A Simple Guide to Magnification

Magnification is defined as the size of an image compared to the object’s size. In day to day surroundings, Mirrors and lenses can magnify images. To calculate magnification given by a lens can be calculated with the help of the formula given below.          

Magnification= Image height/ Object height

Because magnification is a ratio between two lengths, it does not have units. However, both the image height and the object height must be taken in the same unit, e.g. either centimetre (cm) or millimetres (mm). It should not be a combination of the two. Some optical instruments such as magnifying glass, telescopes, microscopes, and slide projectors provide visual assistance by magnifying small or distant subjects.

Explanation of the formula

In order to understand the application of the formula to give the magnification of the lens, Let us understand with the help of an example:

Question: An item that is 2 cm tall makes an image that is 250 cm tall. Calculate the magnification.

Answer: Since, magnification= Image height / item Height

Therefore, magnification= 260/2 = 130( magnified)

Transverse magnification and angular magnification

For real images that are visible on a screen, the measured size means a linear value in millimetres or inches.

Whereas, optical instruments with an attached eyepiece, the linear value of the seen image, which in reality is the virtual image in the infinite distance, cannot be produced. Therefore the angular size is the measured size that can be defined as the angle extended. We can alternatively say, subtended by the object at the focal point. Therefore, angular magnification’s formula is:     

MA = tan Ɛ / tan Ɛ0 

Where Ɛ is the angle given by the object at the focal point in the front. Ɛ0 is the angle given by the image at the focal point(rear) of the eyepiece. By default, for optical microscopes and magnifiers, where the size of the object is a linear value and the evident size is an angle, the magnification is defined as the ratio. This ratio is between the visible size ​(angle) seen in the eyepiece and the object’s angular size. This can be located at the nearest distance, which is 25 cm from the eye.

Maximum usable magnification

There is a maximum magnification in any telescope, microscope, or lens. There are no more details beyond the point where the image is seen larger. One can say that the magnifications beyond this maximum point are known as “vacuum magnification”. 

When good quality telescopes are operated in a suitable atmosphere and environment, diffraction resists the maximum usable magnification. In practical terms, a 60 mm telescope has a magnification of 120 * in practical terms; mathematically, it is the same as 2 * aperture in millimetres or a 50 * aperture in inches. The best resolution possible for optical microscopes using high-aperture optical instruments and using oil immersion is 200 nm, which translates into about 1200 times magnification. A maximum magnification of 800 * is possible without oil immersion. Small, inexpensive telescopes and microscopes often feature eyepieces that can provide a considerably higher magnification than necessary.

Magnification produced by convex lens

A convex lens can form both images, i.e., virtual and real images. Therefore, in the case of a convex lens, magnification can give either positive or negative magnification. In the case of a virtual image, the value of the magnification is positive. The value is negative in the case of a real image.

the image is magnified when |m|>1,

The image is diminished when |m|<1,

The image is of the same size as that of the object when |m|=1. 

Magnification produced by concave lens

Concave lenses give virtual images, always. Therefore the magnification value of a concave lens is always positive. A concave lens always makes the image smaller than the object. That is why |m|<1.

Conclusion

It can be concluded from the above information that magnification is the process of enlarging the evident size visible. In practical terms, when the calculated magnification number is less than one, it is known as a reduction in size. It is known by other names, such as minification or de-magnification. Simply put, the act of making something look larger than it actually is known as magnifying. It makes the more prominent appearance of an object when it is seen through an instrument such as a microscope, telescope, etc. It is not possible to adjust the magnification of the mirror for 5x magnifying, for example, as the magnification is built in.