I am an enthusiast and currently I shoot with Nikon D90. I am in the process of upgrading the body, but little confused over the same generic question of FX vs DX. I know that an FX sensor delivers better dynamic range, high ISO capacity and more control over depth of field than a DX sensor. However, if I shoot with a FX camera in DX mode does it deliver the same high ISO and dynamic range performance?

2 Answers 2


DX lenses project a smaller image circle than FX lenses, smaller than an FX sensor. DX mode allows you to use an area the size of a DX sensor in the center of your FX sensor so the DX lens image circle will cover this area. Since each photosite in this area is still its full FX size, you will retain all the ISO and dynamic range capabilities of an FX sensor. However, since you are only using about an area about 45% of the full FX sensor, you will lose about 55% of your megapixels. This means a 36MP FX camera will produce 16.2MP images in DX mode, and a 24MP FX camera will produce 10.5MP images in DX mode. In addition, in DX mode, you will experience the same crop factor effect on your focal length. This means a 35mm FX lens on an FX body will give the angle of view expected, but a 35mm DX lens on a FX body will give an angle of view approximately like that of a 50mm FX lens on an FX body, just as that lens would do on an DX body.

If you have a large investment in DX lenses, DX mode can be a reasonable bridge, but you will not be using about half of your very expensive pixels, so if you have fully committed to moving from DX to FX, you should seriously consider selling your DX and lenses and acquiring FX lenses to take full advantage of your sensor.

  • Hi, I was aware of few of these, but the megapixel part was completely unknown to me. Thanks for explaining this. My investments are mixed; I have recently bought Nikon 70-200 f/4 (I cannot afford f/2.8 now) and I have a 50mm f/1.8 lens and I am planning to sell my DX lenses (Tamron 18-270 and Nikon 18-55) and buy more FX lenses. But somehow I get fascinated with wild life photography; do you think FX body is good for that?
    – Niranjan
    Jan 21, 2014 at 8:52
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    FX bodies are good for anything (except portability and your bank balance) - if you're prepared to spend the money to get the lenses to match. What problem are you trying to solve that means you need full-frame?
    – Philip Kendall
    Jan 21, 2014 at 8:56
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    Wildlife photographers often prefer cameras with smaller sensors, because lenses with equivalent reach will usually be smaller, lighter, and less expensive for the camera with the smaller sensor.
    – Icycle
    Jan 21, 2014 at 9:03
  • @PhilipKendall often equivalent performance can be achieved with cheaper lenses on FX, especially in the wide/normal range, compare a 50mm f/1.8 lens at f/2.2 on FX against a 35mm f/1.4 wide open on DX and the much cheaper FX lens will have higher average sharpness. Depth of field will be the same and so will noise (in good light). Telephoto lenses are the exception where you pay more for FX.
    – Matt Grum
    Jan 21, 2014 at 10:29
  • Hi Philip, I currently use Nikon D90 and with this I am not able to take photos in not-so-bad conditions (You can see http://500px.com/photo/58377286). I want to upgrade my camera body and mainly looking for D7100 or some FX camera (like D610). Hence, I am collecting the information.
    – Niranjan
    Jan 22, 2014 at 2:06

You're using the same sensor pixels, so in many ways, yes you will get the same high ISO performance and dynamic range - but that applies only for a pixel by pixel comparision. If you're looking at a fixed print size, which is generally a much more useful comparision, then you won't get the same performance because you'll have less downscaling going on (see Icycle's answer for details as to why).

What you will definitely lose is the better depth of field control of the FX sensor - as you're effectively reducing yourself to a DX sensor, you're back to the more limited depth of field control you get there.

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