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.
The sensor is the most important component of a digital camera, because it is directly responsible for capturing an optical image and converting it to an electric signal, which later gets optimized and converted to a digital image by other camera electronics. 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 12 megapixels, it literally means that the camera sensor contains 12 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 sensitivity and ability to accurately gather light in various lighting conditions. Bigger buckets are always better than smaller ones, because more light particles can be stored in those, without getting over-filled. The information about light particles is then passed on to the camera 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 extremely 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 in the modern sensors, despite the fact that the size of the sensors has pretty much remained the same.
1) 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.
2) 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.
Let’s now move on to advantages and disadvantages of both DX and FX sensors.
3) 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 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 much 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 a 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 12 megapixels, cropping an equivalent field of view from a 12 megapixel full-frame sensor would give you much smaller resolution (approximately 5-6 megapixels). However, it is a different story if you have over 25 megapixels on a full-frame sensor – cropping 12 megapixels out would yield a similar result as DX, if the size of the pixel is the same. There are a few other things to consider like depth of field, but generally, it will be the same.
- 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 small size of pixels, which results in noisy pictures and much less sharpness and detail in higher sensitivity levels. See image samples below for comparison.
- Smaller dynamic range – compared to FX, DX cameras have a smaller dynamic range, largely due to pixel size and density.
- Problems with wide-angle lenses – due to a difference in the field of view, wide-angle lenses are not so wide on a DX body anymore. A 14mm ultra wide-angle lens is more like a 21mm lens when compared to a full-frame camera, which means that you can fit a lot less in your frame. This is generally not a problem in environments where you can move back and still fit more, but presents a problem when working very close to a subject in tight space environments.
- DX lens incompatibility with FX – if you have DX lenses and one day decide to switch over to FX, you will have to purchase non-DX lenses to utilize the full resolution of a full-frame camera. DX lenses do work on FX sensors, but only at half the resolution.
- Lens diffraction – DX sensors cause more lens diffraction when small apertures above f/8-f/11 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:
4) 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 D3x) and one with better sensitivity and speed (Nikon D3s) for different needs. For example, landscape and fashion photographers need large print sizes and would therefore want more resolution, while wildlife and sports photographers need the speed and low amounts of noise in dim environments.
- 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-f/16.
- 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
- High cost – large FX sensors are expensive to manufacture than DX sensors. Nikon’s FX sensor is a flagship product and the company only uses it in professional-grade DSLR cameras such as Nikon D700/D3s/D3x.
- 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 introduced specifically for FX needs.
- Size and weight – larger internal components, rugged body and professional electronics all add up to the weight, making FX cameras the heaviest in Nikon’s line of DSLRs. With the release of the D700 DSLR that has a similar size and dimensions to D300s, Nikon has diminished the gap between top of the line DX camera and FX, however, the difference is still quite large when compared to entry-level DSLRs such as Nikon D3000/D5000.
5) DX and FX – high ISO image samples
Now let’s move on to the good stuff – a real image comparison between DX and FX sensors in high sensitivity (ISO) levels. In this example, I used a Nikon D300, D700 and D3s cameras and tested each at ISO 800, 1600, 3200 and 6400. Images from the Nikon D3 would look identical to the ones from D700, which is why it was not included in the test. Here is the sample are that 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 through our image viewer. 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. The first generation Nikon FX sensors from D700 and D3 are about 1.5 stops better than DX counterparts, while the second generation D3s FX camera is over 3 stops better than DX. The size of the sensor and pixels within the sensor is extremely important and FX shows that it is a far more capable sensor than DX when it comes to noise, dynamic range and other factors.
The big question that everybody asks at one point or another, is if FX is so much better than DX, will DX be eventually phased out and completely replaced by FX? My answer is probably not for now, definitely not until the cost of FX goes down significantly. Nikon will probably continue producing and selling DX lenses for a number of years.
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.
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