what is crop factor
(focal length multiplier)

Understand the terms crop factor and full size sensor will help you when you are considering options on buying or using different lens and camera combinations. This post will give you a deeper understanding on crop factor and you can get more information about full-sized sensors here.

crop factor comparison

Before the advent of digital cameras and digital sensors, camera and lens manufactures made their cameras to work with 35mm film. It was the most popular and most widely used format in photography for many years.

It was easy to compare different camera lenses, their focal lengths and their zoom ranges. A 50mm lens was considered "normal" and was normal on any other 35mm camera you used it on. Longer lens were considered telephoto and had a narrower, close-up view on any 35mm camera you used it on. Shorter lenses were considered to be wide-angle and show a wider, farther-back view of the scene, also on any 35mm camera. It was simple.

Now, enter some confusion. Digital cameras can be made with any size sensor, with or without a full size sensor, which is a sensor that is the same size as a 35mm film "negative." As it turns out, The most popular sensor size in digital cameras these days is an APS-C format

The illustration above show you what would happen if you used the same lens on cameras having smaller than full frame sensors. A "crop factor" means that your photograph would have a smaller field of view. In other words, it crops part of the photograph that the lens is capable of including in your photo. It's also referred to as a focal length multiplier.

As a result – when you fit a lens to a camera with a smaller sensor the lens is often said to have a larger equivalent lens size. Depending on how much smaller the sensor size is than full, the focal length multiplier  can be calculated.

how to calculate crop factor

The easiest way to calculate crop factor is to use this free online calculator. This simple tool has a drop down selector where you can type in the exact dimensions of your camera's sensor and it will automatically calculate the number for you. How cool is that?

Online crop factor calculator

Also very cool and even more valuable  is the lens equivalency calculator. Use the drop down menu to pick your camera's sensor size, fill in your lens focal length and maximum f/stop, and it will tell you the lens equivalent on a full frame sensor. Then you'll know if it's a wide angle, normal, or telephoto lens or what zoom range it covers.

crop factor chart

The chart below shows you how a certain lens "acts" when it's on a cropped sensor camera. What it really means is it shows the lens focal length that has the same angle of view as a full frame camera would give you.

lens conversion chartCrop Factor Chart

Look at the 2 highlighted spots in the chart above. Using a 50 mm lens on a camera with a full size sensor would give you the same effect of using an 80 mm lens when using that same lens on a camera with a 1.6 factor sensor.

That lens would be "normal" on a full size sensor camera and would be a telephoto lens on the camera with the smaller sensor. It is easy to erroneously think in our minds as photographers that putting a certain lens on a smaller crop sensor gives it extra zooming power.  One of the big considerations in choosing a camera based on sensor size that many can easily ignore is depth of field.

Depth of field in photography is greater with smaller sensor cameras.  In cell phone cameras for instance, the physical dimensions of the sensors are so small that they inherently have a very large range of things in focus compared to a full-sized sensor camera.

Camera buying advice.  A guide to help you chose the right camera. Don't get fooled by the megapixel myth. Stay inspired about photography. Shoot more and watch less TV.

Article published by Bruce Lovelace


Bruce is the publisher of Better Digital Photo Tips. Read more on the About Page. He's been known as The Traveling Photographer ever since he started his location photography business in 1994.

View some of Bruce's photos on Instagram.   Visit the Facebook Page. Watch him on YouTube.  Bruce runs photo workshops and provides one on one digital photography coaching.

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