Pentax K-3 Mark III vs. Sony Alpha A7 III
Comparison
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| Pentax K-3 Mark III | Sony Alpha A7 III | ||||
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Megapixels
25.73
24.20
Max. image resolution
6192 x 4128
6000 x 4000
Sensor
Sensor type
CMOS
CMOS
Sensor size
23.3 x 15.5 mm
35.6 x 23.8 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 »
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 »
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| Pentax K-3 Mark III | Sony Alpha A7 III | |
Surface area:
| 361.15 mm² | vs | 847.28 mm² |
Difference: 486.13 mm² (135%)
Alpha A7 III sensor is approx. 2.35x bigger than K-3 Mark III sensor.
Note: You are comparing cameras of different generations.
There is a 3 year gap between Pentax K-3 Mark III (2021) and Sony Alpha A7 III (2018).
All things being equal, newer sensor generations generally outperform the older.
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.
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.
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.
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: 20.87 µm² (148%)
A pixel on Sony Alpha A7 III sensor is approx. 148% bigger than a pixel on Pentax K-3 Mark III.
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.
Higher pixel density means smaller pixels and lower pixel density means larger pixels.
To learn about the accuracy of these numbers,
click here.
Specs
Pentax K-3 Mark III
Sony Alpha A7 III
Total megapixels
26.78
25.30
Effective megapixels
25.73
24.20
Optical zoom
Digital zoom
Yes
Yes
ISO sensitivity
Auto (100-1600000)
100-25600 (expandable to 50 - 204800)
RAW
Manual focus
Normal focus range
Macro focus range
Focal length (35mm equiv.)
Aperture priority
Yes
Yes
Max. aperture
Metering
Multi, Center-weighted, Highlight-weighted, Spot
Multi, Center-weighted, Highlight-weighted, Spot
Exposure compensation
±5 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
1/8000 sec
1/8000 sec
Built-in flash
External flash
Viewfinder
Optical (pentaprism)
Electronic
White balance presets
8
10
Screen size
3.2"
3"
Screen resolution
1,620,000 dots
921,600 dots
Video capture
Max. video resolution
3840x2160 (30p/24p)
3840x2160 (30p/25p/24p)
Storage types
SD/SDHC/SDXC
SD/SDHC/SDXC, MS Duo/Pro Duo/Pro-HG Duo
USB
USB 3.0 (5 GBit/sec)
USB 3.0 (5 GBit/sec)
HDMI
Wireless
GPS
Battery
D-LI90 Lithium-ion battery
NP-FZ100 lithium-ion battery
Weight
820 g
650 g
Dimensions
134.5 x 103.5 x 73.5 mm
126.9 x 95.6 x 73.7 mm
Year
2021
2018
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Diagonal
Diagonal is calculated by the use of Pythagorean theorem:
where w = sensor width and h = sensor height
| Diagonal = √ | w² + h² |
Pentax K-3 Mark III diagonal
w = 23.30 mm
h = 15.50 mm
h = 15.50 mm
| Diagonal = √ | 23.30² + 15.50² | = 27.98 mm |
Sony Alpha A7 III diagonal
w = 35.60 mm
h = 23.80 mm
h = 23.80 mm
| Diagonal = √ | 35.60² + 23.80² | = 42.82 mm |
Surface area
Surface area is calculated by multiplying the width and the height of a sensor.
K-3 Mark III sensor area
Width = 23.30 mm
Height = 15.50 mm
Surface area = 23.30 × 15.50 = 361.15 mm²
Height = 15.50 mm
Surface area = 23.30 × 15.50 = 361.15 mm²
Alpha A7 III sensor area
Width = 35.60 mm
Height = 23.80 mm
Surface area = 35.60 × 23.80 = 847.28 mm²
Height = 23.80 mm
Surface area = 35.60 × 23.80 = 847.28 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-3 Mark III pixel pitch
Sensor width = 23.30 mm
Sensor resolution width = 6213 pixels
Sensor resolution width = 6213 pixels
| Pixel pitch = | 23.30 | × 1000 | = 3.75 µm |
| 6213 |
Alpha A7 III pixel pitch
Sensor width = 35.60 mm
Sensor resolution width = 6026 pixels
Sensor resolution width = 6026 pixels
| Pixel pitch = | 35.60 | × 1000 | = 5.91 µm |
| 6026 |
Pixel area
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 = pixel pitch²
You could also divide sensor surface area with effective megapixels:
| Pixel area = | sensor surface area in mm² |
| effective megapixels |
K-3 Mark III pixel area
Pixel pitch = 3.75 µm
Pixel area = 3.75² = 14.06 µm²
Pixel area = 3.75² = 14.06 µm²
Alpha A7 III pixel area
Pixel pitch = 5.91 µm
Pixel area = 5.91² = 34.93 µm²
Pixel area = 5.91² = 34.93 µm²
Pixel density
Pixel density can be calculated with the following formula:
One could also use this 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-3 Mark III pixel density
Sensor resolution width = 6213 pixels
Sensor width = 2.33 cm
Pixel density = (6213 / 2.33)² / 1000000 = 7.11 MP/cm²
Sensor width = 2.33 cm
Pixel density = (6213 / 2.33)² / 1000000 = 7.11 MP/cm²
Alpha A7 III pixel density
Sensor resolution width = 6026 pixels
Sensor width = 3.56 cm
Pixel density = (6026 / 3.56)² / 1000000 = 2.87 MP/cm²
Sensor width = 3.56 cm
Pixel density = (6026 / 3.56)² / 1000000 = 2.87 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:
3. To get sensor resolution we then multiply X with the corresponding ratio:
Resolution horizontal: X × r
Resolution vertical: X
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 → |
|
Resolution horizontal: X × r
Resolution vertical: X
K-3 Mark III sensor resolution
Sensor width = 23.30 mm
Sensor height = 15.50 mm
Effective megapixels = 25.73
Resolution horizontal: X × r = 4142 × 1.5 = 6213
Resolution vertical: X = 4142
Sensor resolution = 6213 x 4142
Sensor height = 15.50 mm
Effective megapixels = 25.73
| r = 23.30/15.50 = 1.5 |
|
Resolution vertical: X = 4142
Sensor resolution = 6213 x 4142
Alpha A7 III sensor resolution
Sensor width = 35.60 mm
Sensor height = 23.80 mm
Effective megapixels = 24.20
Resolution horizontal: X × r = 4017 × 1.5 = 6026
Resolution vertical: X = 4017
Sensor resolution = 6026 x 4017
Sensor height = 23.80 mm
Effective megapixels = 24.20
| r = 35.60/23.80 = 1.5 |
|
Resolution vertical: X = 4017
Sensor resolution = 6026 x 4017
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-3 Mark III crop factor
Sensor diagonal in mm = 27.98 mm
| Crop factor = | 43.27 | = 1.55 |
| 27.98 |
Alpha A7 III crop factor
Sensor diagonal in mm = 42.82 mm
| Crop factor = | 43.27 | = 1.01 |
| 42.82 |
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-3 Mark III 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-3 Mark III, take the aperture of the lens
you're using and multiply it with crop factor.
Crop factor for Pentax K-3 Mark III is 1.55
Crop factor for Pentax K-3 Mark III is 1.55
Alpha A7 III 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
Sony Alpha A7 III, take the aperture of the lens
you're using and multiply it with crop factor.
Crop factor for Sony Alpha A7 III is 1.01
Crop factor for Sony Alpha A7 III is 1.01
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