Sony Alpha a9 vs. Nikon D850

Comparison

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Alpha a9 image
vs
D850 image
Sony Alpha a9 Nikon D850
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Megapixels
24.20
45.70
Max. image resolution
6000 x 4000
8256 x 5504

Sensor

Sensor type
CMOS
CMOS
Sensor size
35.6 x 23.8 mm
35.9 x 23.9 mm
Sensor resolution
6026 x 4017
8280 x 5520
Diagonal
42.82 mm
43.13 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 : 1.01
(ratio)
Sony Alpha a9 Nikon D850
Surface area:
847.28 mm² vs 858.01 mm²
Difference: 10.73 mm² (1%)
D850 sensor is slightly bigger than Alpha a9 sensor (only 1% difference).
Pixel pitch
5.91 µm
4.34 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: 1.57 µm (36%)
Pixel pitch of Alpha a9 is approx. 36% higher than pixel pitch of D850.
Pixel area
34.93 µm²
18.84 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: 16.09 µm² (85%)
A pixel on Sony Alpha a9 sensor is approx. 85% bigger than a pixel on Nikon D850.
Pixel density
2.87 MP/cm²
5.32 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: 2.45 µm (85%)
Nikon D850 has approx. 85% higher pixel density than Sony Alpha a9.
To learn about the accuracy of these numbers, click here.



Specs

Sony Alpha a9
Nikon D850
Crop factor
1.01
1
Total megapixels
28.30
46.89
Effective megapixels
24.20
45.70
Optical zoom
 
 
Digital zoom
Yes
Yes
ISO sensitivity
Auto, 100-51200 (expandable to 50-204800)
Auto, 64-25600 (extends to 32-102400)
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
Multi, Center-weighted, Highlight-weighted, Spot, Average
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, 1 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
Electronic
Optical (pentaprism)
White balance presets
10
14
Screen size
3"
3.2"
Screen resolution
1,440,000 dots
2,359,000 dots
Video capture
Max. video resolution
3840x2160 (30p/25p/24p)
3840x2160 (30p/25p/24p)
Storage types
SD/SDHC/SDXC/MS PRO Duo
SD/SDHC/SDXC/XQD
USB
USB 2.0 (480 Mbit/sec)
USB 3.0 (5 GBit/sec)
HDMI
Wireless
GPS
Battery
NP-FZ100 lithium-ion battery
EN-EL15a lithium-ion battery
Weight
673 g
915 g
Dimensions
126.9 x 95.6 x 63 mm
146 x 124 x 78.5 mm
Year
2017
2017




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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

Sony Alpha a9 diagonal

w = 35.60 mm
h = 23.80 mm
Diagonal =  35.60² + 23.80²   = 42.82 mm

Nikon D850 diagonal

w = 35.90 mm
h = 23.90 mm
Diagonal =  35.90² + 23.90²   = 43.13 mm


Surface area

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

Alpha a9 sensor area

Width = 35.60 mm
Height = 23.80 mm

Surface area = 35.60 × 23.80 = 847.28 mm²

D850 sensor area

Width = 35.90 mm
Height = 23.90 mm

Surface area = 35.90 × 23.90 = 858.01 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

Alpha a9 pixel pitch

Sensor width = 35.60 mm
Sensor resolution width = 6026 pixels
Pixel pitch =   35.60  × 1000  = 5.91 µm
6026

D850 pixel pitch

Sensor width = 35.90 mm
Sensor resolution width = 8280 pixels
Pixel pitch =   35.90  × 1000  = 4.34 µm
8280


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

Alpha a9 pixel area

Pixel pitch = 5.91 µm

Pixel area = 5.91² = 34.93 µm²

D850 pixel area

Pixel pitch = 4.34 µm

Pixel area = 4.34² = 18.84 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

Alpha a9 pixel density

Sensor resolution width = 6026 pixels
Sensor width = 3.56 cm

Pixel density = (6026 / 3.56)² / 1000000 = 2.87 MP/cm²

D850 pixel density

Sensor resolution width = 8280 pixels
Sensor width = 3.59 cm

Pixel density = (8280 / 3.59)² / 1000000 = 5.32 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

Alpha a9 sensor resolution

Sensor width = 35.60 mm
Sensor height = 23.80 mm
Effective megapixels = 24.20
r = 35.60/23.80 = 1.5
X =  24.20 × 1000000  = 4017
1.5
Resolution horizontal: X × r = 4017 × 1.5 = 6026
Resolution vertical: X = 4017

Sensor resolution = 6026 x 4017

D850 sensor resolution

Sensor width = 35.90 mm
Sensor height = 23.90 mm
Effective megapixels = 45.70
r = 35.90/23.90 = 1.5
X =  45.70 × 1000000  = 5520
1.5
Resolution horizontal: X × r = 5520 × 1.5 = 8280
Resolution vertical: X = 5520

Sensor resolution = 8280 x 5520


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


Alpha a9 crop factor

Sensor diagonal in mm = 42.82 mm
Crop factor =   43.27  = 1.01
42.82

D850 crop factor

Sensor diagonal in mm = 43.13 mm
Crop factor =   43.27  = 1
43.13

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).

Alpha a9 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 a9, take the aperture of the lens you're using and multiply it with crop factor.

Crop factor for Sony Alpha a9 is 1.01

D850 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 Nikon D850, take the aperture of the lens you're using and multiply it with crop factor.

Since crop factor for Nikon D850 is 1, the equivalent aperture is aperture.

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