Crop Sensors vs. Full Frame Sensors: A Beginner's Guide

Let’s set the scene: for a while now, you’ve had that beginner’s photography kit that you purchased online or from a trusted friend. You’re ready to upgrade your equipment and really fall into the rabbit hole of purchasing lenses. You open up your browser and see an advertisement that reads “FULL FRAME EF-M MOUNT FRIENDLY PRIME 50MM 1.5/f FOR SALE TODAY!!”

What the heck do any of those words mean?!, you wonder. Well, after reading this guide, you’ll be able to read that gibberish AND understand it! Don’t worry, this guide is beginner-friendly (and won’t shame any intermediates who need a refresher either).

Camera Sensors

Using our example lens description (the full frame EF-M mount friendly 75MM 1.5/f), let’s talk about the main idea: camera sensors.

In ye olden film times, you would capture a scene by exposing a piece of film to light, burning the image into it. It needed a particular type of lens to do this film magic, so normally the lens would be built into the body of the camera.

Nowadays, we do this process digitally with the camera’s built-in sensor, and that’s why we can change the lenses of a camera. Thus, the name Digital Single-Lens Reflex (DSLR).

When it comes to DSLRs, there are two main types of sensors: Full Frame Sensors and Advanced Photo System type-C (or APS-C or more commonly referred to as “Crop Sensors”).

Full Frame Sensors vs. Crop Sensors

Full Frame Sensors are designed to capture images up to 36mm x 24mm. These sensors are the equivalent to the frames you would get from old school, physical film. These sensors capture more images and are usually more expensive.

APS-C (we’ll call these Crop Sensors from now on) are designed to capture images up to 22.3mm x 14.9 mm. This gives your camera’s sensor a smaller frame of view. That means it won’t capture as much of the image as a Full Frame Sensor could. Since you’re not working with as much space, Crop Sensors “zoom in” on whatever you’re capturing by a rate of 1.6x. This “zoom in” is referred to as a “crop factor.”

Take for example, the full frame EF-M mount friendly 75MM 1.5/f. Our lens says it is designed for a full frame sensor and is 50mm. So, a Full Frame Sensor camera will read the image at the full 50mm. That exact same lens will read as an 80mm lens when using a Crop Sensor camera.

Beginner’s Way to Think About This:

• A cropped sensor can only see so much of an image. It’s like trying to read a book only using a magnifying glass.
• A full frame sensor can see everything. It’s like looking at a page in the book.

The length (50mm for our example) of your lens isn’t what determines the sensor; that information is within your camera itself. The length of your lens will change how much of an image your camera will capture.

Intermediate’s Refresher:

• Cropped sensors add a 1.6x magnification to your overall image, but the quality is determined by your megapixel count.
• Full frame sensors will read the image at its full ratio but not quality. You won’t lose any quality, but you won’t gain anything either.

Camera Mounts

Now that we’ve got a basic understanding of how the sensor in your camera determines the amount of picture you can get, it’s time we talk about the different camera mounts. “Wait, there’s more to this conversation?!” Yes, yes there is.

Quick Terms to Know

• “EF” - Electro Focus. These are lenses that come with an “autofocus” feature
• Mount - type of lens that fits a specific type of camera
• Vignetting - black ring or haze around an image. This happens when a lens isn’t the right fit for the camera.
                                   
  EF Mount 
  An EF Mount is a lens designed for Full Frame Sensors. They’re usually more expensive, but honestly they’re worth it. They can be interchanged between EF and EF-S mounts without losing the image quality. Of course, when you use it on a Crop Sensor, you will still get the crop factor (but you knew that already).
                                   
  EF-S Mount
  An EF-S Mount lens is designed specifically for Crop Sensors. These types of lenses have a smaller diameter to accommodate the smaller frame of view for the sensor. Essentially, this equates to not having to worry about that 1.6x magnifying.
                                   
  They can technically sit on an EF Mount, but you will get extreme vignetting. However, these lenses are usually cheaper because of their smaller size.
                                   
  EF-M Mount
  The EF-M mount was introduced in 2012 by Canon as a way of compensating for their new, mirrorless camera bodies. These types of mounts have a smaller diameter but larger focal distance than their EF and EF-S predecessors. There are adaptors for EF-S to EF-M and EF to EF-M, but you don’t really gain any of the benefits of the EF-M, because the adaptor would block the extra space. Basically, it is another type of mount. The only real difference and suggestion when it comes to the EF-M mount lenses is: only use EF-M lenses on EF-M cameras.

Adaptors

Regardless of what type of mount your DSLR has, there are always adaptors that can help make any lens fit any camera. Just be aware that you may end up with vignetting or the corners of the image being distorted.

So, taking our original example, we know the following information:

• FULL FRAME - this lens works best on cameras that have a full frame sensor.
• EF-M MOUNT FRIENDLY - this lens will work best on cameras that have an EF-M mount, which we also know are full frame!
• PRIME- This tells you if you can zoom with the lens or not.
  •  Prime = no zooming
  • Zoom = yes zooming
•  50MM - this lens has a focal length of 50mm. Since it’s already designed for a camera that has a full frame sensor, we don’t have to worry about cropping.
• 1.5/f - this is your f-stop or aperture number. It tells you how much light your lens can give to your camera’s sensor. The lower the number, the more light you have coming in.
• FOR SALE TODAY!! - you will probably see this lens for sale again tomorrow.

TL;DR - The sensor is determined by your camera itself. If it’s a full frame camera, use full frame lenses or prepare to have a 1.6x zoom. If your camera has a crop sensor, you’ll always have less image.

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Note From Tongal: This blog is part of a series of Tongal Community-written blog posts that were originally sourced in the Tongal Blog Open Call Project. The views and opinions expressed in this article are those of the author(s) and do not necessarily reflect the official policy or position of Tongal. Read more Tongal Community-written posts here!