DX vs FX focal lengths?

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

  1. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    The angle of view (what you see through the viewfinder and get on the sensor) of DX at 16 is equivalent to FX at 24mm.

    To convert the angle of view of a DX to FX you multiply the DX focal length by 1.5
    To convert the angle of view of a FX to DX you divide the FX focal length by 1.5


    NOTE focal length is always the same, a DX 16mm lens and an FX 16mm lens on a DX camera body will give you exactly the same angle of view. With Nikon many of their FX camera bodies can let you use a DX lens on it by activating only a portion of the central area of the sensor, as a result you'd get the DX lens performing as if it were on a DX camera body

    FX = fullframe or 35mm
    DX = crop sensor (cropped in terms of comparing it to 35mm)


     
  2. Designer

    Designer Been spending a lot of time on here!

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    You can get fairly close with the 24-70.

    No.

    Wider.
     
  3. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    Your viewfinder may not show 100% of what your sensor sees. It may only show 95%. So composition of a subject has to take that into consideration if no post processing.

    The MIRROR's size is based on the sensor size. Thus the VIEWFINDER will only show you what the Mirror reflects. Technically you could have a mirror 3x the size of the sensor and the viewfinder would show you a gigantic area of which most won't be captured.

    Generally, The lower end camera the darker and less of the actual subject size is shown - it's not by much but it's still there.
    viewfinder info ==> APS-C field of view

    But that mirror size, based on the Sensor size - the sensor defines the FOV which may change what a lens "sees".

    If you have a lens that is a 24-70 that lens is designed as a 24mm-70mm.
    On a Full Frame Camera which is considered 1x (as it's the base) makes that lens FOV as a 24-70.
    On an APS-C camera which is considered 1.5x makes that lens FOV as a 36-105.

    To compensate on a APS-C camera you need a 16mm lens to get the (16x1.5) FF 24mm equivalent on a FF sensor.
    ==> DX Lens Focal Lengths
     
  4. darkblue-x

    darkblue-x TPF Noob!

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    So then 24mm FX is the same FOV as 16mm on DX?
     
  5. Tomasko

    Tomasko No longer a newbie, moving up!

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    Yes. It's really just the most basic multiplication/division...
     
  6. darkblue-x

    darkblue-x TPF Noob!

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    soooooo then the FOV that an FX lens 24-70 gives off is similar to a standard zoom FOV on a DX of 16-45 or 50?
     
  7. Tomasko

    Tomasko No longer a newbie, moving up!

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    70 / 1.5 = roughly 46,67
     
  8. Ysarex

    Ysarex Been spending a lot of time on here!

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    Yes.
     
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  9. darkblue-x

    darkblue-x TPF Noob!

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    Okay finally. I made that calculation weeks ago, everything else ITT served to confuse me further.

    that's an okay focal length on the lower end, lacking a bit on the longer end though...
    I saw that nikon makes a 24-120 lens though.. should I move on to FX maybe I should get that.
    third party lenses are the same thing arent they?
    and what if its a PRIME FX lens like 35mm? are they the same between DX and FX? Id imagine they make the DX lenses to make the FX equivalent in DX format and same with FX.
    I may just be best going to the Camera store, I am a visual learner it may be easier having someone show me with the cameras and lenses physically for it to fully compute.
     
  10. Tomasko

    Tomasko No longer a newbie, moving up!

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    Focal lengths are (to my knowledge) always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.
     
  11. darkblue-x

    darkblue-x TPF Noob!

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    I'm confused again because the FOV of 16mm DX on FX is 24mm.
    So then 35mm DX on FX is???? 50mm FX? To get a prime with same FOV as my 35mm DX do I have to buy a 50mm on FX?
     
  12. Ysarex

    Ysarex Been spending a lot of time on here!

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    No. My compact is here on my desk. The zoom lens is inscribed 5.2mm - 17.2mm, f/1.4 - 2.7. It has an equivalent FOV on the wide end that's the same as a 24mm on a FX camera or a 16mm on a DX camera.

    There have been camera manufactures that inscribed lenses with FF equivalent focal length values --a horribly bad idea -- but typically they note that when they do it.

    Joe
     
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