Pentax K-r vs. Canon EOS Rebel T3i

Comparison

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K-r image
vs
EOS Rebel T3i image
Pentax K-r Canon EOS Rebel T3i
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Megapixels
12.40
18.00
Max. image resolution
4288 x 2848
5184 x 3456

Sensor

Sensor type
CMOS
CMOS
Sensor size
23.6 x 15.8 mm
22.3 x 14.9 mm
Sensor resolution
4299 x 2885
5196 x 3464
Diagonal
28.40 mm
26.82 mm
Sensor size comparison
Sensor size is generally a good indicator of the quality of the camera. Sensors can vary greatly in size. As a general rule, the bigger the sensor, the better the image quality.

Bigger sensors are more effective because they have more surface area to capture light. An important factor when comparing digital cameras is also camera generation. Generally, newer sensors will outperform the older.

Learn more about sensor sizes »

Actual sensor size

Note: Actual size is set to screen → change »
vs
1.12 : 1
(ratio)
Pentax K-r Canon EOS Rebel T3i
Surface area:
372.88 mm² vs 332.27 mm²
Difference: 40.61 mm² (12%)
K-r sensor is approx. 1.12x bigger than Rebel T3i sensor.
Pixel pitch
5.49 µm
4.29 µm
Pixel pitch tells you the distance from the center of one pixel (photosite) to the center of the next. It tells you how close the pixels are to each other.

The bigger the pixel pitch, the further apart they are and the bigger each pixel is. Bigger pixels tend to have better signal to noise ratio and greater dynamic range.
Difference: 1.2 µm (28%)
Pixel pitch of K-r is approx. 28% higher than pixel pitch of Rebel T3i.
Pixel area
30.14 µm²
18.4 µm²
Pixel or photosite area affects how much light per pixel can be gathered. The larger it is the more light can be collected by a single pixel.

Larger pixels have the potential to collect more photons, resulting in greater dynamic range, while smaller pixels provide higher resolutions (more detail) for a given sensor size.
Relative pixel sizes:
vs
Pixel area difference: 11.74 µm² (64%)
A pixel on Pentax K-r sensor is approx. 64% bigger than a pixel on Canon Rebel T3i.
Pixel density
3.32 MP/cm²
5.43 MP/cm²
Pixel density tells you how many million pixels fit or would fit in one square cm of the sensor.

Higher pixel density means smaller pixels and lower pixel density means larger pixels.
Difference: 2.11 µm (64%)
Canon Rebel T3i has approx. 64% higher pixel density than Pentax K-r.
To learn about the accuracy of these numbers, click here.



Specs

Pentax K-r
Canon Rebel T3i
Crop factor
1.52
1.61
Total megapixels
12.90
18.70
Effective megapixels
12.40
18.00
Optical zoom
Digital zoom
No
Yes
ISO sensitivity
Auto, 200 - 12800
Auto, 100, 200, 400, 800, 1600, 3200, 6400, (12800 with boost)
RAW
Manual focus
Normal focus range
Macro focus range
Focal length (35mm equiv.)
Aperture priority
Yes
Yes
Max. aperture
Max. aperture (35mm equiv.)
n/a
n/a
Metering
Centre weighted, Multi-segment, Spot
Multi, Center-weighted, Spot, Partial
Exposure compensation
±3 EV (in 1/3 EV, 1/2 EV steps)
±5 EV (in 1/3 EV, 1/2 EV steps)
Shutter priority
Yes
Yes
Min. shutter speed
30 sec
30 sec
Max. shutter speed
1/6000 sec
1/4000 sec
Built-in flash
External flash
Viewfinder
Optical (pentamirror)
Optical
White balance presets
10
6
Screen size
3"
3"
Screen resolution
920,000 dots
1,040,000 dots
Video capture
Max. video resolution
1920x1080 (30p/25p/24p)
Storage types
SDHC, Secure Digital
SDHC, SDXC, Secure Digital
USB
USB 2.0 (480 Mbit/sec)
USB 2.0 (480 Mbit/sec)
HDMI
Wireless
GPS
Battery
Lithium-Ion D-LI109 rechargeable battery
Li-Ion
Weight
598 g
570 g
Dimensions
125 x 97 x 68 mm
133.1 x 99.5 x 79.7 mm
Year
2010
2011




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vs

Diagonal

Diagonal is calculated by the use of Pythagorean theorem:
Diagonal =  w² + h²
where w = sensor width and h = sensor height

Pentax K-r diagonal

w = 23.60 mm
h = 15.80 mm
Diagonal =  23.60² + 15.80²   = 28.40 mm

Canon Rebel T3i diagonal

w = 22.30 mm
h = 14.90 mm
Diagonal =  22.30² + 14.90²   = 26.82 mm


Surface area

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

K-r sensor area

Width = 23.60 mm
Height = 15.80 mm

Surface area = 23.60 × 15.80 = 372.88 mm²

Rebel T3i sensor area

Width = 22.30 mm
Height = 14.90 mm

Surface area = 22.30 × 14.90 = 332.27 mm²


Pixel pitch

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

K-r pixel pitch

Sensor width = 23.60 mm
Sensor resolution width = 4299 pixels
Pixel pitch =   23.60  × 1000  = 5.49 µm
4299

Rebel T3i pixel pitch

Sensor width = 22.30 mm
Sensor resolution width = 5196 pixels
Pixel pitch =   22.30  × 1000  = 4.29 µm
5196


Pixel area

The area of one pixel can be calculated by simply squaring the pixel pitch:
Pixel area = pixel pitch²

You could also divide sensor surface area with effective megapixels:
Pixel area =   sensor surface area in mm²
effective megapixels

K-r pixel area

Pixel pitch = 5.49 µm

Pixel area = 5.49² = 30.14 µm²

Rebel T3i pixel area

Pixel pitch = 4.29 µm

Pixel area = 4.29² = 18.4 µm²


Pixel density

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

K-r pixel density

Sensor resolution width = 4299 pixels
Sensor width = 2.36 cm

Pixel density = (4299 / 2.36)² / 1000000 = 3.32 MP/cm²

Rebel T3i pixel density

Sensor resolution width = 5196 pixels
Sensor width = 2.23 cm

Pixel density = (5196 / 2.23)² / 1000000 = 5.43 MP/cm²


Sensor resolution

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

K-r sensor resolution

Sensor width = 23.60 mm
Sensor height = 15.80 mm
Effective megapixels = 12.40
r = 23.60/15.80 = 1.49
X =  12.40 × 1000000  = 2885
1.49
Resolution horizontal: X × r = 2885 × 1.49 = 4299
Resolution vertical: X = 2885

Sensor resolution = 4299 x 2885

Rebel T3i sensor resolution

Sensor width = 22.30 mm
Sensor height = 14.90 mm
Effective megapixels = 18.00
r = 22.30/14.90 = 1.5
X =  18.00 × 1000000  = 3464
1.5
Resolution horizontal: X × r = 3464 × 1.5 = 5196
Resolution vertical: X = 3464

Sensor resolution = 5196 x 3464


Crop factor

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


K-r crop factor

Sensor diagonal in mm = 28.40 mm
Crop factor =   43.27  = 1.52
28.40

Rebel T3i crop factor

Sensor diagonal in mm = 26.82 mm
Crop factor =   43.27  = 1.61
26.82

35 mm equivalent aperture

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

K-r equivalent aperture

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

Crop factor for Pentax K-r is 1.52

Rebel T3i equivalent aperture

Aperture is a lens characteristic, so it's calculated only for fixed lens cameras. If you want to know the equivalent aperture for Canon Rebel T3i, take the aperture of the lens you're using and multiply it with crop factor.

Crop factor for Canon Rebel T3i is 1.61

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