Crop Factor on NEX - 6

Discussion in 'Sony Alpha E-Mount Cameras' started by kyngfish, May 4, 2014.

  1. kyngfish

    kyngfish New to TalkEmount

    May 2, 2014

    You guys were great with the last question so I thought I'd ask another. I've been reading about Crop Factor with the APS - C sensor. My last decent camera was a Canon 1N, which at the time I guess was a pro-sumer level 35mm I inherited from my grandfather. I loved shooting things with the 28mm lens which seemed to be his lens of choice as well. I still have the camera and the lens, which I was thinking of adapting to the NEX-6, but because obviously the sensor is smaller, it impacts the field of view for the 28mm.

    My question is, when adapting an older lens that belonged to a film camera, is it as simple as multiplying the crop factor, as in, a 28mm lens is really more like a 45-ish mm, or is it more complex? If I buy a specific e mount 50mm lens or other type of lens, are they engineered for the APS-C and then does that crop factor not apply?

  2. Hawkman

    Hawkman TalkEmount All-Pro

    Sep 10, 2013
    Virginia, USA
    Yes, for the most part it is pretty much that simple. You multiply the crop factor, which for the Sony APS-C sensors is 1.5, by the actual focal length of the lens, like 28mm, to get the "35mm equivalent" focal length of 42mm.

    Also, I understand that you need to multiply the minimum f-stop (largest aperture value) by the same 1.5 crop factor to get an equivalent min. f-stop. So an f/2 lens becomes an equivalent f/3.

    And, actually, that same calculation applies even to lenses designed for APS-C. If the lens' actual FL is 50mm, it has a 35mm-equivalent FL and field of view like that of a 75mm lens on 35mm.
  3. kyngfish

    kyngfish New to TalkEmount

    May 2, 2014
    OK, so if I'm looking for an equivalent for my 28mm f2.8, I need to find a 17mm 1.8 or 2?
  4. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    A 19mm f/2 - you need to calculate from the effective focal length, i.e. 19mm = 100%, 28mm = 150%.

    Closest matches: The Sigma 19mm f/2.8, the Sony 20mm f/2.8 or the Sony Zeiss 24mm f/1.8.
  5. stephen431

    stephen431 TalkEmount Regular

    May 2, 2014
    I was under the impression that only focal length is multiplied 1.5x for FF equivalent while the f-stop is not multiplied as it is roughly the same
  6. jai

    jai TalkEmount Top Veteran

    Feb 4, 2013
    The f-stop is unchanged when considering how much light you will get for an exposure. So with a 28mm F2.8 a shot that would be well exposed at 1/60s on full frame would also be properly exposed at 1/60s on a crop sensor.

    If you are looking purely at depth of field, you could argue that you need to multiply the f-stop by the crop factor as well. So a 28mm f2.8 shot wide open on a crop factor camera will give you a depth of field equivalent to a 42mm at f4.2 on full frame.

    But! That only applies if you are framing the same shot (same composition), with the same lens. So you would need to step back to do that on a crop factor camera.

    So you could also argue the depth of field is the same, it's just that you are changing your distance to subject. Different ways of looking at the same thing.
    • Like Like x 1
  7. jai

    jai TalkEmount Top Veteran

    Feb 4, 2013
    Also, if you really love the lens, and you are not interested in an A7 / A7r camera, you could do what I do and use a speed booster. Your 28mm lens will have the 28mm full frame field of view, and have an effective f stop of F2.0.

    I paid a lot of money for a legit one, but don't regret it (even though I had to cut little bits off my Minolta lenses to get them to work).

    I never use my old rokkors without it anymore. Booster White Paper.pdf
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