Tuesday, 21 August 2012

Understanding Digital Camera Sensors and Crop Factor

Crop factor is a word that is on the minds of all photographers who shoot digital. And it is one thing about which most of the beginners do not have a good idea about. So let us discuss the various sizes in which the modern day digital cameras sensors are available and how they affect different types of photography.

In the case of film cameras there was no such confusion as the standard 35mm film was used in all the cameras regardless of its make and model. Shown below is the standard 35mm film; it is 36mm by 24 mm in size and it is the size to which modern day digital camera sensors are compared.

Camera Film
Camera Film

Any digital camera with a sensor size equalling the 35mm film size is called a full frame sensor or a full frame DSLR camera. And cameras which have sensors of smaller dimensions are called crop sensor cameras.

Let us take a look at some of the most popular crop sizes and cameras employing them

Digital Camera Sensors
Photo By Viamoi

Crop Factor     Camera Models

1.3x                  Canon EOS 1D/1D MkIIN
1.5x                  Nikon D40/D50/D70/D70s/D80/D200/D2XD2Hs Minolta 7D/Fuji S3 Pro/ Pentax 
1.6x                  Canon EOS 350D/450D/20D/30D
2.0x                  Olympus E-400/E-500/E-300/E-1

Sensor sizes of 1.5x crop and 1.6 crops together are referred to as APS-C Sized Sensors.

Camera phones and other compact cameras mainly use 1/4" to 2/3" sensor sizes. One resent development is that of the 4/3 format with a crop factor of 2X jointly developed by Olympus, Fuji and Kodak.

So what are the differences in images between these various crop sizes and which one is best for me?

The main areas where sensor size makes a difference are depth of field, image noise, diffraction, size/weight and finally cost. Lets us discuss how sensor size affects these factors one by one.

Focal Length

The effective focal length of lenses is based on the standard 35mm film format or the full frame digital sensor. But when these are used with crop sensors the effective focal length becomes much larger. For example a 50mm prime lens on a full frame camera produces exactly 50mm field of view but when used with a crop sensor results in much longer effective focal lengths. Let’s take a look at some of the most popular crop sensors.

Lens Crop Factor
Lens Crop Factor – source - Wikipedia

Crop Factor     Effective Focal Length of a 50mm lens

1.3x                 63mm
1.5x                 76mm
1.6x                 80mm
4/3                  100mm

Sensor Size and its affect on Depth of Field

Larger sensor = Lesser Depth of Field and Smaller sensor = Greater Depth of Field

Depth of field decreases when the distance between the subject and the lens is reduced. At any given aperture a larger sensor camera need to be closer to the subject than a camera with a smaller sensor to get the same angle of view; and as a result reduced depth of field.

Sensor Size and Image Noise

Larger Sensor = Less Image Noise and Smaller sensor = More Image Noise

Low light high ISO performance is one area in which larger sensors excel. Due to their higher light gathering capacity and the presence more numbers of pixels, cameras with larger sensors are better equipped at high ISO levels than their counterparts with comparatively smaller sensors.

Sensor Size and Diffraction

Cameras employing larger sensors could use smaller aperture values than those with smaller sensors. We will be covering this topic in detail in later articles.

Size/Weight of Equipment

If your nature of work involves carrying the camera for extended periods of time and if size and weight is a major factor then do pay attention to these factors.

Cameras with larger sensors are normally bigger and bulkier than those with smaller sensors. Also as explained in the focal length section above crop sensor cameras have longer effective focal lengths for your zoom lenses, so if you are into wildlife photography or sports photography or any other genre of photography that relies mainly on the telephoto end of the lenses, you will be able to get maximum zoom with smaller sensor cameras. Meaning you could manage with smaller lenses and still get longer zoom range.

dslr sensor comparison
Size comparison of Crop Sensor camera with Full frame camera Source:- Wikipedia

The above picture shows a comparison between a crop sensor camera and a full frame camera.

OK and what if your genre of photography is either Landscape photography or Architecture Photography. Both involve use of ultra wide angle lenses.

Generally edge sharpness is one of the important criteria for lens quality and crop sensor cameras could get away with low quality lenses as they anyhow crop away the edges automatically. But when it comes to using ultra wide angle lenses, crop sensor cameras have limited flexibility. There are mainly two reasons, first is that a crop sensor camera should use comparatively wider lenses to get the same field of view as a full frame sensor. And unfortunately there are not much lens options in such wide range, moreover lens quality for wide angle lenses are not at par with their telephoto counterparts so the wider the lens being used the lesser the image quality.

It is also to be noted that some speciality lenses like tilt shift lenses and fast ultra wide angle lenses are not compatible with cameras with crop sensors.

Large sensors provide more control and greater artistic flexibility as they allow creating shallower depth of field than possible with a crop sensor. But they are comparatively bulkier, heavier and more expensive to own. So in conclusion it is the nature of work and the intended final print size that determines the choice of sensor size.