Understanding and Converting APS-C to Full-Frame Equivalents in Photography

Photography involves a lot of technicalities, and one of the key concepts that photographers often grapple with is the conversion from APS-C (also known as cropped film) to full-frame (FF) measurements. This article will guide you through the process of calculating the full-frame equivalent focal length, aperture, and field of view for APS-C lenses. Additionally, we will explore the limitations and alternatives for converting APS-C sensor cameras to full-frame systems.

Focal Length Conversion

To convert an APS-C focal length to its full-frame equivalent, you need to apply a crop factor, which is typically 1.5x for most APS-C sensors, though some Canon sensors have a crop factor of 1.6x. Here's a step-by-step guide:

Step 1: Determine the APS-C Focal Length

Identify the focal length of your APS-C lens.

Step 2: Apply the Crop Factor

Multiply the APS-C focal length by the crop factor to obtain the full-frame equivalent focal length. For example, if you have a 50mm APS-C lens, the full-frame equivalent focal length would be:

Full-Frame Equivalent Focal Length APS-C Focal Length x Crop Factor

50mm x 1.5 75mm

Depth of Field and Aperture Conversion

While the same aperture setting might behave differently between APS-C and full-frame sensors, you can approximate the full-frame equivalent aperture to achieve a similar depth of field (DoF). The formula for this conversion is:

Full-Frame Equivalent Aperture APS-C Aperture / Crop Factor

For instance, if you're using an f/2.8 lens on an APS-C camera, the full-frame equivalent aperture would be:

f/2.8 / 1.5 ≈ f/1.9

Field of View

The field of view on APS-C sensors is inherently narrower, meaning that an APS-C camera captures a more focused, tight frame compared to a full-frame camera with the same lens. Understanding this difference is crucial for composing your shots effectively.

Converting APS-C to Full-Frame

Photographers often wonder if they can convert their APS-C camera to a full-frame system. Sadly, the answer is no. Camera sensors are not physically upgradable, and the camera body is designed around either an APS-C or full-frame sensor. However, there are some alternatives:

Selling the APS-C Body: Consider selling your current APS-C camera body and using it as a backup, while upgrading to a full-frame body. This is often the most straightforward and cost-effective option. Using Full-Frame Lenses with a Focal Reducer: A focal reducer can be used with an APS-C mirrorless camera to simulate a full-frame sensor. These are often more affordable than a full-frame body, but they are not without limitations. A typical focal reducer can reduce the focal length of a lens by a factor of around 0.72, effectively making the lens about 1 stop brighter. The APS-C sensor still limits the view to about 1.5x narrower, but a focal reducer brings this to around 1.1x. The downside is that good focal reducers can be quite expensive. Using APS-C Lenses on Full-Frame Cameras: While APS-C lenses don't project a full-quality image on a larger full-frame sensor, you can take advantage of the full frame's resolution with two main methods:

Crop to APS-C Portion

Most full-frame cameras offer the option to crop the image to the APS-C portion of the sensor. This method is free but doesn't use the full resolution of the sensor.

Using a 1.5X Teleconverter

A 1.5X teleconverter can enlarge the image to cover the larger full-frame sensor, but it typically costs 1 stop of brightness. This method is more effective, but APS-C lenses are not compatible with all teleconverters. High-quality APS-C lenses in mounts like Sony A, Canon EF, and Nikon F can work well with a teleconverter, providing better image quality.

The main advantage of using a teleconverter is that it allows you to utilize the full resolution of the full-frame sensor, providing slightly better image quality than simply cropping the image.

Converting an APS-C camera to a full-frame system is not possible, but with the right tools and techniques, you can still take full advantage of a full-frame body while maintaining the functionality of your existing lenses.