelength of the microscope’s illumination source is not visible under that microscope. Light microscopes use visible light (which has a minimum wavelength of 400 nm, or less than one thousandth of a millimetre). This means that we will never be able to see any object smaller than approximately 200 nm (about the width of an average-sized bacterium) using a light microscope (and in practice, many light microscopes can’t get close to this resolution because of lens quality).
Even more detail: using electrons instead of light
Understanding the limits of light microscopy led to the development of the electron microscope. In the same way that light has a wavelength, the movement of high-speed electrons also has a wavelength. The wavelength of electrons is thousands of times shorter than visible light, so scientists predicted that electron microscopes would be able to resolve objects that are thousands of times smaller. They were right – there are now electron microscopes that can detect objects that are approximately one-twentieth of a nanometre (10-9 m) in size. This means that electron microscopes can be used to visualise viruses, molecules and even individual atoms.
The wavelength of electron movement is measured in picometres (billionths of a millimetre), so electron microscopes should in theory be able to visualise even smaller objects than they currently can. The resolution is currently limited because of technical aspects of viewing samples, but it may eventually be possible to view objects at the theoretical resolution limit of electron microscopes.
Scientists use a series of conventions when labelling microscope images. They include information about the magnification of the image (for example, 600x) as well as a scale bar, which acts as a ruler and indicates the true size of the object. These conventions help others to make sense of the images.
Try zooming in on images of famous paintings. The high resolution of the photographs lets you see extraordinary detail.
Find our more about how resolution limits affect what can be seen using satellite imaging.
The light intensity decreases as magnification increases. There is a fixed amount of light per area, and when you increase the magnification of an area, you look at a smaller area. So you see less light, and the image appears dimmer. Image brightness is inversely proportional to the magnification squared.
What do you adjust when on the highest power on a microscope?
When you switch to a higher power, the field of view is closes in. You will see more of an object on low power. The depth of focus is greatest on the lowest power objective. Each time you switch to a higher power, the depth of focus is reduced.
How do you adjust a light microscope?
Locate the eyepiece, which extends diagonally toward you. Look through the eyepiece as you adjust the knobs. Turn the coarse adjustment knob (the larger one) so that the objective lens moves upward and away from the slide in centimeter increments until the image comes into focus.
What happens to the brightness of the view when you go from 4x to 10X?
While viewing the letter “e” under a compound microscope, how is it oriented? What happens to the brightness of the view under a compound microscope when you go from 4X to 10X? it gets dimmer. How to calculate magnification when using a compound microscope?
Is it better to increase or decrease the light when changing to a higher magnification?
In general, the more light delivered to the objective lens, the greater the resolution. The size of the objective lens aperture (opening) decreases with increasing magnification, allowing less light to enter the objective. You will likely need to increase the light intensity at the higher magnifications.
Which objective lens has the smallest field of view?
4x objective lens
The 4x objective lens has the lowest power and, therefore the highest field of view.
What is optimal lighting level on microscope?
4x objective = Aperture of iris should be nearly closed to 1/8 open. 10x objective = Aperture of iris should be somewhere between 1/8 – 1/4 open. 40x objective = Aperture of iris should be somewhere between 1/4 – 1/2 open. 100x objective = Aperture of iris should be somewhere between 1/2 – 3/4 open.
What happened to the letter E when it was observed under a microscope?
– The letter “e” – The viewing of this familiar letter will provide practice in orienting the slide and using the objective lenses. The letter appears upside down and backwards because of two sets of mirrors in the microscope.
How should you cut a biological specimen?
Animal & Plant Tissues – these samples are sectioned by cutting them with a razor blade or the use of a microtome so they can be placed flat between a slide and cover slip and viewed under a biological microscope. Advanced microtomes can provide samples as thin as 1 micrometer. Hand-cut samples are typically thicker.
What happens when you go from low power to high power on a microscope?
When you change from low power to high power on a microscope, the high-power objective lens moves directly over the specimen, and the low-power objective lens rotates away from the specimen. This change alters the magnification of a specimen, the light intensity, area of the field of view, depth of field, working distance and resolution.
How can I increase the light intensity of a compound microscope?
Some microscopes have a recessed dial that is rotated to the right to increase the intensity and to the left to decrease light intensity. Depending what type of illumination your compound microscope has, you may need to use a daylight balancing filter .
How do you adjust the magnification of a microscope?
Turn the fine adjustment knob until the specimen comes into sharp focus. Caution: should not take a long time to find focus, otherwise the high magnification objective could also hit the slide. If you are having a difficult time to find focus then restart with the lower magnification objective.
What’s the best way to focus a microscope?
Set your microscope with the lowest power objective. Place the slide on the stage, and looking from the side, bring the objective as close to the slide as possible. Looking through the microscope, focus away from the specimen until the image comes into focus.