Some of the most frequently asked questions from our readers are around DX and FX format sensors. What are DX and FX and how are they different? 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 similar to the sensitivity of film, also known as “ISO” in photography. Although digital camera sensors do not change sensitivity when camera ISO is adjusted (see our ISO article for more information), manufacturers and photographers still often say “ISO sensitivity” to keep things simple and easy to understand for those who transitioned from film to digital.
Increasing camera ISO comes at a price – high ISO levels ultimately decrease image quality. This degradation of image quality is first visible as “grain” or “noise” in the pictures, followed by loss of detail, sharpness and color. As ISO is increased, it also significantly reduces dynamic range. Incredibly, 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.
The sensor is the most important component of a digital camera, because it is directly responsible for capturing an image. Just like your computer screen, sensors contain millions of pixels, except they are there to collect light, not display it. When you see a digital camera with 36 megapixels, it literally means that the camera sensor contains 36 million tiny pixels for the sole purpose of gathering light.
Think of those pixels as buckets that attract light particles – the larger the bucket, the more light particles it can store in a given amount of time. These buckets are known as “photosites” and their size plays a huge role in sensor’s ability to accurately gather light in various lighting conditions. Once an image is captured, the sensor data is passed on from the sensor to the image processor, which assembles a digital image starting from the first pixel all the way to the last. And all of this happens in a matter of milliseconds!
While larger pixels (or bigger buckets) work best for sensors, they are also expensive to manufacture. To keep the costs low and product accessible to a broader customer range, many camera manufacturers produce smaller sensors. Obviously, as the size of the sensors decrease, so do the number of pixels. To combat this problem, manufacturers have been cramming more and more pixels into tiny sensors while simultaneously increasing the efficiency and throughput of each pixel. Unfortunately, this resulted in a “megapixel race” among the manufacturers and we are seeing more and more pixels on modern digital camera sensors, despite the fact that the size of the sensors has pretty much remained the same.
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, semi-professional and even professional cameras. Obviously, the number of megapixels went up significantly with the latest DX sensors having 24 megapixels, 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 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 35mm lens appeared to have the same field of view as a film photographer with a 50mm lens and nobody wanted to accept this change as “normal”.
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 / full-frame digital cameras. 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 35mm film? That’s why it has been quite common among photographers to compare this new field of view difference relative to 35mm film / full-frame digital.
What is FX?
In August of 2007, Nikon released its 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. 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 image quality was to increase the sensor 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 2.4x, thus having much larger photosites. What this meant, was that the sensor could have higher sensitivity levels without introducing much noise and artifacts, while simultaneously being able to yield better dynamic range.
With the full-frame FX sensor, the terms “crop factor” and “equivalent focal length” are no longer meaningful, because an FX sensor is the same size as 35mm 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 field of view, not a magnified one like with DX sensors.
Let’s now move on to advantages and disadvantages of both DX and FX sensors.
Advantages and Disadvantages of DX Format
Let’s start with DX. What are the advantages and disadvantages of DX formats?
Advantages of DX Format
- Cost – obvious advantage, because the sensor is much cheaper to manufacture.
- Lens sharpness and vignetting – since DX sensors use the center of the lens and discard the corners, many professional lenses will perform extremely well on DX, because the center of the lens is always optimized for sharpness than the extreme corners. Vignetting is also typically much less pronounced on DX bodies than on FX, again due to corners not being used. For example, the older version of the Nikon 70-200mm VR II lens performed beautifully on DX bodies and quite poorly on FX bodies, which is why Nikon had to update it with a better version for full-frame cameras.
- Low-cost lenses – since the corners are cut off for the DX format anyway, manufacturers started offering smaller and more compact lenses for DX sensors that cost less than regular lenses for film and full-frame sensors.
- Reach – this part is a little controversial, again due to comparison in the field of view between DX and FX sensors, but due to the size of the sensor and its crop factor, DX sensors generally provide better reach than full-frame sensors. Some people say “well, you could simply crop an image from a full-frame sensor and have the same result as what DX provides”, which is not true, mainly due to megapixels and pixel size. If a DX sensor is 24 megapixels, cropping an equivalent field of view from a 24 megapixel full-frame sensor would give you much less resolution in comparison.
- Size and weight – cameras with DX sensors are generally smaller and lighter than cameras with FX sensors, because full-frame sensors are currently only being used on high-end professional cameras that are bigger and heavier.
Disadvantages of DX Format
- Noise in high ISO levels – the biggest disadvantage of DX, as I pointed out above, is the smaller size of pixels, which results in noisy pictures and much less sharpness and detail at higher ISO levels. See image samples below for comparison.
- Less dynamic range – compared to FX, DX cameras typically have less dynamic range.
- Problems with wide-angle lenses – due to differences in field of view, wide-angle lenses are not as wide on a DX body anymore. A 14mm ultra wide-angle lens is more like a 21mm lens when compared to full-frame, which means that you can fit a lot less in your frame.
- DX lens incompatibility with FX – if you have DX lenses and one day decide to switch over to FX, you will have to purchase full-frame lenses to take advantage of the full-frame sensor. DX lenses do work on FX sensors, but only at half the resolution due to smaller image circle.
- Lens diffraction – DX sensors cause more lens diffraction when smaller than f/8 are used.
- Smaller viewfinder size – due to a smaller mirror and pentaprism/pentamirror used on DX cameras, the viewfinder on DX is smaller and not as bright when compared to FX.
Mirror size differences between D300 and D700:
Advantages and Disadvantages of FX Format
Now how does FX compare to DX?
Advantages of FX Format
- Scalability – due to the large size of the sensor, FX format allows two different configurations: one with lots of resolution (Nikon D850) and one with better sensitivity and speed (Nikon D5) for different needs. For example, landscape and fashion photographers need large print sizes and would want more resolution, while wildlife and sports photographers need the capabilities of a fast-action camera like the Nikon D5.
- Higher sensitivity and lower noise – as I have pointed out above, pixel size plays a significant role in sensitivity levels of the camera, along with controlling noise levels at high ISOs. For example, Nikon D700 (FX) has a similar number of pixels as Nikon D90/D300s (DX) and yet the pixels on the D700 are much bigger in size than on D90/D300s. So, if you were to compare ISO 800 on these cameras, the Nikon D700 image would look much cleaner compared to Nikon D90/D300s.
- Large dynamic range – again, bigger pixel size allows collecting more light particles, which results in larger dynamic range when compared to DX.
- No field of view issue – with FX, forget about such things as “crop factor” and “equivalent focal length” – you get a similar field of view as if you were shooting film.
- Lens compatibility – FX lenses are backwards compatible with DX lenses, meaning that they will work perfectly on DX bodies as well.
- Lens diffraction – compared to DX, lens diffraction is typical to 35mm film and starts to affect image sharpness at smaller apertures above f/11.
- Larger and brighter viewfinder – large sensor means large mirror and pentaprism, which means a large and brighter viewfinder. Focusing with a large viewfinder is much easier, because you see more details.
- Wide is truly wide – an ultra wide-angle lens such as Nikon 16-35mm f/4 is not really that wide on a DX body, because of the crop factor. This problem goes away on FX and you get the true 16mm field of view as you would if you were using 35mm film.
Disadvantages of FX Format
- Cost – large FX sensors are more expensive to manufacture than DX sensors.
- Lens sharpness and vignetting – because FX utilizes a much larger area than DX on the lens, corner performance on lenses might become an issue, although Nikon has been updating their lens line and releasing new lenses that deliver outstanding corner performance for FX sensors. For example, the Nikon 14-24mm f/2.8G and Nikon 24-70mm f/2.8G lenses were both designed specifically for the full-frame sensor.
- Size and weight – larger internal components add to the weight, making FX cameras typically heavier than their DX counterparts.
DX and FX – High ISO Image Samples
Now let’s move on to image comparisons between DX and FX sensors at high ISO levels. In this example, I used a Nikon D300, D700 and D3s cameras and tested each at ISO 800, 1600, 3200 and 6400. Here is the sample I used for the test:
I cropped the lower center portion of the image from each image. I used the Nikon 17-35mm f/2.8D lens @ 35mm for this test with the default camera settings and shot in RAW. In order to get the same field of view on the Nikon D300 camera (due to 1.5x crop factor), I had to change the focal length to approximately 23mm on the lens. The below images are 100% crops and they are NOT resized in any way, so the sharpness and noise levels are somewhat accurate. Each image is tagged with the camera and ISO information and I highly recommend clicking on the images to be able to compare them at full size. EXIF data is also preserved for those who want to see the camera settings. High ISO noise reduction was set to “Normal” in all cameras. No sharpening was applied to any of the images. I did not bother comparing ISO lower than 800, because this is a high ISO test. One thing to note though, is that Nikon D300 has a little more noise between ISO 200 and 800 compared to Nikon D700 / D3s.
The difference between DX and FX is already pronounced at ISO 800. The image from the Nikon D300 DX sensor looks looks noisy and we are beginning to lose a little bit of sharpness. Nikon D700 and D3s look almost identical with no visible noise.
At ISO 1600, the Nikon D300 is extremely noisy and there is clear evidence of loss of sharpness and detail in the image. Nikon D700 starts having a little bit of noise in the shadows and Nikon D3s is still very clean.
The situation at ISO 3200 changes dramatically. Nikon D300 looks pretty bad, while Nikon D700 is still retaining sharpness, but has some noise in the shadows. Nikon D3s is shining again with the least amount of noise in the picture.
At ISO 6400, the image from Nikon D300 is unusable. Nikon D700 has a considerable amount of noise and starting to lose some sharpness, while D3s has a touch of noise but retained all sharpness and details.
As you can see, the difference between DX and FX is substantial. If we measure the above in full stops, the difference between DX and the most current FX sensor is around 3 stops. Take a look at these two images for comparison:
The image on the left is Nikon D300 at ISO 800 and the image on the right is Nikon D3s at ISO 6400! When I look closely, the image from the Nikon D3s actually looks sharper than the image from D300, which means that there is even more than 3 stops of difference between the two. In addition, despite the fact that I used the same color profile, white balance and saturation levels on both images, the image from the D3s has better colors.
As I have explained in this article and demonstrated with the above image samples, the difference between DX and FX sensors is quite clear when it comes to overall image quality. Depending on the generation of the cameras you are comparing to, differences could range from 1 stop all the way to 3 stops (as in the example above). The size of the sensor is obviously important and FX shows that it is a far more capable sensor than DX when it comes to things like noise and dynamic range. In addition, you have to factor in differences in field of view when using lenses. With FX / full-frame cameras, what you see is what you get when it comes to lenses and their focal lengths. Whereas with DX cameras, you have to apply the crop factor math in order to understand differences in field of view.
Lastly, don’t forget that whether you shoot with DX vs FX or vice-versa isn’t all important for making stunning pictures. Things like light, subject, emotion, composition and post-processing technique are far more important and those are the things you should really pay attention to.
I hope my article will help you to clearly understand the difference between the two formats and remove all confusion around DX and FX sensors. Please let me know if you have any questions in the comments section below.