Inside the Camera: A Complete Guide to Structure and Function

Unlock the secrets of digital cameras with an in-depth look at their essential components. Explore each part’s unique role in capturing stunning images and enhancing your photography skills.

Author: Marco Crupi

This article is a segment of the Digital Photography Course. Click here to return to the main course overview.

In a previous photography course article, I explored the different types of digital cameras. Now, let’s dive into the basic components and operation of a DSLR.

The operation of a digital SLR camera is complex, but it can be simplified without delving into overly technical details not relevant to this course. Light (illustrated by the yellow arrow in the diagram above) enters through the lens and is reflected by the mirror up into the pentaprism (or pentamirror in more budget-friendly models), allowing you to see the scene through the viewfinder. When you press the shutter button, the mirror flips up, and the shutter curtain opens, letting light reach the sensor and capture the image. This process will be discussed in more detail in the following sections of this article.

In mirrorless and compact cameras, since there is no mirror or pentaprism, the operation is slightly different – the light hits the sensor directly.

Below, I will analyze in detail the individual components of a digital camera.

A lens can either be permanently attached to a camera, as seen in compact and bridge models, or be interchangeable, allowing you to swap it with other lenses that offer varying focal lengths, apertures, and unique features.

The light entering the lens is regulated by the diaphragm, a circular or polygonal mechanism made up of thin metal blades.

For an in-depth look at the diaphragm and different types of photographic lenses, check out my article: The Ultimate Guide to Choosing the Right Camera Lens.

SLR (Single Lens Reflex) cameras are named for their unique viewing system, which consists of a mirror set at a 45° angle relative to the lens and a pentaprism or pentamirror.

The mirror reflects light passing through the lens, allowing the image to be seen through the viewfinder. The pentaprism’s role is to correct the orientation of the image, which would otherwise be reversed left to right. During the exposure, the mirror flips up to allow light to reach the sensor; in this raised position, the mirror blocks the focusing screen, preventing stray light from entering through the viewfinder. This mechanism ensures that the photographer sees the exact image that will be captured by the lens.

As previously mentioned, compact, bridge, and mirrorless cameras lack this optical viewfinder system. In these models, light passes directly through the lens to the sensor. The scene is then viewed on the rear LCD screen and, if available, through an electronic viewfinder.

The absence of the mirror and pentaprism/pentamirror provides several benefits, including the ability for manufacturers to design smaller and lighter cameras, faster autofocus, higher continuous shooting speeds, and the elimination of micro-vibrations caused by mirror movement, which can introduce slight blurring during long exposures.

The only notable drawback of mirrorless cameras compared to SLRs is their higher energy consumption, which results in shorter battery life.

The shutter is a mechanism that controls the duration for which the sensor is exposed to light, adjusted via the camera’s shutter speed settings. It typically consists of two fabric or metal curtains positioned parallel to the focal plane. When activated, these curtains move vertically to create a slit that allows light to reach the sensor.

I will cover shutter speeds in detail in a dedicated article.

With technological advancements, the traditional shutter mechanism is gradually being phased out. A notable example is the Sony Alpha 9 III, which replaces the conventional shutter with a “Global Shutter” technology.

The viewfinder is a device that allows photographers to preview the scene they are framing.

In digital cameras, there are two types of viewfinders: optical and electronic.

Optical viewfinders are used in SLR cameras (both digital and analog). Due to cost considerations, only high-end professional models offer a 100% view of the framed scene. In entry-level and semi-pro models, only about 90-95% of the field is visible, which means some parts of the scene may not be seen through the viewfinder.

The electronic viewfinder (EVF) is found in mirrorless and other non-SLR digital cameras. It consists of a small display that shows a real-time preview of the scene captured by the sensor.

Using the rear display is referred to as Live View mode. In this mode, light hits the sensor directly, and the data is processed by the camera’s CPU before being displayed on the rear screen. In SLRs, when Live View mode is activated, the mirror is raised, preventing light from reaching the optical viewfinder.

Choosing a camera with an articulated rear LCD display is highly recommended, as it provides greater flexibility in various shooting scenarios. For example, at concerts, you might need to take photos with the camera held above your head—an adjustable screen tilted downward makes framing much easier. Conversely, when shooting low to the ground, the ability to tilt the screen upward is invaluable.

LCD screens can be difficult to view in bright light. For this reason, some mirrorless cameras include a small optical viewfinder (OVF) or an electronic viewfinder (EVF) to help with framing.

Viewfinders: Optical vs. Electronic

With SLRs, the scene is viewed directly through the lens, showing the actual view of the subject. Any changes to settings are visible only after the shot is taken. Mirrorless cameras, however, provide a constant live preview of the scene, reflecting all adjustments in real time, allowing photographers to see exactly how the photo will turn out before pressing the shutter.

Before the rise of digital technology, images were captured on film. Today, in modern digital cameras, the sensor plays a crucial role.

The most commonly used sensors in cameras are CCD (Charge-Coupled Device) and CMOS (Complementary Metal-Oxide-Semiconductor). Another type, the FOVEON sensor, is currently exclusive to Sigma cameras.

CCD and CMOS sensors each have distinct characteristics and applications:

• CCD sensors offer superior image quality and produce less noise compared to CMOS sensors.
• CMOS sensors consume significantly less power than CCD sensors.
• CMOS sensors are more cost-effective to produce than CCD sensors.ù
• CMOS sensors allow for faster continuous shooting.

Due to these characteristics, CMOS sensors have become widespread in compact cameras and smartphones, while CCD sensors were traditionally used in cameras that prioritize high image quality. However, as technology has advanced, the gap between CCD and CMOS has narrowed significantly. Today, CMOS sensors are commonly found in mid- to high-end cameras, offering a balance of performance, efficiency, and cost.

What are Megapixels?

A sensor’s resolution is measured in megapixels. In digital photography, one megapixel equals one million pixels. The term refers to both the number of pixels in an image and the total pixels on the camera sensor. To calculate megapixels, you multiply the sensor’s width by its height in pixels. For example, a sensor that produces images of 4288 × 2848 pixels has 12.2 megapixels (4288 × 2848 = 12,212,224).

Due to misleading marketing, many believe that a higher megapixel count automatically equates to better image quality. While a higher pixel count can theoretically provide higher resolution, affecting the maximum print size, image quality also relies on several other factors:

• Dynamic Range: The sensor’s ability to capture details in both highlights and shadows.
• ISO Sensitivity: The sensor’s sensitivity to light, defined by ISO (International Organization for Standardization). Advanced sensor technology can minimize noise at high ISO levels, improving image quality in low-light conditions.
• Sharpness: The overall clarity of an image, defined by focus and contrast. A sharp image appears clear and detailed, with high contrast and texture. An image lacking sharpness, often described as “soft,” can look blurry and lack detail

Dynamic range and ISO sensitivity are characteristics solely dependent on the sensor, influenced by its size and technology. Sharpness, on the other hand, is affected not only by the sensor but also by the quality of the lens used.

These concepts are complex, and I’ve aimed to simplify them in this article. I will dedicate separate articles to each of these topics later in this photography course.

Simply put, with the same technology and megapixel count, a larger sensor will offer greater dynamic range and produce less noise at high ISO settings compared to a smaller sensor. This is why having 18 megapixels on a 36×24mm (full-frame) sensor is vastly different from having the same megapixel count on a 6.16×4.62mm sensor.