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What Is A Camera? The 3 Main Components

If you are reading this there’s a very high chance that you’ve either seen a camera or used one. But how do you actually define what a camera is? 

Well it can get quite technical but we’ll try to define it simply for you into 3 separate components: 

  • Lens
  • Body
  • Sensor / Film

Let’s start with the lens:


The lens of a camera is the optical element of the camera system and is what allows light into the camera to be directed and focused onto the sensor/film. 

Lenses can be very complex in construction and there will never be a one size fits all lens.

For example, a lens designed for a high level of zoom for wildlife photography probably wouldn’t be used by a studio photographer and vice versa. 

This is why lenses can vary so much in quality and design, but you will probably find a lens that matches your use.

Just remember that you can only make use of different lenses if your camera uses an interchangeable lens system.

Some cameras will have one fixed lens which you can’t swap – think of your smartphone or a point and shoot camera.

On the other hand, interchangeable systems like DSLRs and mirrorless cameras give you the option of changing lenses to match your shooting style. 

Now let’s look at some basic things to consider for a lens:

Focal length

The focal length of a lens is measured in mm (millimetres) and it affects the angle of view and magnification of an image. 

The angle of view is just how much you can see in one frame.

So a wide angle of view will let you get more into a picture compared to a narrow angle of view.

Here’s an easy way to remember:

The higher the focal length the narrower the angle of view and higher magnification.

By magnification we just mean zoom. 

So let’s say that you are standing at a specific spot; a 100mm lens would be much more zoomed in and have a narrower angle of view so you would get less in a scene from that spot compared to a 30mm lens.

You would also be much more zoomed in with the 100mm lens.

The focal length is also shown in terms of its 35mm film equivalent. This is the equivalent of it being on a full frame camera and is used as a standard.

We need this because the effective focal length of a lens can change depending on what camera it is on. 

Here’s why: 

On a crop sensor camera the focal length will be multiplied by its crop factor for that camera. 

Related Reading:

Another thing to consider about focal lengths is whether the lens is a zoom or prime lens. 

A zoom lens may have a range of focal lengths that the lens can work at, e.g. 24-70mm, so this way you can cover different focal lengths in this range.

On the other hand a prime lens will have a fixed focal length, e.g. 50mm, so you can only ever have one angle of view with that lens.


Aperture is really important to know.

An aperture is the opening in the lens which lets light into the camera.

On each lens the aperture value is denoted by an f-number (e.g. f/1.8) and it determines how big the opening is, which in turn determines the depth of field and how much light is let into the camera. 

This is the confusing part:

A smaller f-number = a bigger opening. 

E.g. f/1.8 causes a bigger opening than f/16.

Lenses will normally be advertised with their maximum aperture and this will tend to be a low f-number like f/1.8 or f/4. 

Prime lenses will have one maximum aperture value. 

Zoom lenses may have different maximum apertures at different focal lengths since they are more complicated in design. 

So zoom lenses they may be shown with a range of apertures such as f/3.5-5.6.

For now we won’t go into too much detail, but in general the lower the f-number on a lens the better quality it will be and the more expensive it will be. 


Lenses also have varying technologies for focusing. Examples of auto focus systems include “stepper motor” and “ultrasonic motor”.

These motors are normally driven by the camera body. 

Each brand tends to have their own acronym for these technologies too, but you will always have some sort of manual focus ability on your lens too. 


Nowadays image stabilisation is really advanced and different camera companies have various acronyms for their own technology of image stabilisation. 

These systems allow the lens to compensate for small amounts of movement or camera shake to take sharper photos.

This can be very useful especially when you need to use a slower shutter speed due to a lack of light. 


The body is what connects your lens to your sensor or film and it stops any unnecessary light entering unless it is through the lens.

In modern digital cameras, the body is basically the brain of everything and effects a lot of the settings and capabilities of the camera. 

Here are some things to consider: 


The body will control the shutter which determines how long one exposure is through the shutter speed you set. 

This is basically how long the film or sensor is exposed to light and this is a major component in getting the exposure right on a photo. 

Light meter

A light meter is a device that measures light and it is used in a camera body to help in determining how to expose a photo.

This is needed especially for auto modes on a camera since the camera has to try and compute what the right settings are under different lighting conditions.

Focus detection

In camera bodies there will be some sort of focus detection to help drive the auto focus motor in the lens and there are different types of technology for this.

Contrast detection and phase detection are the types of autofocus detection used in cameras, but it differs from camera to camera.

It used to be the case that DSLRs were undoubted kings in this field, but recently mirrorless cameras have been catching up in performance.

Image storage

In film cameras the film itself will be moved so the next frame is ready to be exposed. 

In digital cameras the camera will simply convert the information that the sensor takes in and store that as an image on the SD card. 

If it is a raw file it will store it without changing the data.

However, if you choose to shoot only JPEGs then the camera will have to quickly convert the RAW file into a JPEG before storing it. 


The viewfinder is the rectangular eyepiece that you can look through to frame your photo.

In DSLR’s you will have an optical viewfinder (OVF) whereas on mirrorless cameras you would only have an electronic viewfinder (EVF).

Other cameras may have just a screen instead of any viewfinder in the form of an eyepiece.

Think of your smartphone, it just has a screen which will show you the preview of your picture that you are framing. 

The last component to consider is the photosensitive surface:

Sensor / Film

When the light has entered the camera through the lens it is focused on to either an image sensor or film. This is where the photo is produced. 

Without getting into too much detail, it’s just a way of converting the light rays into an image. 

We will look at sensors and the 2 main things to consider. 


The resolution is normally advertised in MP which stands for megapixel (1 million pixels).

In general the higher the pixel count, the better the camera. This is because it should be able to record more details with a higher pixel count.

However sometimes this can be misleading because the size of the sensor counts too. 

For example, a 24mp sensor on a smartphone is not the same as a 24mp sensor on a DSLR since the DSLR sensor will be larger.

Sensor size

Size matters. Bigger sensors are going to perform better than smaller sensors if everything else is kept equal. 

Larger sensors will tend to have better performance when it comes to dynamic range and ISO noise. This is to do with how pixels are spaced out.

Another reason to consider the sensor size is the crop factor which affects the equivalent focal length. 

The following blog post explains these concepts relating to sensor size in more detail.

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We hope you found this helpful! As always we appreciate your time for reading this.
– Photography Pursuits Team