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DX to FX equivalent

Discussion in 'Lens Matters' started by shinerB, Nov 2, 2017.

  1. shinerB

    shinerB New Member

    I'm sure this has been covered before, but I just want to be sure before I buy a new lens. I've been using my old DX lenses on an FX body. The lens I use the most is the 35mm, so I'd like to get an FX lens that has approximately the same field of view. Am I right that this would be a 50mm FX?
     
  2. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    35mm on DX roughly equals 50mm on FX. 35mm on FX roughly equals 24mm on DX.
     
  3. shinerB

    shinerB New Member

    Thanks. So to get the equivalent field of view that I've been getting from using my 35mm DX lens on my FX body, I'll need a 50mm FX lens?
     
  4. spinno

    spinno Well-Known Member

    Well it depends. Does your FX camera have a Crop Mode where if non-FX lenses are used it reduces the used sensor size down to APS or does the image cover all the image circle without vignetting
     
  5. ChrisNewman

    ChrisNewman Well-Known Member

    I have a D800 and regularly use DX lenses on it (they’re lighter to carry when I want an alternative to my 24-70mm). By default the D800 crops these lenses to DX sensor size, but I can override that in the menu if I want. So if the OP hasn’t been overriding the automatic crop, a 35mm lens on an FX Nikon body will almost certainly have given a field of view equivalent to about 53mm. (I believe the new D850 blanks out the periphery of the viewfinder with a DX crop, whilst my D800 only shows a black frame, but if the image has a much smaller field of view than shown in the viewfinder, it’s been cropped. Checking the pixel count would be another way to find whether the image is cropped.)

    Chris
     
    spinno likes this.
  6. spinno

    spinno Well-Known Member

    So then the question I have is....would the image produced by the DX 35mm be more like the image produced by the 35mm FX or 50mm FX? My understanding based on the Pentax K 1 (without seeing one or using one) is that the crop acts as though it was producing an apsc image rather than a crop of a full size (35mm film equivalent) 35 mm lens. It's all too much for my one little brain cell (about apsc size)
     
  7. shinerB

    shinerB New Member

    Thanks for the replies. I've been using a D810 with the auto DX crop on, and the DX (1.5x) image area. I only get vignetting when using a wide- angle lens.
     
  8. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    Just to be clear - a 35mm lens is a 35mm lens is a 35mm lens. If you mount a 35mm lens on an APS body (which Nikon calls a DX) then you'll get a similar angle of view to what you get if you mount a 50mm lens on a full frame body (which Nikon calls a FX). HOWEVER some full frame bodies can automatically recognise that the lens is from their DX range. They will then pretend to be DX bodies and your 35mm lens will once again give an angle of view similar to a 50mm FX lens. Does that make sense?
     
    ChrisNewman likes this.
  9. spinno

    spinno Well-Known Member

    Does to me!
     
  10. shinerB

    shinerB New Member

    That makes sense. Thanks. So it's a 50mm FX lens I'll be after.
     
  11. GeoffR

    GeoffR Well-Known Member

    The OP did use the term "Field of view" when asking the question.
     
    Roger Hicks likes this.
  12. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    Could you explain what point you're making? :confused:
     
  13. GeoffR

    GeoffR Well-Known Member

    Your response appeared to suggest that the OP was unaware that a 35mm lens is always a 35mm lens. I was merely pointing out that this isn't the case.
     
    Roger Hicks likes this.
  14. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    We've had previous enquiries on this subject that have shown people don't always get that. I think it's because of the frequent use of the term "equivalent focal length" in adverts and on forums. I don't think it harms to assume that readers new to the subject might need to have the point made.
     
    ChrisNewman and Roger Hicks like this.

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