Full frame versus cropped sensor
What is a full frame camera? What is a cropped Sensor camera? and what is the crop factor?
If you own a digital camera, it is important to be familiar with the terms Full frame and Cropped sensors.
Full frame (sensor cameras)
A full-frame Camera is one with an image sensor format that is the same size as 35 mm film format. Dimension of a full frame is 36 mm X 24 mm, aspect ratio of 3:2 and a diagonal measurement of approximately 43 mm. The name “35 mm” refers to the total width of the 135 film, which was the primary medium of the format prior to the invention of digital cameras.
Crop(ped) or APS sensor
In 1996, a smaller film format called “Advanced Photo System (APS)” was introduced. There were three APS classes;
- APS-H; H for High Definition; dimensions: 30.2 x 16.7 mm
- APS-C; C for Classic; dimensions: 25.1 x 16.7 mm
- APS-P; P for Panoramic; dimensions; 30.2 x 9.5 mm
In digital cameras, APS sensors exist in many different variants depending on the manufacturer and camera model. But all APS or cropped sensors are smaller than full frame sensors. APS-C is a common image sensor format, which is approximately equivalent in size to the APS film negative in its C format, of 25.1×16.7 mm, with an aspect ratio of 3:2.
The sensor size have some important implications, which we will briefly discuss in the next few paragraphs.
Cropped sensor creates a smaller angle of view
Imagine you mount a 50 mm lens on a full frame camera that is set on a tripod in a distance from a tree so you would see the entire tree in your viewfinder (figure 1).
Figure 1: In this case, the sensor is large enough to capture the entire image of the tree.
In the next step we mount the same 50 mm lens on a cropped sensor camera, from the same distance to the tree. Hence the only change is a smaller sensor. Now the lens will affect the incoming light in exactly the same way as it did in the previous experiment and it will create the same image of the tree. But the problem is that the camera sensor is much smaller and as a result parts of the tree’s image will fall outside the edges of the image sensor (Figure 2). Exactly, as if you would have zoomed in on the tree or as if you would have cropped the image. In other words, with an APS sensor, your angle of view will become smaller in comparison to a full frame sensor.
Note: Angle of view refers to the image area that a camera can capture (vertically and horizontally), and it depends on the focal length of your lens and the sensor size. Smaller focal length creates larger angle of view. Larger sensor allows capturing a larger angle of view. Angle of coverage, however, refers to the image circle that is created by a lens at a given focal length. Normally the angle of coverage is large enough to cover the entire image sensor. If not, a dark circle will be visible.
Figure 2: In this case, nothing is changed but the size of the sensor (it is smaller). As a result some parts of the tree will fall outside the edges of the image sensor and will not appear in the final image.
The phenomenon you saw in figure 1 and 2 has some important practical implications. Consider you are shooting a real state project and your aim is to shoot with a 24 mm lens in order to have a wide angle of view. However, mounting a 24 mm lens on a camera with APS-C sensor will give you an angle of view almost equal to a 35 mm lens (,which is a much smaller angle of view) and may not work for you. In order to prevent such a situation you need to be familiar with another terminology, which is the “crop factor”.
Figure 3. Dividing the diagonal diameter of a full frame sensor (43.3 mm) by the diagonal diameter of your APS sensor will give you the crop factor of your camera sensor.
Crop factor -also known as focal length multiplier- is basically the ratio of the size of the full-frame sensor to the size of a smaller sensor; generally the diagonal dimension of a 35 mm sensor (43.3 mm) to the diagonal dimension of the APS sensor and it is typically in the range of 1.3 to 2. So, in case you have a crop-sensor camera you need to find out what the crop factor of your camera sensor is.
How can you use the crop factor to choose the right lens for the purpose of your shooting? Let’s say you are going for street photography and you wish to have the angle of view of a 50 mm lens on your APS-C camera, which has a crop factor of 1.5. If you divide 50 by 1.5 you will have a lens with a focal length close to 35 mm. Hence, a 35 mm lens on your APS-C camera will give you the same angle of view as a 50 mm lens would do on a full frame camera. Alternatively if you have a lens with a focal length of X (any possible focal length like 12, 24, 35, ….) and you want to know what would be its comparable focal length on a full frame, you multiply it by the crop factor of your camera. For instance a 50 mm lens on a APS-C camera with a crop factor of 1.6 will have the angle of view of a 80 mm lens on a full frame camera (50 mm x 1.6 = 80 mm).
This may sound negative that an APS sensor will give you a smaller angle of view. But don’t rush in your judgment. Although you will loose some part of the scene when working with a wide angle lens, you will gain much more reach when shooting with a telephoto lens! Imagine you have a 200 mm lens on your APS camera with a crop factor of 1.5, this will give you the same angle of view of a 300 mm lens on a full frame camera! (200mm X 1.5 = 300 mm). This is a pleasant gain when shooting e.g. wild life or sport.
Cropped sensor creates a deeper depth of field
In keeping with the same example presented in figure 1-2, imagine you would want to have the same angle of view with your cropped sensor camera as you would have with a full frame camera. What would you do? Apart from cutting the edges of the tree, you have two feasible photographic options; 1- you can step back in order to increase your distance from the subject or, 2- using a lens with a wider angle of view. Both solutions will result in a deeper depth of field, provided all other parameters remain the same.
With a cropped sensor possible edge vignetting decreases
Edge vignetting might be the result of optical impurities and could be visible as a dark edge around your image. Although this problem is easy to fix in post-processing, when the same lens is mounted on a cropped sensor camera, provided it fits, the problem is less visible. Because the edges are not visible in the final image.
Full frame cameras may produce higher quality images at higher ISO and High dynamic range situations
Larger sensor size might result in lesser image noise at high ISO. Because, for a given number of pixels, pixel density is lower on a full frame camera (e.g. 24 mega pixels spread over a full frame or an APS-C sensor). When pixels density is not very high, there might be less noise from adjacent pixels, which may result in less image noise. In addition larger sensor size may allow to have larger pixels. Larger pixels, can capture more light before becoming over saturated and as a result it can deal better with a high dynamic range scene.
Manufacturing of a full frame sensor is expensive
Last but not least manufacturing of a full frame sensor is far more expensive than an APS sensor. That is why cameras with smaller sensor are much more affordable. It is also obvious that smaller sensor allows manufacturing compacter cameras.
A cropped sensor camera is: more affordable, compact, for a similar angle of view depth of field is greater and may have less visible edge vignetting.
A full frame camera: have a wider angle of view at a given focal length and might produces better image quality at high ISO and high dynamic range.
I hope you enjoyed reading this article. If you have any remaining question please feel free to send me an email.
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