Define and explain focal length, basic characterization of a photographic lens


Focal length, generally expressed in millimeters (mm), this is the basic characterization of a photographic lens. It is not a measurement of the certain length of a lens, but this approach does not measure an optical distance, where the ray of light is to create a sharp image of an object in a digital sensor or a 35 mm film on the focal plane in the camera. When the lens focuses on infinity, the focal length of a lens is fixed.

Focal length tells us the perspective of view, how much the scene will be captured, and its greatness – how many major elements are. The focal length, narrow, perspective view, and more. Low focal length, wide-angle view, and low magnification.


There are two kinds of lenses-prime and zoom. Prime lenses contain a fixed focal length and zoom lenses contain Polaris focal lengths. The convenience of the zoom lens is its utility. They are ideal when you are photographing a quality of places such as landscapes and portraits, and you just want one lens for both conditions. Utilizing a zoom lens also diminution the number of times you need to change the lens which saves time and extends the possibility of getting dust in the camera’s mirror box or on the sensor.

The main convenience of prime or fixed focal length lenses is their size and weight as well as their upper limit aperture or. Prime lenses incline to be more compact and lightweight than zoom lenses.


Prime lenses also inclined to have a larger upper limit aperture (f/1.4 to 2.8). This is a convenience when shooting in low light conditions as it will alteration the possibility of hand holding the camera and freezing the subject without shake or blur caused by the longer disclosed. Photographing utilizing prime lenses with large apertures also means you can get a shoal depth of field which is useful for portraiture where you might want a delicate or blurred background (also known as bokeh).

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Formula for finding focal length

There may be different formulas for finding Focal length, but the easiest and mathematical way of finding Focal length I’m going to discuss here.

First of all, you have to understand the symbol of Focal length and height of an object then it will be easy to solve the required equation for finding focal length.

1/f=1/object distance +1/image distance

Another equation which relates to solving the Equation, I’m going to discuss the formula of magnification.

Magnification=height of object/height of image


image distance/object distance.

The mentioned above formulas are used to calculate the magnification and focal length.

If you understand the physics as well as its equations and know how to solve equation then it’s easy to understand the Given Equation.