Some of the most frequently asked questions from our readers are around DX and FX format sensors. What is DX and FX? What are their differences? Which one is better and why? If you have similar questions and want to get a clear understanding about these formats and their differences, along with seeing actual image samples from both, this article is for you.
Before diving into sensor formats, it is first important to understand what a sensor is and what it does in a Digital SLR camera. It is easier to understand how sensors work by comparing them with the human eye. The lens in front of the camera essentially functions as the cornea of your eyes, gathering ambient light and passing it to the iris. The iris then expands or shrinks, controlling the amount of light that enters the retina, which functions almost exactly like a camera sensor. The retina is light-sensitive, meaning it can adjust its sensitivity based on the available light. If there is too much light, it decreases its sensitivity, while automatically increasing the sensitivity in a dim environment, so that you could see in both extremely bright and extremely dark conditions. Remember what happens when you come out of a dark place to a very bright, sunny environment and vice-versa? Either your eyes will hurt and everything will seem too bright, or you will have a hard time seeing at all – due to sensitivity of the eyes that have not yet adjusted for the new environment. The sensitivity of your eyes is just like the sensitivity of the sensor, also known as “ISO” in photography. But sensitivity comes at a price – high sensitivity levels ultimately decrease image quality, similar to when you have a hard time seeing in a very dark environment. This degradation of image quality is first visible as “grain” or “noise” in the pictures, followed by loss of detail, sharpness and color in extreme levels of sensitivity. When I say “extreme”, I mean extreme to the digital camera, not human eye. Even with all of the latest advancements in sensor technology, cameras are not even close to seeing the range of light the human eye can see in various environments.
WHAT IS DX?
When Nikon entered the digital world of SLR photography, their first Nikon D1 DSLR had a smaller sensor to make it more accessible to professionals (it sold for $5,850 when it was announced). It was about 2/3 of the size of the 35mm film and it only had 2.66 megapixels. The camera quickly gained popularity and more updates of the same DSLR followed – some with more resolution and others with more speed. Nikon eventually dubbed the smaller sensor “DX”, which is approximately 24x16mm in size and is still being widely used in all entry-level (Nikon D3000/D5000), semi-professional (Nikon D90) and even professional (Nikon D300s) cameras. Obviously, the number of megapixels went up significantly with the latest DX sensors having 12.3 effective megapixels (4,288 x 2,848 resolution), which means the pixel size has also equally decreased, resulting in higher pixel density. Nikon has been able to do so because of new advancements in sensor technology, better noise-reduction algorithms and more processing power.
Historically, all digital sensor formats have been measured and compared against 35mm film. In the case of DX format, due to the sensor being smaller than 36x24mm (size of 35mm film), the subjects appeared slightly more magnified when compared to film. This was normal for the DX format, because smaller sensor meant that a smaller area of the lens towards the center was to be used and everything else discarded. However, photographers kept on comparing this difference in field of view or angle of view to the traditional film and new terms such as “crop factor” and “equivalent focal length” were born. Why did this happen? Because a photographer with a DX digital camera using a 50mm lens appeared to have the same view as a film photographer with a 75mm lens and nobody wanted to accept this change as “normal”, again, relative to film.
Nikon DX sensors, for example, have a crop factor of 1.5x. What this means, is that relative to 35mm film, the image will appear enlarged by approximately 50%. So shooting with a 24-70mm lens is “equivalent” of shooting with a 36-105mm lens on a film body. This is where things got messy and people started getting confused about focal lengths and sensor sizes. How can you say that a lens is longer in focal length with a DX sensor, if the physical property of the lens has not changed? A 24-70mm lens is a 24-70mm lens no matter which camera body it is on and no sensor can change that. The whole “equivalent to mm” verbiage can be too confusing, because it is equivalent only relative to 35mm film. At the same time, how do you explain that a 200mm lens on a DX sensor has an equivalent field of view of a 300mm lens on film? That’s why it has been quite common among photographers to compare this new field of view problem with film.
WHAT IS FX?
In August of 2007, Nikon released the long awaited full-frame Nikon D3 FX camera with 12.1 megapixels. It was the first Nikon DSLR to have a 35mm equivalent digital sensor that measured approximately 36x24mm in size with a 4256×2832 resolution. Nikon realized that cramming more pixels into a tiny DX sensor was not helping in low-light situations and the only way to increase the sensitivity of the sensor was to increase the pixel size. The 36x24mm full-frame sensor is more than twice larger in size than a 24x16mm DX sensor. By keeping the number of megapixels low relative to the size of the sensor, Nikon increased the pixel size by 2.4 times, thus having much larger photosites to store light particles. What this meant, was that the sensor could have higher sensitivity levels and see a much larger range of light from blacks to whites, known as “dynamic range“.
With the full-frame FX sensor, the terms “crop factor” and “equivalent focal length” are no longer valid, because an FX sensor is the same size as film. This means that if you took a film camera and a full-frame digital camera, mounted 24-70mm lenses on them and took pictures of the same subject, both would produce a similar view, not a magnified one like with DX sensors.
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