Sony Cyber-shot DSC-T50 vs. Sony Alpha SLT-A55

Diagonal is calculated by the use of Pythagorean theorem:

Diagonal = √

w² + h²

where w = sensor width and h = sensor height

The diagonal of T50 sensor is not 1/2.5 or 0.4" (10.2 mm) as you might expect, but approximately two thirds of that value - 7.19 mm. If you want to know why, see sensor sizes.

w = 5.75 mm
h = 4.32 mm

Diagonal = √

5.75² + 4.32²

= 7.19 mm

w = 23.50 mm
h = 15.60 mm

Diagonal = √

23.50² + 15.60²

= 28.21 mm

Surface area is calculated by multiplying the width and the height of a sensor.

Width = 5.75 mm
Height = 4.32 mm

Surface area = 5.75 × 4.32 = 24.84 mm²

Width = 23.50 mm
Height = 15.60 mm

Surface area = 23.50 × 15.60 = 366.60 mm²

Pixel pitch is the distance from the center of one pixel to the center of the next measured in micrometers (µm). It can be calculated with the following formula:

Pixel pitch =	sensor width in mm	× 1000
	sensor resolution width in pixels

Sensor width = 5.75 mm
Sensor resolution width = 3095 pixels

Pixel pitch =	5.75	× 1000	= 1.86 µm
	3095

Sensor width = 23.50 mm
Sensor resolution width = 4945 pixels

Pixel pitch =	23.50	× 1000	= 4.75 µm
	4945

The area of one pixel can be calculated by simply squaring the pixel pitch:

You could also divide sensor surface area with effective megapixels:

Pixel area =	sensor surface area in mm²
	effective megapixels

Pixel pitch = 1.86 µm

Pixel area = 1.86² = 3.46 µm²

Pixel pitch = 4.75 µm

Pixel area = 4.75² = 22.56 µm²

Pixel density can be calculated with the following formula:

Pixel density =  (	sensor resolution width in pixels	)² / 1000000
	sensor width in cm

One could also use this formula:

Pixel density =	effective megapixels × 1000000	/ 10000
	sensor surface area in mm²

Sensor resolution width = 3095 pixels
Sensor width = 0.575 cm

Pixel density = (3095 / 0.575)² / 1000000 = 28.97 MP/cm²

Sensor resolution width = 4945 pixels
Sensor width = 2.35 cm

Pixel density = (4945 / 2.35)² / 1000000 = 4.43 MP/cm²

Sensor resolution is calculated from sensor size and effective megapixels. It's slightly higher than maximum (not interpolated) image resolution which is usually stated on camera specifications. Sensor resolution is used in pixel pitch, pixel area, and pixel density formula. For sake of simplicity, we're going to calculate it in 3 stages.

1. First we need to find the ratio between horizontal and vertical length by dividing the former with the latter (aspect ratio). It's usually 1.33 (4:3) or 1.5 (3:2), but not always.

2. With the ratio (r) known we can calculate the X from the formula below, where X is a vertical number of pixels:

(X × r) × X = effective megapixels × 1000000    →

X = √  effective megapixels × 1000000 r

3. To get sensor resolution we then multiply X with the corresponding ratio:

Resolution horizontal: X × r
Resolution vertical: X

Sensor width = 5.75 mm
Sensor height = 4.32 mm
Effective megapixels = 7.20

r = 5.75/4.32 = 1.33

X = √  7.20 × 1000000  = 2327 1.33

Resolution horizontal: X × r = 2327 × 1.33 = 3095
Resolution vertical: X = 2327

Sensor resolution = 3095 x 2327

Sensor width = 23.50 mm
Sensor height = 15.60 mm
Effective megapixels = 16.20

r = 23.50/15.60 = 1.51

X = √  16.20 × 1000000  = 3275 1.51

Resolution horizontal: X × r = 3275 × 1.51 = 4945
Resolution vertical: X = 3275

Sensor resolution = 4945 x 3275

Crop factor or focal length multiplier is calculated by dividing the diagonal of 35 mm film (43.27 mm) with the diagonal of the sensor.

Crop factor =	43.27 mm
	sensor diagonal in mm

Sensor diagonal in mm = 7.19 mm

Crop factor =	43.27	= 6.02
	7.19

Sensor diagonal in mm = 28.21 mm

Crop factor =	43.27	= 1.53
	28.21

Equivalent aperture (in 135 film terms) is calculated by multiplying lens aperture with crop factor (a.k.a. focal length multiplier).

Crop factor = 6.02
Aperture = f3.5 - f4.3

35-mm equivalent aperture = (f3.5 - f4.3) × 6.02 = f21.1 - f25.9

Aperture is a lens characteristic, so it's calculated only for fixed lens cameras. If you want to know the equivalent aperture for Sony Alpha SLT-A55, take the aperture of the lens you're using and multiply it with crop factor.

Crop factor for Sony Alpha SLT-A55 is 1.53