u43 crop factor - is it really 2 ?

Discussion in 'Native Lenses' started by pdk42, May 1, 2013.

  1. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    We all know that the MFT "crop factor" is 2 don't we? Well, take a look at this post by Ned:


    I think this shows pretty well that whilst MFT may be notably narrower than APS-C, it's actually quite close in height (actually 13mm compared to 14.8mm)

    Inspired (!) by this, I did a quick bit of maths on what the crop factor would be if we kept the height of the MFT sensor but extended the width to match APS-C.

    The answer is 1.68

    Now, I don't know about you, but one of the things I like about MFT is the 4:3 aspect ratio. I find the 3:2 of FF a bit 'oblong' and in any case I often crop my images to square. Given this, the extra width of APS-C (or FF) is somewhat irrelevant and I can get a closer approximation to an FF focal length if I use something closer to 1.7 than 2.

    Anyhow - hardly a profound conclusion, but interesting anyhow. Of course, as Ned points out, it's better to forget about crop factors entirely and just learn the FL/view relationship on MFT - but for old 35mm film users, it's still a helpful crutch.
  2. kponds

    kponds Mu-43 Regular

    Mar 18, 2013

    It actually feels like its more than 2x to me. I often judge the width of the angle in horizontal terms. With my 25mm, it feels like it's a little bit more narrow than my 50mm on FF.

    But I usually end up cropping less on 4:3 than on 3:2 for my typical output formats (8x10, 11x14, and 16x20), so objectively it would be less.
  3. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Real Name:
    I crop to 3:2 fairly often (print 12x18, or display at 1920x1280). Makes for a crop factor of 2.08 which isn't too bad. Wouldn't say no to a multiaspect sensor though (maintaining a 2x crop for 16:9 and 3:2).
  4. silversx80

    silversx80 Mu-43 Veteran

    Apr 27, 2012
    North Carolina
    There is no crop factor :wink:. The :43: lenses are designed for the :43: sensor size, and none larger.
  5. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Another one of "those" debates, the ones that are impossible to resolve to everyone's satisfaction.

    Crop factor is usually based on the diagonal of the frame, not the height and not the width. The problem here arises because the proportions of the frame are different. If the proportions were maintained it would not matter whether height, width, or diagonal were used because the crop factor would be the same for all 3 dimensions.

    So, what does diagonal have going for it that height and width don't, and what makes diagonal a better option for the calculation than either of the other 2 dimensions?

    Simple: It defines the diameter of the image circle. You can rotate the camera and have your rectangular frame in portrait orientation, landscape orientation, or anywhere in between. If you want to use either the height or width of the sensor to determine crop factor you run into problems because it would mean that when comparing different formats you would always have to compare them in the same orientation but it doesn't necessarily follow that one would always choose to use 2 cameras with differently proportioned sensors in the same orientation. You may, for example, choose to frame a particular scene in portrait orientation with a 4:3 sensor and in landscape orientation with a 3:2 sensor, simply because of the difference in proportion and the effect that has on what is included and excluded in each case.

    The diameter of the image circle is constant regardless of how you orient the frame, whereas the height and width of the frame change—they swap—as you move from landscape to portrait orientation. If you're going to compare 2 things with different aspects, it does help to compare them on a specification that doesn't alter at the whim of the user and sensor diagonal/image circle diameter is the specification that doesn't change.

    So my vote is for sensor diagonal. It's independent of the proportions of height and width, and it also just happens to define the image circle which is the important dimension for the lens designer. The lens designer doesn't care how high, or how wide, the sensor is, they have to ensure that the image circle covers the corners of the sensor, and the diagonal is what is critical in ensuring that they succeed in doing that.
  6. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    Doing it the other way - shrinking the width of FF such that the height remains at 24mm, but the width reduces (to 32mm) to make a 4:3 aspect ratio - gives a crop factor to MFT of 1.84. On reflection, I think this is probably a better comparison since it represent what would happen if if you were to crop the FF image to match the MFT one.
  7. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL
    IMHO, that is the wrong answer.

    If you specify a crop factor without specifying some special cropping of one or the other formats to match the aspect ratios in the same phrase then you should only spec the crop factor for the diagonal in the native aspect ratios of both formats. Stating that "the crop factor is X" with no qualifying factors should only be used when referencing the diagonal coverage of uncropped formats.

    That said, the "horizontal crop factor" and the "vertical crop factor" are different when comparing a 4:3 format (m43, virtually all smaller formats, & most of the larger than 35mmFF formats) with any of the 3:2 formats (35mmFF, APS-C film, the myriad of APS-C-esque digital formats) than the conventional "diagonal crop factor".
  8. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    I don't find the "extra width" irrelevant. I try not to crop with any camera I use regardless of format. Back in the film only days I printed full negative and I have again decided to shoot sans cropping in post.

  9. MAubrey

    MAubrey Photographer

    Jul 9, 2012
    Bellingham, WA
    Real Name:
    Mike Aubrey
    That's true, but when you crop 3:2 to 4:3 or crop 4:3 to 3:2, you change the diagonal. And if you want to talk about "equivalent images" you have to cropped something somewhere.
  10. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    What you're shooting also makes a big difference. For instance, if you're doing something like portraits, animals, objects, or other shots which have a definite subject then the height-only crop factor of 1.7x (I've never actually calculated it like pdk42 has and always just used 1.7x as what it looks like to my eye. Great to hear I was so close) is pretty much what you need as that will define the apparent perspective of your subject and that's normally the difference we're trying to put our thumb on between formats. If you're doing something which encompasses scenery and background instead (ie, like landscape), then the diagonal measurement will have more impact to you.

    But the very fact that I started with an "it all depends" statement is all the more reason why we should just throw that measurement out the door. lol.
  11. arad85

    arad85 Mu-43 Veteran

    Aug 16, 2012
    I wrote this the other day:

  12. spatulaboy

    spatulaboy I'm not really here

    Jul 13, 2011
    North Carolina
    Real Name:
    It's offical: The m4/3 crop factor is 2ish.
  13. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    That's true also but if you don't base things on a single standard as a reference you just get confusion,

    And to confuse things even further, let's say you crop a 4:3 image to 3:2, but your full 4:3 frame is a little too wide so you crop at the sides while retaining the 3:2 format. Now your crop factor is different again than what you get when you retain full frame width but just crop the height to get your 3:2.

    Every time we crop an image in some way or another we change the crop factor so tell me what I should regard as a crop factor when comparing my Olympus 75mm to other formats. I wanted 2 things I couldn't get together, a fast lens and a long lens for bird photography. The 75 gave me the speed I needed for shooting in late afternoon in shadowed areas but it isn't long enough for what I want so I crop, often to a quarter or a ninth of the frame (to a half or third of the height or width of the frame). That means I'm cropping to what would be the field of view of an m43 150 to 225mm lens. So, using the diagonal because that's the "official" ratio, is my crop factor 2, or is it 4 or 6 because of how I'm actually using it?

    And that's where the real problem lies. People use crop factor for reference purposes and for comparison purposes, and references need to be standardised. That means we need a single crop factor, not a choice of 3, and that means that we need to select one and only one sensor dimension for calculation of the crop factor. Which one do we choose, height, width or diagonal? None of them is perfect and good arguments can be made for each.

    I'll only make one other point. At present the "standard" dimension is the diagonal and it has been in use for some time for comparison of a number of formats. It is used in lots of published material. Change it and the confusion we have already will get worse, because all future published material from lens manufacturers, camera manufacturers, reviewers and the like will start quoting a new factor and all of the old material is still available on line and in publications, and people start to read conflicting statements, often from the same source but just published at different times. I think that would actually make things worse. Changing existing practice is not something to be undertaken lightly, and if you're going to change it for m43 you would also need to change it for every other format as well because you don't want your crop factor calculated one way for m43 (say height as suggested by the OP) and another way, say width, for APSC.

    I think diagonal is pretty much locked in unless the camera and lens manufacturers can jointly agree on a new standard and I think that's unlikely.
  14. arad85

    arad85 Mu-43 Veteran

    Aug 16, 2012
    When you crop in post, you are effectively changing sensor size, so your crop factor is 4 or 6, depending on your crop. It is the crop size that is giving you the effective focal length changes and the effective sensor size enables you to predict the DoF achievable too (but that is a separate - and often pretty emotive - discussion :wink: )

    Confusion = marketing opportunities :rolleyes:
  15. fredlong

    fredlong Just this guy...

    Apr 18, 2011
    Massachusetts USA
    Real Name:
    I liked 6x7 medium format, so the crop factor is 4. Sometimes 6x6, so the crop factor is closer to 3.something or other. I used 4x5 cameras to. I don't even want to think what that makes the crop factor.

    The funny thing is, when I shot 35mm film I never thought about a crop factor compared to medium or large format. The only thing that concerned me was if the negative was big enough for the intended purpose. For me, u4/3 suits my needs.

    Every format has its own "standard" focal length. Everything wider and longer can be compared to that, not another format.

  16. gcogger

    gcogger Mu-43 Veteran

    May 25, 2010
    Real Name:
    I'm surprised by how much discussion this has generated. If you care about the 'crop factor', then it's very simple, as above.
    - If you want a 3:2 (or wider) image the crop factor is 2.081
    - If you want a 4:3 (or 'squarer') image the crop factor is 1.846

    I'm not sure what else there is to add?
  17. entropicremnants

    entropicremnants Mu-43 All-Pro

    Jul 16, 2012
    Real Name:
    John Griggs
    I'm not sure why any of this matters. The crop I use depends on the material and "crop factor" isn't something I think about when I'm shooting.

    It is what it is and if you get your photos, it's important why, lol?
  18. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    For me what matters is to fill the frame. period

    The frame doesn't matter, what's inside does.
  19. skellington

    skellington Mu-43 Regular

    Mar 4, 2013
    Atlanta, GA
    Real Name:
    You could look at the sensor areas:

    35mm is 864 mm^2.
    APS-C is 368 mm^2.
    APS-Canon is 328 mm^2.
    m43 is 225mm^2.

    Square root of (864/225) = 1.96

    For Full Frame to APS-C, we've got 1.53 or 1.62.

    For APS-C/APS-Canon to m43, we've got 1.28 or 1.20.
  20. Iansky

    Iansky Mu-43 All-Pro

    Dec 26, 2009
    The Cotswolds, UK
    I agree 100% with Gary, like Gary I am also an ex PJ who cut his teeth using analog from 35mm up to and including 10x8.

    Like the ever returning discussion on cameras, I try to maximise what I have with me at the time and not waste frame space.

    I am not bothered about comparing sensor size/crop factors as they are irrelevant for what I shoot as my photography is now a hobby no longer a profession.

    I must add though, the quality of image I am getting from my OMD equates to that from my X100 and in some cases matches that from my D700 (since departed) so that is good enough for me; I have also seen some incredible large prints produced by a brilliant photographer who only shoots with the OMD and has let all his full frame kit go - link to some of his work is here so in his case, crop factor is irrelevant:

    Showcase — Damian McGillicuddy