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35mm equivalents

Discussion in 'Native Lenses' started by rash_powder, Oct 13, 2011.

  1. rash_powder

    rash_powder Mu-43 Regular

    25
    Oct 10, 2011
    Looking at lenses on the B&H website, I see that the lenses that are native to the m4/3 format give the focal length and then the 35mm equivalent.

    I believe I have a reasonable understanding of the way an adapted 35mm lense will work on the camera - with the crop factor and such it makes a 50mm to appear to work like a 100mm (from the angle of field of view).

    So, why do they list a m4/3 lense as, for example, 14-42mm (28-84mm 35mm equivalent)? Is there a crop factor associated with a native m4/3 lense? Does a 14mm m4/3 not give a 14mm on a 35mm's field of view?

    This has me confused now. I thought the crop factor only applied to adapted lenses.

    Thanx,

    Matt N
     
  2. Promit

    Promit Mu-43 All-Pro

    Jun 6, 2011
    Baltimore, MD
    Promit Roy
    It does not. The focal length listed is the physical focal length of the lens, so the format crop factor (2x in this case) still applies when making a comparison/equivalent.
     
  3. Amin Sabet

    Amin Sabet Administrator

    Apr 10, 2009
    Boston, MA (USA)
    Right, a native 50mm lens and an adapted 50mm lens give the same angle of view as one another when used on a MFT camera.
     
  4. Grinch

    Grinch Mu-43 Top Veteran

    813
    Jan 9, 2011
    Canada
    It's a standard of comparison to 35mm format, hence any lens used on m4/3 is x2 in 35mm format. The new nikon mirrorless camera is x2.7 , so a 50mm for 35mm format becomes a 135mm and if used on m4/3 it is 100mm equivalent. The equivalent is adjusted by the format of the camera it is mounted on. Hope this helps, maybe someone with more experience can explain in more detail.
     
  5. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    Remember though that this is diagonal field of view. 35mm film is a 3:2 aspect ratio whereas Four-Thirds is a 4:3 aspect ratio. This will greatly affect how an image "looks" with the same diagonal Field of View. A Four-Thirds image will look about the same as a 1.7x crop on a 3:2 sensor, but with the extra long ends cut off (a squarer image).
     
  6. rash_powder

    rash_powder Mu-43 Regular

    25
    Oct 10, 2011
    I am really new to all this and trying to make it make sense in my head, so forgive the slowness here.

    So if I was to mount everything onto a tripod and take pics of a static scene, a native m4/3 lens at 50mm would have the same fov as an adapted 25mm lens? The prints would appear the same?

    I think I may be thinking about this too much.....

    I may have to set my 14-42 kit lens to 25 and find my old nikkor 24mm and run test shots.

    Matt
     
  7. 35mm (full-frame) equivalence only really has meaning if you relate to what various focal length lenses on a full-frame camera mean in terms of angle-of-view. If you do want to apply the 2x "crop factor" to a lens to calculate the full-frame equivalent focal length on a m4/3 camera, apply it to the focal length of EVERY lens, be they native or adapted.
     
  8. photoSmart42

    photoSmart42 Mu-43 Top Veteran

    628
    Feb 12, 2010
    San Diego, CA
    No, a native m43 lens at 50mm would have the same FOV as an adapted 50mm lens if you put both on your m43 camera. It's a relative comparison with a FF sensor. A native m43 lens at 25mm would have the same-ish FOV as a native 50mm lens on a FF camera (if you shoot in 3:2 mode on both). The lenses are the same (focal length is a lens characteristics, not a sensor characteristic), what matters is the size of the sensor behind them.
     
  9. Luke

    Luke Mu-43 Hall of Famer

    Jul 30, 2010
    Milwaukee, WI
    Luke
    Totally ignore the "equivalence".

    A native 25mm is the same as an adapted 25mm. The measurement system has not changed.

    The discussion of equivalents is to help people visualize the FOV if they are coming from working with film (or full frame cameras).

    A 25mm lens (whether native or adapted) will have the same fov as a 50mm lens when mounted to a FULL FRAME camera.

    I hope that clear it up for you. (and I hope I got it right)

    Looks like I'm a little late to helping out here, but it can never hurt the learning process to read it a few too many times....LOL.
     
  10. Hikari

    Hikari Mu-43 All-Pro

    Nov 26, 2010
    Angle of view has two basic variables, focal length and format size. If those two things stay the same, then nothing changes. If one of those changes, then the angle of view will change.
     
  11. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    The Field of View would be the same as a 50mm lens, but the prints would NOT appear the same. That is why I say that "diagonal" Field of View is misleading when it doesn't take into account differences in aspect ratio. I will give you a visual example...

    Here is a Full Frame image, with crops shown for Canon APS-C (1.6x crop), and Four-Thirds (2x crop):
    sensor-size_comparison.

    Here is what the image will look like from an APS-C sensor using the same lens at the same distance:
    sensor-size_aps-c.

    Here is what the image will look like from a Four-Thirds sensor using the same lens from the same distance:
    sensor-size_four-thirds.

    As you can see, both APS-C and Four-Thirds images look nearly identical except that the APS-C image is WIDER with more of the legs showing. That is due to the difference in width, although the height is nearly identical. Yet, the crop factor on one is 1.6x while the crop factor on the other is 2x, and they have different diagonal field of views (as a technical term). So no, the images are NOT equivalent even if the FOV is. I think "perspective" is also a poor term to describe diagonal FOV. The "perspective" of the two above images look the same, don't they?

    The APS-C image is literally a 1.6x crop of the Full Frame image because they share the same aspect ratio. To say that a 25mm lens on an APS-C sensor will yield the same perspective as a 40mm lens on 35mm film would be correct. However, to say that a 25mm lens will yield the same image as a 50mm lens on a Four-Thirds sensor is simply not correct.

    It's better to think of the Four-Thirds image as an equivalent 1.7x crop that's squarer. ie, a 25mm lens on Four-Thirds would be more equivalent to a 42mm lens on a 35mm film camera, but squarer.
     
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  12. shnitz

    shnitz Mu-43 Top Veteran

    989
    Aug 25, 2011
    Austin, TX
    No, that is not quite how it works.

    In your first post, you ask why they talk about "equivalent" focal lengths, even for native lenses. This is so that those that are familiar with photography know what they're getting with a particular lens. Look here for a quick idea of angle of view:
    Angle of view - Wikipedia, the free encyclopedia
    Those are the focal lengths for classic 35mm film. Now, imagine that I want to buy a new camera. I look at these cameras:
    -Canon 5D with a 50mm lens
    -Nikon D7000 with a 35mm lens
    -micro 4/3 camera with a 25mm lens
    -Nikon 1 with 18mm lens

    Given that these cameras all have differently sized sensors, they will all need different focal length lenses to get the same photo. The above cameras all have a lens that will give a near-identical picture! As you can see, it could be quite confusing if manufacturers only stated the actual focal length, because one would have to learn the individual system to know what they're getting. So, the camera makers all use the 35mm standard of providing an equivalent focal length. This way, if I come to micro 4/3, having no experience in it but knowing a bit about photography, and Best Buy wants to sell me a 14-42mm lens, I know that they are selling me a midrange zoom lens, because they tell me that the equivalent 35mm focal length is actually 28-84, which is a decent range for general photography. Otherwise, if you went to someone with photography experience and told them that they were buying a 14-42mm lens, they would assume that you're trying to sell them an extreme wide angle lens, meant for mainly architecture and landscapes.


    The "effective" focal length comes about because the sensors are all differently sized. A 25mm lens provides a 25mm focal length, regardless of what camera is behind it. However, if you have a micro 4/3 sensor, that is 1/4 the size of the full frame sensor, you can build a lens that is only 1/4 the size. If you were to put a micro 4/3 lens on a 35mm camera, you'd have a tiny round image in the middle of the film, with lots of black space around the edges.


    So, if you don't have any experience with "classic" photography, then ignore the equivalent focal length. A 25mm lens on your camera is 25mm, irrespective of the system that it was originally made for. The only thing is, that 25mm lens made for a Nikon camera has to be much bigger than a lens that was made for a small-sensor camera.

    Equivalent focal length just tells you that a 50mm lens on your camera gives the same perspective as a 100mm lens on a "normal" camera. There is no cropping or anything going on; this perspective shift is only coming about because of the differences in sensor sizes. See if these links help you visualize it:
    Equivalent Focal Length and Field of View
    35 mm equivalent focal length - Wikipedia, the free encyclopedia
    The Panorama Factory -- What is "35mm equivalent focal length?"