In photography, focal length and effective focal length are terms often used interchangeably, yet they describe very different concepts that can drastically impact your images. Understanding the difference is key to getting the shots you want, whether you’re shooting landscapes, portraits, or action.
In short, focal length directly influences your field of view, compression, and the overall feel of your image, while effective focal length comes into play when using crop sensor cameras and adds another layer to how we frame our subjects.
In this article, we’ll dive into what focal length and effective focal length really mean, why the distinction matters, and how to choose the right setup for your style and equipment. If you’ve ever been puzzled by terms like “crop factor” or “full-frame equivalent,” you’re in the right place! Get ready to discover how understanding these details can help you make the most of your lenses and unlock new creative possibilities.
Table of Contents
- Introduction to Focal Length
- Understanding Effective Focal Length
- Crop Factor and Its Role
- How Focal Length Affects Depth of Field and Compression
- Why It Matters: Practical Implications of Focal Length in Photography
- Choosing Lenses with Your Camera’s Crop Factor in Mind
Introduction to Focal Length
As discussed in the video above by Apalapse, focal length is a measurement, in millimeters, that indicates the distance between the lens and the camera’s image sensor when the lens is focused on a subject at infinity. In simpler terms, focal length determines how “zoomed in” or “zoomed out” your image will appear and affects the composition in several key ways:
- Field of View: Focal length controls the area the camera can capture. A short focal length (e.g., 18mm) has a wide field of view, suitable for landscapes, while a long focal length (e.g., 200mm) has a narrow field of view, often ideal for portraits and wildlife.
- Subject Compression: A longer focal length compresses the background, making it appear closer to the subject, while a shorter focal length emphasizes distance.
- Creative Uses: Different focal lengths serve different creative needs. Wide-angle lenses (short focal lengths) capture vast landscapes, while telephoto lenses (long focal lengths) are ideal for isolating subjects and bringing them closer.
Understanding Effective Focal Length
Effective focal length, also known as the “equivalent focal length,” becomes relevant when using cameras with smaller-than-full-frame sensors. While the actual focal length of the lens remains unchanged, the effective focal length refers to how a lens behaves on crop sensors, which “crop” the image, giving the impression of a longer focal length.
For example:
- A 50mm lens on a full frame camera has a standard field of view.
- On an APS-C sensor (with a 1.5x crop factor), this same 50mm lens behaves more like a 75mm lens, narrowing the field of view.
Understanding effective focal length helps you anticipate how lenses will perform across different sensor types so you can choose the proper lens for the images you wish to create. This guide by Anton Gorlin goes into more detail about effective focal length and how to calculate it.
Crop Factor and Its Role
The Nikon Z30 shown above has a 1.5x crop factor. So, the 16-50mm lens that accompanies it behaves like a 24-75mm lens.
Crop factor is a multiplier based on the size of your camera’s sensor relative to a full-frame sensor. Here are some common crop factors:
- APS-C sensors: 1.5x or 1.6x crop factor
- Micro Four Thirds sensors: 2x crop factor
To calculate effective focal length, multiply the actual focal length by the crop factor. For example:
- A 35mm lens on a 1.5x APS-C sensor has an effective focal length of 52.5mm (35mm x 1.5).
This adjustment is essential when deciding on focal length because it helps predict the field of view. For instance, wildlife photographers using cameras with crop sensors can achieve tighter frames without using a longer lens because of the crop factor.
Keep Reading: Camera Basics for Beginners
How Focal Length Affects Depth of Field and Compression
Photo by David Liebst via Shutterstock
Focal length also influences depth of field (DOF) and compression. Here’s how each is affected:
- Depth of Field: The longer the focal length, the shallower the depth of field, creating more background blur, which can be excellent for isolating subjects. The image above, for example, was shot with an 85mm lens at f/1.2.
- Compression: Longer focal lengths also compress space, making background elements appear closer to the subject, while shorter focal lengths stretch distances, giving a sense of depth. The image below, for example, was shot with a 35mm lens.
Photo by Andrew Mayovskyy via Shutterstock
However, effective focal length only changes the field of view, not the actual focal length. For example, a 50mm lens on a crop sensor camera still has a 50mm focal length in terms of optics and depth of field, even if it captures a narrower view.
Why It Matters: Practical Implications of Focal Length in Photography
Photo by Mongkolchon Akesin via Shutterstock
Understanding focal length and effective focal length can shape the way you approach various photography styles. Here’s how this knowledge applies to different scenarios:
- Landscape Photography: Landscapes often benefit from wide angles (e.g., 16-24mm on full-frame) to capture vast scenes. For crop sensor users, a 10-18mm lens offers a similar wide-angle field of view.
- Portrait Photography: Traditional portrait focal lengths, like 85mm on full-frame, provide flattering compression. With a crop sensor, a 50mm lens offers a similar perspective, achieving effective focal lengths around 75mm on APS-C cameras.
- Wildlife Photography: Wildlife photographers often use long lenses (200mm+) to capture distant animals. On a crop sensor, a 200mm lens offers an effective focal length of around 300mm, helping to bring subjects closer without the weight and expense of a longer lens.
Choosing Lenses with Your Camera’s Crop Factor in Mind
Photo by Rawpixel.com via Shutterstock
If you’re shopping for lenses, consider your camera’s crop factor and the style of photography you enjoy. Here are some practical tips:
- For Full-Frame Users: What you see is what you get in terms of focal length, so a 24-70mm lens, for example, will offer the same field of view as expected.
- For Crop Sensor Users: Look for lenses designed specifically for crop sensors to achieve fields of view similar to full-frame setups. For instance, a 35mm lens on an APS-C sensor provides an effective focal length close to 50mm, ideal for general photography.
- Dual-System Users: If you use both crop and full-frame cameras, consider lenses that work well on both types of bodies. A 50mm lens can be a versatile choice, offering different fields of view depending on the camera.
Photo by Stivog via Shutterstock
In photography, understanding the difference between focal length and effective focal length is essential for making informed lens choices. Focal length shapes your image’s field of view and depth, while effective focal length offers an adjusted field of view when using crop sensor cameras.
Knowing how each works allows you to better visualize and plan your shots, whether you’re capturing a sweeping landscape, a portrait with a beautiful background blur, or a wildlife shot from afar. With this understanding, you’ll be able to use focal length to your advantage, unlocking new creative possibilities for every shot you take!
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Hero photo by Rawpixel.com via Shutterstock
