Camera sensor size is a key aspect of photography because it affects image quality. Between two cameras with the same pixel count, the one with the physically larger sensor will typically produce better quality images.

This is due to the fact that photo receptors, which we now call pixels, are bigger on the larger sensor.

The primary purpose of a photo receptor is to collect light and produce an electrical signal that is then converted into a digital image signal, and the more light that is received by the sensor, the stronger the image signal will be.

Strong signals do not need as much amplification, and this means there is less occasion for image noise to be introduced or enhanced.

The most expensive component of a camera is typically its sensor, and this means that cameras with larger sensors tend to be considerably more expensive than cameras with smaller sensors.

The body of the camera also generally needs to be made bigger to house the larger sensor and to accommodate the lenses that are necessary to generate the larger image circle.

To summarise in general terms, cameras with bigger sensors tend to be larger and more expensive than those with smaller sensors, and they produce better quality images.

Bigger camera sensor or fewer pixels?

As mentioned earlier, bigger sensors allow the pixels to be made bigger and this has a positive influence on image quality, with a reduction of noise levels and an extension of dynamic range. Similar results can be achieved by keeping the pixel count down with a smaller camera sensor size.

Higher pixel counts, however, are frequently seen as a positive thing because images are larger and it allows for more detail to be recorded.

The challenge for manufacturers is to reduce noise levels and preserve image quality at the higher sensitivity settings when light levels are low.

Some cameras like the Nikon D4S offer advanced low light performance by having a reasonably low pixel count (16 million in the case of the D4S) and a large (full-frame) sensor.

This makes them quite versatile, but the images are not particularly large, and those wanting to produce big images with a lot of detail should select a high pixel count camera such as the Nikon D810, which has 36 million pixels on its full-frame sensor.

This camera has the ability to resolve a huge amount of detail, but it’s not the best choice for shooting in very low light. It will be interesting to see how the 50-million-pixel Canon EOS 5DS performs when it goes on sale in June this year.

What size is your sensor?

Full-frame cameras are called such because a full frame camera sensor size is the equivalent to a frame of 35mm film (26x24mm). APS-C format cameras are called such because their sensor is about the same size as the Classic format on the smaller APS-C format film.

These sensors generally measure 23.6×15.7mm in Nikon, Pentax, and Sony cameras or 22.2×14.8mm in Canon cameras. The Micro Four Thirds format uses a smaller camera sensor size which measures 17.3x13mm.

The size of the sensor inside many compact cameras and some compact system cameras is frequently given in imperial measurements that are based upon a system that was used for old television cameras. These measurements use fractions, which confuses things a bit and manufacturers can be rather cagey about giving actual dimensions.

However, a 2/3-inch sensor measures around 8.6×6.6mm and is larger than a 1/1.7-inch (7.6×5.7mm) and a 1/2/3-inch (1/0.6667-inch or 5.76×4.29mm) sensor.

While full-frame and APS-C format sensors are typically found in SLRs and compact system cameras, there are some compact cameras that have these larger sensors.

These are first-rate compact cameras that are designed to stand-in for an SLR. There are also large compact or bridge cameras that have relatively small sensors and some small compact system cameras (like the Pentax Q-series) that employ sensors that are more frequently found in compact cameras.

It is worth your time to check the sensor size of a camera in addition to its pixel count when you are considering a purchase.

Focal length magnification

If a lens that is intended for a full-frame camera is mounted on a model with an APS-C format sensor, the image circle is much bigger than is required to cover the smaller sensor.

Consequently, the image will look like a cropped version of the one captured with the full-frame camera, or like the lens has been zoomed in to a longer focal length. Because of this, smaller sensors are frequently referred to as having a ‘crop’ or ‘focal length magnification’ factor.

This is intended to describe how images will look relative to those shot on full-frame cameras. Canon APS-C format SLRs have a 1.6x magnification factor while Nikon models have 1.5x magnification.

This means that on APS-C format a 100mm lens will produce images that resemble those captured at 160mm on a full-frame Canon camera, while the effective focal length of the same length lens on a Nikon APS-C format camera would be 150mm.

Usually, compact camera lenses are usually marked with their actual focal length, which due to the very small camera sensor size are often just a few millimetres.

They are, however, more frequently discussed in terms of their effective focal length. The Canon Ixus 27 HS, for example, has a 1/2/3-inch sensor and a lens with a focal length of 4.5-54mm.

However, this optic is typically called a 25-300mm lens because that is its equivalent focal length on a full-frame camera.

Other camera sensor sizes

While full-frame bodies are esteemed for their larger than average camera sensor size, in the hay day of film 35mm cameras were in fact known as ‘small format’ models.

Medium format cameras that took 120 film and produced negatives that measures 6x7cm, 6x6cm, or 6×4.5cm were a common choice for professional photographers and devoted enthusiasts.

However, those who wanted the best in image quality chose large format cameras that took sheets of film and produced images that measures 10×8 inches or 5×4 inches.

While there are digital medium format cameras available these days, their high price tag puts them securely in the sphere of professional photographers.

Their sensors, however, are actually much smaller than medium format negatives and regardless of its name, even the Pentax 645Z possesses a sensor that actually measures 44x33mm rather than the 60x45mm negatives of its film-based namesake.