Introduction
Sensor sizes for Full-Frame and PAS-C cameras
Sensor type
Sensor resolution
Pixel area (µm²)

1. Introduction

Schematic diagram showing the lens and the sensor

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.

2. The Image Sensor Sizes

Image result for 50mm focal length in fx and dx nikon cameras
Essentially, at the heart of every digital camera is an image sensor. The lens focuses photons reflected by the scene being photographed onto that image sensor. Etched into the image sensor’s silicon are pixels (short for “picture elements”)—technically, photoreceptor or photodiode sites. Each pixel is a single point that collects the electrons, which are then interpreted into information about color and light.

Medium-format
Fujifilm GFX 50S
Hasselblad H5D-60 40.2 x 53.7mm CCD Sensor

44 x 33mm

40.2 x 53.7mm

Full Frame

26×24 mm

APS-C
(High End like D7200)

23.5×15.6 mm

Note that the full-frame sensor size is much larger than even the high end APS-C (like D7200) cameras.

Characteristics of Sensor

Sensor type	CMOS
Sensor size	35.9 x 24 mm (Nikon FX)
Sensor resolution	6038 x 4025
Pixel pitch (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.
Pixel area (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.

The main characteristics of the Image Sensor are:

Camera Feature	Nikon D7200	D610	D500	Next
Sensor Resolution	24.2 Million	24.3 million
Sensor Type	CMOS
Sensor Size	23.5×15.6mm	35.9x24.0mm	23.5×15.7 mm
Sensor Pixel Size	3.92µ	5.95 µm
Sensor Dust Reduction	Yes	Yes
Image Size	6,000 x 4,000
Sensor Dust Reduction	Yes	Yes

What does sensor pixel area mean?
In order to understand the effect of the megapixel count on a digital camera we must understand how a digital camera records a picture. Before digital cameras, still pictures were recorded on a 35mm black film (negative). This 35mm film is called full frame. With the advent of digital photography, the film was replaced by a digital sensor, usually a CMOS/CCD1 sensor. The catch however was that the sensors were much smaller than the traditional 35mm film because larger digital sensors are seriously expensive to manufacture.
In low-light, if their sensor size is identical, a camera with low megapixel count will always give a clearer image and capture more detail than a camera with a higher megapixel count.
Digital cameras with smaller sensors can make do with smaller lenses. However, a digital camera having a larger sensor will need a larger lens. This is why digital SLR cameras which have digital sensors close to the original 35mm size usually have larger lens attachments than digital pocket cameras.

Nikon is moving towards lower pixel size

Nikon D7500 vs D7200 Specification Comparison

Camera Feature	Nikon D7500	Nikon D7200
Sensor Resolution in Pixels	20.9 Million	24.2 Million
Sensor Type	CMOS	CMOS
Sensor Size	23.5×15.6mm	23.5×15.6mm
Sensor Pixel Size	4.22µ	3.92µ

The latest D7500 has got less number of pixels but larger pixel size than its older version D7200.

Remember.

In low-light, if the sensor size is identical, a camera with low megapixel count will always give a clearer image and capture more detail than a camera with a higher megapixel count.

Therefore, D7500 will perform better in low light.

With the D800, Nikon may be signaling a shift in megapixel mindset. The D800 packs a 36 megapixel sensor and pushes images with a resolution of 6144×4912 pixels. However, D5 has a 20.8 megapixel sensor. The D4 at $6,499.95 is far more costly than the D800, and is targeted toward speed shooting and a better high ISO experience.