DX vs FX focal lengths?

Discussion in 'Nikon Cameras' started by darkblue-x, Oct 23, 2017.

  1. darkblue-x

    darkblue-x TPF Noob!

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    I dont get it.
    I have a DX lens for instance that is Nikkor 16-85mm and they say that the 16mm end is a 24mm equivalent on FX, I believe.
    Which brings me to my question, an FX lens, the 24-120mm...what length would that be exactly in DX terms. How do you calculate these?


     
  2. JonA_CT

    JonA_CT TPF Supporters Supporting Member

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    For a Nikon camera, multiply the focal length by 1.5 to get the equivalent field-of-view.
     
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  3. darkblue-x

    darkblue-x TPF Noob!

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    To see if I understand...So then an FX focal length of 24-70mm would look like 16-46 on a DX?
     
  4. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    No. A 24-70 would be the equivelant to 36 (24x1.5) - 105 (70x1.5).
     
    Last edited: Oct 30, 2017
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  5. benhasajeep

    benhasajeep No longer a newbie, moving up!

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    Nope other way

    24-70 on a DX camera would act like a 36-105mm lens on full frame camera (field of view FOV).
    A 200mm lens on your camera would have the same scene in your viewfinder as a 300mm would on a full frame.
     
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  6. darkblue-x

    darkblue-x TPF Noob!

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    Okay what about a prime lens then?
    I have a Nikon 35mm Dx f/1.8..
    Would an Fx 35mm prime be the same or are they the same whether on dx or fx
     
  7. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Focal length is focal length is focal length. That NEVER changes.

    What changes is the field of view. A 35mm prime will provide the same FOV as a 16-85 zoom set to 35mm.
     
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  8. benhasajeep

    benhasajeep No longer a newbie, moving up!

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    Focal length on the lenses are the same. What DX and FX designate is the size of the image circle they produce. Since crop sensor cameras have smaller sensors the image circle does not need to be as large. So the DX lens is designed for that smaller image circle. But the lens focal length stays the same.

    For example I can put a DX 18-55 lens on a full frame D800. It will be a 18mm to 55mm zoom on that camera. But it will not cover the entire sensor. So, any lens you have on your camera you multiply by 1.5 to get the equavilant view on a full frame camera.
     
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  9. Braineack

    Braineack Been spending a lot of time on here!

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    Are you ever going to use an FX body?
     
  10. Designer

    Designer Been spending a lot of time on here!

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    Never mind all that because it hardly matters one whit in the real world.

    You see; there are just way too many people out on the internet who worry about such things and make statements and videos to try to confuse the newbies.

    The reality is that; if your lens fits your camera, you can use it. Unless you already have some visual reference of how a given lens will give you what field of view, there is no practical reason to be concerned about the mathematical relationship of a larger sensor vs. a smaller sensor. The field of view is what it is, nothing more complicated than that.

    I'm going to make a brash assumption that you really don't already have a pre-conceived visual reference of what a certain field of view should look like, so my advice is to simply ignore all that ratio stuff, and don't let the internet take you for a ride. Just enjoy whichever lenses you have or wish to purchase.

    Field of view: It is what it is.
     
    Last edited: Oct 24, 2017
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  11. Braineack

    Braineack Been spending a lot of time on here!

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    exactly, how your lens looks/performs on someone else's camera has no bearing whatsoever on you. so don't worry about it.
     
  12. Tomasko

    Tomasko No longer a newbie, moving up!

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    Sure, but it's an important concept to understand if you're trying to learn photography more deeply than just point&shoot.
     

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