The Textbook of Digital Photography - PhotoCourse

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image sensors—sizes and Aspect ratios...

The image sensor in a camera has two important and related physical charac-

teristics—its size and aspect ratio.

SenSor Size

Image sensors come in a variety of sizes with the smallest ones used in point

and shoot cameras and the largest in professional SLRs. Consumer SLRs of-

ten use sensors having the same size as a frame of APS film. Professional SLR

cameras occasionally use sensors the same size as a frame of 35mm film—

called full-frame sensors. (Large format cameras use even larger sensors.)

Larger image sensors generally have larger photosites that capture more light

with less noise. The result is pictures that are clearer, brighter, and sharper.

Because the size of photosites is so important, a large 6 Megapixel sensor will

often take better pictures than a smaller 8 Megapixel sensor. Not only is noise

a problem but smaller sensors also require better, more expensive lenses,

especially for wide-angle coverage. Here are some typical sensor sizes:

Size Width (mm) Height (mm) Used in

1/4 3.2 2.4 point & Shoot Cameras

1/3 4.8 3.6 point & Shoot Cameras

1/2 8 6.4 point & Shoot Cameras

2/3 11 8.8 point & Shoot Cameras

1 16 12.8 point & Shoot Cameras

apS-C 22.2 14.8 Consumer SLrs

Full frame 36 24 professional SLrs

Calculating Aspect ratios

Image sensors come in a variety of aspect ratios—the ratio of the sensor’s

width to height. The ratio of a square is 1:1 (equal width and height) and that

of 35mm film is 1.5:1 (1½ times wider than it is high). Most image sensors fall

in between these extremes. The aspect ratio of a sensor is important because

it determines the shape and proportions of the photographs you create. When

an image has a different aspect ratio that the device it’s displayed or printed

on, it has to be cropped or resized to fit. Your choice is to crop part of the

image or waste part of the paper or display area. To imagine this better, try

printing a square image on a rectangular sheet of paper so either the entire

image is printed or the entire paper is filled.

Image Width x Height Aspect Ratio

35mm film 36 x 24 1.50

Computer display 1024 x 768 1.33

Canon 5D 4368 x 2912 1.50

Canon s 3 is 2816 x 2112 1.33

Photo paper 4 x 6 1.50

Printing paper 8.5 x 11 1.29

HDTV 16 x 9 1.80

To calculate the aspect ratio of any camera, divide the largest number in its

resolution by the smallest number. For example, if a sensor has a resolution

of 4368 x 2912, divide the former by the later. In this case the aspect ratio is

1.5, the same as 35 mm film but different from an 8.5 x 11 sheet of paper.

image sensor sizes

range from the tiny

up to ones as large

as a frame of 35mm

film—called a full frame

sensor.

Click to explore the

sizes of image sensors.

The Effects of Compression

an image sensor

determines the shape of

your prints.

TiP

a 16:9 wide-screen

mode captures im-

ages and film clips

that are perfect for

display on your wide-

screen tV or com-

puter monitor.

Click here for a PDF

extension on pixels and

read Part 1 on aspect

ratios.

imAge sensors—size And AspeCt rAtios