DX vs FX focal lengths?

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

  1. Ysarex

    Ysarex Been spending a lot of time on here!

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    Yes.

    Put a 35mm on your DX and a 50mm on your FX and stand in the same place with both and see the same image through both.

    Joe


     
  2. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    Think of it like this; focal length is an optical property of the lens alone
    Sensor/film size is a property of the camera alone.

    It's only when you combine the two that you get the angle of view.

    Most photographers speak in 35mm sensor equivalents for angle of view because it is the most widespread and popular of all the film sizes. So most people know what the angle of view looks like so it acts as a common ground. That said companies generally only mark lenses in actual focal length; where its equivalent they state it (equivalents tend to be more stated on compact cameras because it sounds more impressive and is easier to relate to than their actual focal lengths.
     
  3. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    IGNORE the FX / DX thing in regards to the lens.

    the FX / DX thing has to do with the SIZE of the image being projected on the sensor. Not with any distinction of the lens.
    A 50mm lens is a 50mm lens whether it is for a DX or a FX sensor.

    The distinction is the SIZE of the sensor.
    If you are using a 50mm lens a FX sensor will capture a large sized image (which is considered 1x) of that image circle from the lens. A DX will capture a smaller portion of that image, about 1.5x smaller.

    because of that, when you compare the two image at the SAME SIZE Visually, the DX one is about 1.5x cropped or larger than it's respective size on a FX image. The DX will have a smaller portion of the FX image.

    does that make any sense.

    Thus, as I had posted if you look at the chart on this post ==> DX Lens Focal Lengths

    Now, a lens designated DX will, in order to save money, make the glass elements smaller because the sensor is smaller. Since the sensor is smaller it only needs a smaller image circle. Thus the lens can be smaller with all else being equal.

    That's why really small sensors can have really small lenses.
     
  4. Tomasko

    Tomasko No longer a newbie, moving up!

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    What are you confused about? Once again, it's just a simple multiplication and division.

    FOV of a 16mm lens on a DX body = FOV of a 24mm mounted on a FX body

    Crop factor of a DX camera is 1.5, so if you have a lens with a certain focal length and you have a DX body, just multiply the values to know what FOV would it correspond to on a FX body.

    Seriously, this is primary school Math...
     
  5. darkblue-x

    darkblue-x TPF Noob!

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    16mm dedicated dx = 24mm fx. conversely 24mm fx brought back to dx cam is 36mm. thats what confused me.
     
  6. Braineack

    Braineack Been spending a lot of time on here!

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    yes.

    since 35mm focal length x 1.5 crop factor = 52.5mm FX equivalent

    upload_2017-11-9_11-15-15.png



    NO! come one. this is basic math. do they not teach math in school anymore?

    if: 16 * 1.5 = 24 how can 16 * 1.5 also = 36

    this is like 3rd grade math:

    if: X * 1.5 = Y

    and Y = 36, solve for X.

    X * 1.5 = 36

    X / 1.5 = 36 / 1.5

    X = 24
     
    Last edited: Nov 9, 2017
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  7. Designer

    Designer Been spending a lot of time on here!

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    I guess we'll keep trying until you say "stop, I completely understand now. Don't keep trying to explain any further!"

     
  8. darkblue-x

    darkblue-x TPF Noob!

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    Tokina 11-20mm f/2.8-22 Wide-Angle-Zoom Fixed Zoom Digital SLR Camera Lens, Black (ATXAF120DXN)

    by Tokina


    1 customer review



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    • F-Mount Lens/DX Format. 16.5-30mm (35mm Equivalent)
    • Aperture Range: f/2.8 to f/22. P-MO & Glass-Molded Aspherical Elements
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    F MOUNT ON A DX CAMERA SIR.

    16MM DX dedicated is 24mm on FX dedicated.

    16mm dx=24mm fx

    to reverse FX dedicated 24mm put on DX is 36mm.

    k? at this point youre misunderstanding me. im talking about the different mounts at the same time.
     
  9. Tomasko

    Tomasko No longer a newbie, moving up!

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    Mount doesn't matter at all. AT ALL.

    The text you posted even tells you what does it translate to when converted to the 35mm format (16.5-30mm (35mm Equivalent))

    And one last time:

    If you convert one format to another, you use multiplication (DX -> FX). If you want to convert back, you need to use the OPPOSITE operation = DIVISION.

    At this point I believe you're just having tremendous fun. Seriously, primary school Math.
     
  10. darkblue-x

    darkblue-x TPF Noob!

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    why its bolded and underlined clearly.
    16mm dx dedicated is 24mm fx
    24mm fx to 35mm format (dx) is 36.
    youre confused clearly or just dont like my method of explaining it
     
  11. Alan92RTTT

    Alan92RTTT No longer a newbie, moving up!

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    darkblue-x, Unless i have missed something you have one body, a D7100. If that is correct, there are a lot of details in this thread that do not matter to you.

    DX vs FX is irrelevant to you as far as what you will see when you use the lens. The FOV conversions and all the other math do not matter. FX and DX lenses will provide the exact same image on your D7100. If you want to take wider angle images get a lens with a smaller mm that what you have. If you want to zoom more get a larger mm lens.

    IF and ONLY IF you think you will get a FX body at some point in the future buy FX lenses as they will work on the FX camera.

    Ignore the DX/FX just get the size lens you want.
     
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  12. john.margetts

    john.margetts No longer a newbie, moving up!

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    Good Lord! Completely wrong.

    Focal lengths are written in respect of the focal length. If you buy a 80 mm Hasselblad lens it will be 80 mm focal length and Hasselblad do not care at all about "full frame" as their sensors are much bigger.
     
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