Full Frame Lens on APS-C vs APS-C Lens on Full Frame Explained

Do you want to know the difference between a full frame lens on APS-C vs APS-C lens on full frame? Do you want to know which lenses can mount on which cameras and whether various camera/lens combinations are compatible?

That’s what this article is all about.

Full Frame Lens on APS-C vs APS-C Lens on Full Frame Explained

I’m going to explain whether you can use a full frame lens on an APS-C body. I’m going to explain whether you can use an APS-C lens on a full-frame body.

And you’ll come away knowing all about your camera and lens compatibility.

Sound good?

Let’s get started.

What Happens When You Attach a Full Frame Lens on APS-C Cameras?

A full-frame lens is designed for full-frame cameras. But what happens if you take that full-frame lens…

…and mount it onto an APS-C camera body?

In truth, not much at all.

Focal Length

First, the focal length of the lens doesn’t change. You see, the focal length of the lens is a physical property – it’s already fixed from the moment the lens is created. Focal length is the distance from a point inside the lens to the camera sensor, and this isn’t changed by a smaller, APS-C sensor.

Depth of Field (DoF)

Second, the depth of field doesn’t change. The depth of field is determined by the aperture, the focal length, and the distance from the lens to the point of focus; none of these are altered by an APS-C sensor.

Image Quality

Third, the quality of the lens stays the same. The optics of the lens remain constant no matter what camera you mount it on.

However, there is one feature that changes with an APS-C sensor size:

Lens’s Field of View

You see, whenever you mount a lens onto a camera, the lens projects a circular image onto the camera sensor.

(This is known as the circle of projection.)

That circular image is always the same size, no matter the camera sensor. But the camera sensor doesn’t always use this entire projected image. A full-frame lens is designed to project an image that’s perfect in size for a full frame camera sensor.

But when a full-frame lens is mounted onto a crop-sensor camera, the smaller sensor essentially crops the image projected by the full-frame lens. And you end up with a narrower field of view–that is, you end up with a narrower portion of the scene captured by the sensor.

Make sense?

Placing a smaller sensor behind a lens doesn’t change its focal length. What changes, is the angle of view only.

Advantages of Using Full-Frame Lens on APS-C Camera

Now that you know how a full-frame lens works on an APS-C camera, you can see that there is one big advantage to using this combination:

The narrower field of view increases lens reach, so you’re able to photograph more distant subjects with ease. This increased field of view is often referred to as a crop factor, where a 100mm lens is cropped to a 150mm lens on an APS-C camera.

(Despite this method of referring to APS-C cameras, the focal length doesn’t actually change! Only the field of view is affected.)

This is important for wildlife and sports photographers because they often need to capture images of subjects far off in the distance. It increases their lens’s reach, even though the focal length doesn’t change.

It is a common practice to use full frame lenses on crop (APS-C) cameras among wildlife photographer to increase the reach.

Disadvantages of Using Full-Frame Lens on APS-C Camera

There are a few important disadvantages to using this combination.

For one, full frame lenses tend to be bigger and more expensive than their APS-C counterparts.

Plus, while the extra reach is useful for sports and wildlife photographers, it makes wide-angle landscape photography a lot harder, because it nixes the ultra-wide field of view. That’s one of the reasons why many landscape photographers prefer to shoot full-frame, especially if their style involves creating ultra-wide, sweeping landscape photos.

Because of a crop factor, It is more difficult to design ultra-wide APS-C lenses than ultra-wide full frame lenses.

What Happens When You Attach an APS-C Lens on a Full-Frame Camera?

In many ways, attaching an APS-C lens on a full frame camera is just like attaching a full-frame lens to an APS-C camera.

Focal Length

For instance, the lens focal length doesn’t change – because just like a full-frame lens, the APS-C lens’s focal length is fixed from the moment it’s produced. Focal length is an optical property of the lens, completely unaffected by the sensor size.

Depth of Field (DoF)

And the lens’s depth of field doesn’t change, either, because the focal length of the lens remains constant.

Image Quality

Even the quality of the lens doesn’t change; as I explained above, a lens’s image quality isn’t influenced by the sensor size.

There is one issue with mounting an APS-C lens on a full-frame camera, however:

Image Projection

The image that’s projected by the lens is designed for APS-C sensors, not full-frame sensors. So it’s smaller than required and doesn’t cover the entire full-frame sensor.

Now, if you’re using Sony or Nikon cameras and lenses, then you can still mount an APS-C lens onto a full-frame camera. But you’ll often see vignetting (i.e., darkening) around the edges of the frame, which can easily ruin an image–unless you crop it out.

If you mount an APS-C lens on a full-frame Nikon and Sony camera and you don’t see vignetting, this is probably because the camera automatically identified the lens as APS-C and switched into a crop mode that uses only part of the sensor. This is a viable way of taking photos, but you’re going to lose some resolution. After all, the camera is cropping out megapixels!

Canon EF-S Lenses Issue

Note that things get a bit trickier when it comes to native Canon lenses. If you mount a Canon APS-C lens (labeled as an EF-S lens) onto a Canon full-frame camera, the lens mount will ram into the mechanism inside the camera, which you want to avoid at all costs. This won’t be a problem with third-party lenses for Canon APS-C cameras, but native EF-S lenses simply should not be mounted on Canon full-frame cameras.

If you can live with lower resolution images, it is absolutely possible to use APS-C lenses on full frame cameras.

Advantages of Using an APS-C Lens on a Full-Frame Camera

Here’s the main advantage of mounting APS-C lenses on full-frame cameras:

You can take advantage of smaller, cheaper APS-C lenses offered by manufacturers. These are often high-quality, but they cost much less than their full-frame equivalents.

For instance, Nikon users often mount the (APS-C mount) 35mm f/1.8 lens on full-frame bodies. This lens offers excellent quality and a compact build for an impressively low price.

Disadvantages of Using an APS-C Lens on a Full-Frame Camera

When you use an APS-C lens with a full-frame camera, you’re only using part of the sensor. This, in turn, reduces the resolution of the final image. You’ll be forced to crop, or your camera will crop for you–so that a 24 megapixel sensor produces a 10 megapixel image.

Conclusion

Now that you’ve finished this article, you know all about using APS-C lenses on full-frame sensors, as well full-frame lenses on APS-C sensors.

And you know the pros and cons of each option.

Just remember:

You don’t need to be afraid of mounting full-frame lenses on APS-C cameras, nor do you need to be afraid of the reverse.

(Unless you’re using a Canon EF-S lens on a full-frame camera–which you should never do!)

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by Viktor Elizarov
I am a travel photographer and educator from Montreal, Canada, and a founder of PhotoTraces. I travel around the world and share my experiences here. Feel free to check my Travel Portfolio and download Free Lightroom Presets.

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