DX vs FX Crop Sensor
Which is right for you
To baseline the discussion we will consider a comparison between two similar Mega Pixel sensor cameras, one being a DX (23.5 mm x 15.6 mm) and the other a FX sensor (35.9 mm x 23.9 mm), the DX & FX having the same number of pixel resolution - so, is there a difference?
Right off the bat you notice the a size difference as illustrated in the diagram, yellow portion represents the sensor, the DX sits well within the larger FX sensor, this matters to some degree throughout the article. When I say sensor size I am speaking about the physical size.
Sensor Size VS Image Quality: Let’s dive into this urban legend. Sensor size matters to some degree for a number or reasons, but is not necessarily a big factor in everyday use. What drives image quality if we remove the lens as a factor? Consider two sensors both having 24MP. Sensor (1 is DX), in order to cram 24 million of light gathering diodes onto a fixed size sensor each light gathering diode has to be of a certain size – see where I am headed with this? So DX sensors as compared to the FX sensors will in most situations have smaller light gathering diodes. On FX sensors there is more room on the larger sensor and thus the light gathering diodes can be larger. Larger diodes normally have better light sensitivity and dynamic capabilities – as a general statement. In most everyday use for posting photos on websites, or producing regular sized prints you will be hard pressed to notice ANY real difference between DX & FX, otherwise pros would not use crop sensor cameras along with their pro bodies. Where things begin to become more noticeable is when we drive the cameras into higher ISOs & more difficult lighting situations, then try to produce very large prints or 100% closeups. Why do smaller sensors begin to show noise at comparable ISOs/shooting situations?
Factor in the “Engine” of the Camera: Everyone knows newer software and hardware normally makes images look better, as the cameras technology progresses so does the ability of the processor to deal with “noise & artifacts” more quickly, and more efficiently, camera manufactures work hard to optimize algorithms that help produce better images. What most of us are starting to see is the gap shrink between sensor sizes when used within the “normal” casual range or use, because we have newer faster “camera processors" both Canon and Nikon take turns leap frogging each other. Electronics have a lot to do with the image quality, as light gathering diodes are more closely packed onto smaller sensors so increases the “noise”. Back in the day, medium format cameras produced better images than 35mm, the ratio of negative to print size; today we are dealing with electronics and variations of sensor sizes coupled with the density of diodes on the sensors. So, that larger sensor can have larger diodes and usually edges out in performance once you move into higher ISOs, and while newer camera processors make smaller sensors perform better they also make larger sensors perform better.. Win Win for everyone. So nowadays, you see DX cameras produce quality on par with FX especially if the FX is running older software/hardware.
What about the CROP Factor: The funny thing is, if you never use a FX camera and only use DX cameras, chances are you don’t even know the difference exist. It becomes noticeable when switching between "systems". Example: If you are a FX users and love using a 24mm on a FX camera you know generally what Field of View (FOV) you will get based on our past experience. When planning a shooting session we can grab a lens with confidence, knowing we will have the right FOV to capture what our intentions are. But if you change systems to a DX and slap that 24mm on a DX camera body the FOV changes because the sensor is smaller – hence the term crop factor. In this situation the 24mm will look more like a 35mm, 36mm to be exact, this is not a bad thing just different, requiring you to make this consideration when shooting DX.
Why is this? In the simplest terms possible – the image being projected from the rear lens element will exceed the boundaries of a DX sensor. The sensor will be capturing the central most portion of the image projection. An FX lens on a FX camera will project the image to the edge of the sensor capturing the entire image. See the illustration. This gives the impression of magnification on the DX sensor while the FX will show the entire image on the sensor, not a portion of it. To get the same effect with a FX you would need to zoom in 1.5 to fill the sensor. Home work example: Draw a 1 inch square and a 2 inch square, now drop a penny on the 1 inch square, and slide it over to the 2 inch square. Compared to the 1 inch square the edges of the penny will overlap on the 1 inch, while the 2 inch will include the entire penny, and if processed this digitally, Abes head would appear larger on the smaller sensor, because a portion fills up more space than on the 2 inch square.
So what is the difference between FX and DX lens: Not much really at least for Nikon, at the end of the day, both serve the same purpose when used with the intended camera system. DX lenses are engineered for DX cameras body, are normally smaller, lighter Cheaper :) as compared to the larger FX lenses (larger glass=more weight & cost). In most situations FX lenses work perfectly fine on DX cameras, while all DX lens may not work properly on a FX camera body due to the image projection from the rear DX lens element was not designed for FX sensors, thus you may have dark/black corners when using some DX lens on FX cameras, Tamron 11-20mm (DX) is a good example, this lens is designed for DX cameras, the lens will not fully cover the FX sensor until you zoom out to 16mm and beyond, it works fine at 16mm and beyond but not at the wide end.
Depth of Field: Something else we must mention when speaking about crop sensors and lenses like the crop the DX also influences depth of field (DOF). More compressed on DX, this issue might be less of a concern for most folks. As an example using a 35mm will have a DOF more like a 50mm. Unless you concentrate on DOF as a primary objective in you photographic compositions, it will be not too much of a concern.
Does the crop factor work for me or against me: Both. Let’s take the positive first. If you like longer lens and have a passion for outdoor wildlife, bird and sports photography – you are in luck. DX cameras help get you closer. That cheaper 300mm f/4 will become a 450mm on a DX, then slap on a 1.4 TC and you’re out to 630mm 5.6 FOV.
On the down side: if you like the wide side of things, the wide angle lens also have the same crop factor, and in order to go wide you need a real wide lens. But don’t fret, the DX market has it covered, just need to be aware of the 1.5 crop when shopping for the wide lens.
Why can’t I just buy a FX camera and set it to CROP mode when I need it: Good news is, you can! Many newer FX cameras offers a CROP mode in camera. The side story to this is: consider both camera examples above as having 24mp sensors. When you set the FX camera to internal 1.5 crop mode you lose some of that wonderful 24 MP resolution & your optical view (what you see) has not changed from full frame FX mode, you may see a rectangular boundary box as you peer through the camera, but trust me, you sometimes forget you are shooting in crop mode, and anything outside the bounding box will be lost and in the heat of the moment, ooops.. While DX cameras will retain the full (sensor mega pixel) 24mp for this discussion, and your optical view will remain constant, IMHO it is best to use DX for situations needing longer lens vice a FX camera in crop mode, but it is doable with a FX.
You never answered the question, what should I get a DX or FX: Today, I don’t have a hugh argument one way or the other. My first digital camera was an Olympus 3mp camera costing $900.00, expensive at the time and I though I would never need another camera, the sensor of the Olympus was smaller than a DX sensor and I was happy with that until I got my hands on a Nikon D70 and started using my older film lens on the D70 camera. Remembering back, those first FX cameras were very expensive and the camera companies were in a race of the MegaPixels more than anything.
The fact is, nowadays you could be completely happy with either format.
If I were to do it all again, I would have skipped the Olympus and started with a FX DSLR then purchased a DX body, with lenses being primarily made up of FX since they work on the DX camera, only exception to this is a couple DX lens for light weight travel – sometimes you just want to travel without the hassle of added weight. By the way, I have CX sensor camera (even smaller than DX) @ 2.7 crop, and I enjoy using it, and at times astounds me with the speed of focus and the quality of images it produces for such a small sensor camera. This is exactly my set up today I use my FX, DX and my CX along side each other, without worries of which is better - each has benefits.
One final: Nikon is the only Camera company who most cleanly supports the use of Nikkor lenses on on their FX - DX - CX camera bodies. I can use my 600mm on my FX, my DX outright and my little CX with the FT-1 adapter.
I have a fondness for the DX and use both DX and FX sensor cameras in my photographic endeavors.
- Sigma 8mm F3.5 EX DG Circular Fisheye
- Tokina AT-X 11~20mm f/2.8 Pro DX
- Nikkor 16-35mm f/4G ED VR
- Nikkor 24mm f/3.5D ED PC-E
- Sigma 35mm F1.4 DG HSM Art
- Nikkor 45mm f/2.8D ED PC-E
- Nikkor 300mm f/4 PF ED VR
- Nikkor 400mm f/2.8 ED FL VR
- Nikkor 600mm f/4 FL ED VR