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How Do Cameras Work? A Guide for Beginners

how do cameras work? a guide for beginners

Want to know how cameras work but don’t want to read about complicated mathematics and physics? This is the guide for you.

In this article, I’ll explain how most cameras work, and I’ll also explain the differences between various camera types (such as film versus digital and DSLR versus mirrorless). With this knowledge, you can make an informed choice before buying a new camera – plus, you can better understand what’s going on inside your equipment!

If you’re ready to get started, let’s dive in.

How do cameras work? The basics

If you look at the giant cameras used by photography pioneers, then you check out the latest iPhone camera, you might think they don’t have anything in common.

But in reality, the basic concept of how cameras work hasn’t changed much. Put simply, the light reflected from the subject goes into the camera through a hole; it’s then projected on the back of the camera, where it’s registered by a light-sensitive material (whether a digital sensor or film).

This core process has stayed the same since the invention of photography, though the details have changed. Let’s start at the very beginning, then build up to modern-day camera equipment.

The camera obscura

Camera obscura
Source: Wikimedia Commons

The forefather of the photographic camera was the camera obscura, first created in 1545 based on a principle that dates back to around 400 BCE.

The first camera obscura was just a dark room with a hole in one of the walls. Whatever was outside of the room would be projected through the hole onto the opposite wall. Because light travels in a straight line, the projection would be upside down, as you can see in the diagram above.

Over time, the camera obscura became smaller – instead of whole rooms, it was made from boxes – and was used to aid artists when drawing.

The pinhole camera

Pinhole camera - How do cameras work
Source: Wikimedia Commons

A camera obscura is just a box with a hole that allows light to project on the opposite side – but once you add in a light-sensitive material, you have a pinhole camera.

It’s a simple item you can create with a shoebox (or any box) painted black. Use a needle or a pin to punch a small hole, then place a negative film or a sheet of photographic paper at the back to register the image projected inside.

In essence, this is how any photographic camera works, even the latest models. Of course, some elements have evolved, as I explain in the next section:

Photographic cameras

simple DSLR diagram
The basic DSLR components.

All cameras, old and new, work under the same principle: light comes through a hole and projects an image on the back of the camera. But different models feature various details, and I can’t go into all the developments, so please bear with me as I talk generically.


Unlike pinhole cameras, most current cameras have a lens. Lenses generally include multiple glass elements that bend the light for a sharp, focused image.

The quality of the glass, the way it’s arranged, and the amount of glass inside the lens can impact the quality of the final image. This is one of the reasons why some lenses are more expensive than others.

By moving the lens glass, you can focus the image. And in some (zoom) lenses, you can also change the focal length.


Modern lenses contain an aperture, a hole that allows in light. In most cameras, you can control the size of the aperture, much the same way as the pupil in our eyes dilates or contracts to let in more or less light.

The lenses that allow for wider maximum apertures are more expensive and are commonly known as fast lenses. Note that the aperture is expressed in f-numbers, like so: f/1.8, f/2.8, f/6.3, f/9, f/16, etc., where smaller f-numbers correspond to larger apertures.


As light moves through the lens toward the camera body, it won’t simply impact the camera sensor or film. There’s a barrier that opens and closes to block the light or allow it through, called the shutter.

Most shutters consist of two curtains. When you press your camera’s shutter button to take a photo, the first curtain slides up to expose the sensor or film to light. Once a predetermined amount of time has passed (the shutter speed), the second curtain covers the sensor or film, and the image-making process stops.

Film/Sensor and ISO

When light reaches the back of the camera, it gets recorded by the film (analog cameras) or the sensor (digital cameras).

I won’t go into much detail here, because I’ve discussed this in depth down below. I will tell you, however, that films and sensors can have different sensitivities to light, called ISO (or ASA).

By the way, ISO is the third factor you need to consider when exposing a photograph. The ISO, along with the aperture and the shutter speed, form the exposure triangle.

Film vs digital cameras: what’s the difference?

many types of cameras

These days, digital cameras are far more popular than film cameras – yet some photographers still prefer film, and the technology is more similar than you might think.

The main difference between film and digital cameras is the medium that registers the image. Digital cameras have a sensor that stores the image as data, while analog cameras use photosensitive film.

A digital camera uses one sensor – once the camera is built, there’s no changing it. But analog cameras offer all sorts of film types. You can load a traditional camera with negative film (black and white or color), slide film (also known as color reversal and black and white reversal), or infrared film.

Of course, before you load an analog camera, you’ll need to decide which type of film you want to use, how sensitive it should be (the ISO/ASA), and how many pictures you want (conventional film rolls offer 12, 24, or 36 exposures).

You can make some changes afterward, such as pushing or pulling the film, as well as cross processing. However, these changes affect the entire roll and not a single photo.

With digital cameras, you can change nearly every setting from image to image: the ISO, image quality, file format, and whether the shot is in color or black and white.

Photographic film comes in different sizes (35mm, 120mm, 4×5, etc.). In the same way, you can find different digital sensor sizes; I’ll talk more about them in a later section.

Let me emphasize that film is not better than digital or vice-versa. It’s a matter of personal preference, style, and storytelling.

Types of digital cameras

Photographers use many different camera types, but for the purposes of brevity, I’ll skip the large- and medium-format cameras and focus only on the most common options.


Canon DSLR camera with lens

DSLR stands for digital single-lens reflex, which is the digital counterpart of the popular SLR film camera. DSLRs use interchangeable lenses, and the lenses from a DSLR often work on an SLR and vice-versa.

The most distinctive characteristic of the DSLR is a reflex system that allows you to see exactly what you capture through the viewfinder. On the outside of the camera, you’ll notice a bump, beneath which sits a series of mirrors. On the inside, the light that comes through the lens hits a mirror in the back of the camera. This mirror is positioned at such an angle that it reflects the light up toward a pentaprism, where it bounces to reach the viewfinder.

When you push the shutter button on a DSLR, the mirror flips up to let the light pass through to the sensor. That’s why, during a DSLR exposure, you can’t see anything through the viewfinder.

Mirrorless cameras

Olympus mirrorless camera

As the name suggests, mirrorless cameras don’t have a mirror in front of the sensor.

Mirrorless cameras are relatively new, and prior to the last few years, they were considered amateurish because the quality didn’t match that of a DSLR.

Nowadays, mirrorless cameras have full-frame sensors just like DSLRs, so the main difference is the size – mirrorless cameras tend to be far smaller than DSLRs – and the viewfinder. You see, because mirrorless cameras don’t feature the mirror used by DSLR technology, there’s no “true” viewfinder image; instead, higher-end mirrorless cameras offer a feed to the camera sensor (so you can preview the image), while some entry-level cameras don’t have a viewfinder at all. (In the latter case, you can preview the image on the rear LCD screen.)

Optical viewfinders (DSLRs) and electronic viewfinders (mirrorless) offer various advantages and disadvantages. I won’t get into the details here, but suffice it to say that both work great for pro-level work, and you can rely on either option for beautiful results.

Bridge cameras

Bridge cameras are often called “superzoom cameras,” because they generally feature a wide range of focal lengths – though unlike DSLRs, you can’t swap out the lens.

And while bridge cameras are built like DSLRs, they usually don’t have an optical viewfinder.

The sensor is often small, and to this day, there aren’t any full-frame bridge cameras. In fact, bridge cameras are halfway between a DSLR and a point-and-shoot camera – hence the name, “bridge.”

Point-and-shoot cameras

Fujifilm point and shoot camera

Point-and-shoot cameras, also known as compact cameras, may offer some manual control – but they’re meant to be used in Auto mode, and they’re all about ease of use. You simply point the camera, press the shutter button, and get a photo.

Point-and-shoot cameras have a fixed lens, and while they’re quite small in size, they have become somewhat irrelevant as smartphone cameras have advanced in power and popularity.

Camera sensors: why do they matter?

Photographic camera sensor

In the back of every digital camera is a sensor that records light, and you see the result as a digital photo.

A camera sensor is a grid of photosites that capture photons and convert them into a voltage value. This information is later processed in different ways according to the type of sensor – currently, they can be CCD or CMOS, although CCD is becoming less common.

Each photosite is called a pixel (sensel is a more technical term, but this article is meant to be an introduction, so I’ll stay with the commonly used pixel).

When you see that a camera has 24 megapixels, it produces images formed by 24 million pixels. Don’t be tempted by a high pixel count, though. You’ll have bigger images, yes – but they won’t necessarily be better. Let me elaborate.

Megapixels and image quality

If all camera sensors work the same way, then what’s the difference? Why should you buy one camera sensor over another? The main reason is that sensors come in different sizes, and so different sensors have different-sized pixels.

Have you ever wondered why some smartphones have 108 MP and professional cameras only have 30 or 40 MP? It’s because the pixels in that 108 MP smartphone are tiny, whereas the pixels in a 30 MP full-frame DSLR are much larger. Most people know about megapixels and think that more MP equals better image quality, so smartphone camera manufacturers keep increasing the pixel count, but this isn’t always a good thing.

How do the sensor size and pixel size impact your photography?

  • Bigger pixels (usually found in bigger sensors) have a better high-ISO performance (though note that newer cameras generally offer better high-ISO performance over older cameras, so a small, new sensor may be superior to a large, old sensor).
  • At high ISO values, small pixels lose significant dynamic range.
  • Larger sensors feature a shallower depth of field than smaller sensors, assuming the image is identically framed. This can be an advantage or a disadvantage depending on your needs.
  • Smaller sensors mean that you have to apply a crop factor to your lens, effectively giving it a longer focal length. For example, a standard 50mm lens on a full-frame camera becomes a 75mm telephoto on a standard APS-C camera. Again, this can be good or bad depending on what you want to shoot.

Sensor sizes

Sensor size comparison how cameras work
Source: Wikimedia Commons

Sensor sizes aren’t standard, and you’ll find that each manufacturer makes their own rules. However, here are some categories that you can use as a starting point:

Medium format: Only certain professionals use sensors this big, so I won’t go into too much detail. However, it’s important to know they exist. The sensor sizes range from 43.8 x 32.9 mm to 53.7 x 40.2 mm.

Full frame: These sensors are the equivalent of 35mm film, which is 36 x 24 mm. It’s the standard size found in professional DSLRs and mirrorless cameras.

APS-C: These are commonly referred to as cropped sensors, because they’re cropped in comparison to full-frame sensors. The size varies according to each brand, but many manufacturers, including Nikon, Sony, and Pentax, use 23.6 x 15.6 mm, while Canon uses 22.3 x 14.9 mm.

Four Thirds/Micro Four Thirds: This standard was created by Panasonic and Olympus so that lenses could be compatible across brands. The size is 17.3 x 13 mm.

Sensors used in bridge cameras, point-and-shoot cameras, and smartphones are less consistent in size, but they are generally smaller than the Four Thirds standard.

How cameras work: final words

As you can see, cameras can be complicated! But hopefully, you now have a better understanding of how cameras work, and you know how to pick a camera of your own.

Now over to you:

Do you have a favorite camera type? Do you shoot with digital or film cameras? Share your thoughts in the comments below!

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Ana Mireles
Ana Mireles

is a photographer and artistic researcher. She has been awarded and exhibited in Mexico, Italy, and the Netherlands. Through theory and practice, she explores the cultural aspect of photography, how it helps us relate to each other, the world, and ourselves. She has also a passion for teaching, communication, and social media. You can find more about her and her work at her website or acquire some of her works here.

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