Fx vs do format

Discussion in 'Photography Equipment & Products' started by Zach Spencer, Jan 15, 2016.

  1. Zach Spencer

    Zach Spencer TPF Noob!

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    I am a total noob and I was wondering if a 18 mm dx lense on a dx camera would give the same field of view as a 18 mm fx lense on a fx camera


     
  2. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Well, yes and no.

    An 18mm DX lens might have a slightly wider FOV when shooting an FX body in FX mode, but when you switch to DX mode, it will be the same.
     
  3. Derrel

    Derrel Mr. Rain Cloud

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    The answer above is a rather smart-a@@ evasion of a dead-simple question.

    The question was: "
    I was wondering if 1)an 18 mm dx lens on a dx camera would give

    2) the same field of view as

    3)an 18 mm fx lens on a fx camera"

    The answer is a flat, "NO". On FX, an 18mm lens is a VERY wide-angle lens...for most of my lifetime, an 18mm lens on a 24mm x 36mm film camera would have been classed as an ULTRA wide-angle lens. An FX sensor measures almost identically to 24 x 36mm in both dimensions.

    On the smaller DX or APS-C size image sensor used in most affordable d-slr cameras, an 18mm lens has a field of view that is approximately equal to a lens of 27mm to 28mm focal length when used on the traditional 24x36mm capture area of 35mm film in the long-used 135mm format, which in today's digital SLR era is called FX by Nikon, and FF or full-frame digital by users who shoot Canon or Sony digital cameras.

    In terms of angle of view: data from http://www.tawbaware.com/maxlyons/calc.htm

    18mm focal length lens on DX camera with 1.5x FOV factor FOV in degrees: horizontal 67.4 degrees, vertical 47.9 degrees, diagonal 77.4 degrees

    18mm focal length on FX camera with 1.0 FOV factor (null) in degrees: horizontal 90.0 degrees, vertical 67.4 degrees, diagonal 110.5 degrees.

    This is a HUGE difference, by every metric.
     
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  4. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Apparently, Derrel, I missed one small but rather significant fact.

    My bad. And I admit it. It stems from the fact that many DX kit zoom lenses start out at 18mm, and there's precious few 18mm FX lenses.
     
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  5. Trever1t

    Trever1t Been spending a lot of time on here!

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    lol, everyone just chill!

    FX sensor is bigger...A DX is called a crop sensor. Searcg google for FX Vs. DX and there are pictorals that show the frame size in comparison.
     
  6. Derrel

    Derrel Mr. Rain Cloud

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    It's quite obvious that you missed two, not "one", utterly fundamental and critically important parts of a simple question.
    As you are so fond of saying, "There, FIFY". (fixed it for you)
     
  7. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    [​IMG]
     
  8. PaulWog

    PaulWog No longer a newbie, moving up!

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    This is why photography is hard to get into nowadays. "Just Google it" results in finding this kind of stuff. I will reiterate what has already been correctly said, but in a different way:

    1. An 18mm DX lens on a DX camera gets you an approximate 27mm field of view.
    2. An 18mm FX lens on a DX camera gets you an approximate 27mm field of view.
    3. An 18mm DX lens on an FX camera gets you an approximate 18mm field of view, but the borders of your image will be black. Many FX cameras automatically switch to "DX mode" when you put a DX lens on them, essentially automatically cropping the image for you to pretend to be a DX camera.

    What this means:

    If you get a 50mm lens for a DX camera, it will produce about a 76mm equivalent focal length. If you put that lens on an FX camera, you will get a 50mm equivalent focal length.

    If you get a 30mm DX lens for a DX camera, it will produce an approximate 45mm equivalent focal length. Whether a lens is made for DX or not doesn't change how it works on a DX camera, it just means it won't work on an FX camera since it's not big enough to project the light properly onto the larger FX sensor.

    Furthermore: If you want to get into it a little bit more, you need to account for depth of field changes as well. An aperture of f1.8 on DX will produce the same depth of field as an aperture of about f2.8 on an FX camera. You have a conversion of about 1.52x on Nikon, and 1.6x on Canon. You can convert your focal length and your aperture to get the equivalent full frame depth of field and field of view. However, your exposure settings do not change (If you need to shoot at f1.8 and ISO 400 and 1/100 of a second, it wouldn't matter if you use FX or DX, that would produce the exact identical exposure on either format).
     
    Last edited: Jan 16, 2016
  9. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    The problem with all this 'crop factor' and 'equivalent field of view' is that, while it made sense when digital first hit the market, it's obsolete now.

    Back in 'the day' when 35mm film was the norm for most amateurs, everyone pretty much knew how focal length and FOV were related. A 28mm had the same FOV whether you shot Nikon, Canon, Pentax, Minolta, or whatever. Only those who dabbled in other formats needed to 'do the math' to make such conversions. This was the province of pros and semi-pros. The average shooter didn't need to understand how focal length and film format resulted in a given field of view.

    Then along came digital with its smaller sensor, since marketing a 'full-frame' sensor would have been fiscal suicide. So the manufacturers came up with a simple solution.... 'Equivalent Field of View". Now, old-school 35mm film shooters could easily convert their existing focal lengths and have a reasonable idea what they would get with their fancy-dancy new digital camera. Your trusty 28mm now had the 'equivalent field of view' to a 40mm now.

    But now the problem has been overcomplicated with the proliferation of 'full-frame' bodies. This is causing the 'crop-factor' idea to implode. A simple, elegant and easy-to-remember solution of converting an entire flock of shooters from film to crop sensors has now become mired in an endless morass of ill-fated explanations, half-truths and sheer misunderstandings by a new generation buying into the market. The result is a black hole in the ability of some to even make sense of it since the logic of the 'crop factor' has preceded them.


    My thinking is to simply abandon the idea of 'equivalent FOV' altogether. If one buys a crop body and shoots a 28mm, they get used to a certain FOV. They should learn that upping to a full-frame camera will garner a wider FOV with the same 28mm lens (assuming it will cover the sensor). Conversely, one starting out with a full-frame will eventually figure out that a 28mm will give them a 'certain' FOV. But putting that same lens on a crop body will change the FOV. In essence, make the user figure it out.

    Harsh, I know. But since the current state of the situation merely churns out new user after new user walking out of the camera stores with a deer-in-the-headlights looks, there has to be a better system than just tossing out 'equivelant FOV' in the specs.
     
  10. pixmedic

    pixmedic I am the Lord thy Mod Staff Member Supporting Member

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    but, but, but....
    if people did that, then Olympus wouldn't be able to market their new 300mm lens as a 600mm lens.
     
  11. john.margetts

    john.margetts No longer a newbie, moving up!

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    Given the plethora of sensor sizes now in use, it is time to drop identifying lenses with focal length and go for angle of view. Canon already provide this info with each lens (I don't know about other makes) but still insist of focal length as the prime designation.

    For those of us still shooting film, it is worse: 50mm is either 'normal' on full-frame film camera, slightly long on my crop sensor digital, wide angle on my Bronica 6x4.5 and even wider on my Nettar 6x9 folder.

    www.johns-old-cameras.blogspot.co.uk
     

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