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Still confused......but getting there

Discussion in 'Native Lenses' started by woollyback, Dec 17, 2015.

  1. woollyback

    woollyback Mu-43 Top Veteran

    Oct 20, 2015
    Coming from canon I am a bit lost with all the different lens fits. I think......

    A micro four thirds lens fits a M1 no adaptor required

    A four thirds lens fits an M1 but needs an adaptor

    A canon lens could fit an M1 but would need a different adaptor

    Am I right so far?

    So an M1 has a smaller sensor so fov is reduced by 2 or a 50mm lens has a fov equivalent to a 100mm on a Friday sensor?

    Question 1
    Does this also apply toa micr four thirds lens ie a 12-40 will be a 24-80 and not be like a canon efs lens where you get what it says on the lens

    Question 2

    The focal length doubles but the aperture stays the same ie an Olympus 300f2.8 is like a 600 f2.8 but the dof would be deeper due to smaller sensor? So it would be like a 600 f4 or 5.6 fov ff equivalent

    Now the real question no 3

    How do I know what is a micro four thirds nando what is a four thirds is there a naming convention that highlights what is what?? Ie how do I know a 75mm f1.8 does or doesn't need an adaptor

    Thanks for any guidance

  2. kevinparis

    kevinparis Cantankerous Scotsman Subscribing Member

    Feb 12, 2010
    Gent, Belgium
    for Olympus at least, 4/3 lenses are marked Zuiko and micro 4/3 are marked M.Zuiko. Not sure the conventions for Panasonic.. all their 4/3 lenses were marked Leica D. It looks like the letter G signifies a micro 4/3 lens, so either Lumix G or Leica DG

    however go to this page, and you will find lots of information about both platforms

    Four Thirds

    you seem to have your head around the rest of your questions


    Last edited: Dec 17, 2015
  3. MoonMind

    MoonMind Mu-43 Top Veteran Subscribing Member

    Oct 25, 2014
    About focal lengths and FoV: The marked focal lengths on mFT lenses are actual lenghts, not FF equivalents. So a 12-40mm lens for mFT is equivalent to a 24-80mm FF lens, period. In fact, apart from fixed lens compacts, hardly anyone marks or tells equivalent focal lengths on their lenses (though I've found some lenses where they did put it on but added "equiv." - I think I own such a lens, but simply don't remember which on it is; I think it's a third party lens of some sort, but I've got a couple of those ...).

    All in all, getting to the "equivalent focal length/Field of View" on mFT is extremely simple: just double what you read, and you're there.

    Lenses, native or adapted, tell you their actual focal length, so as long as you use a simple adapter, it's just a matter of doubling the focal length to get to the FoV equivalent.

    But if you use focal reducers, things change: They've got a crop factor of less than one, so you need to adjust your maths accordingly. FF lens with 0.71x focal reducer gets you roughly 1.41 (or square root of two) crop factor. I use such a thing to put some of my old (and reasonably bright) Nikon lenses on my mFT bodies - my favourite being the 50mm f/1.4; I get a 35mm f/1.0 this way - or in stricter optical terms, a 70mm f/2.0 equivalent (FoV and DoF) with four times the actual light gathering capability of such a lens ... i.e. a fantastic (street) portrait lens! Once you've wrapped your head around that, it gets reasonably simple and excessively intriguing :) 

  4. Holoholo55

    Holoholo55 Mu-43 Hall of Famer Subscribing Member

    Aug 13, 2014
    Honolulu, HI
    My Zuiko (4/3rds lens) ED 50-200 SWD lens has a prominently marked equivalency label saying 100-400mm. Not sure if all Olympus 4/3rds lenses are marked similarly. It works great on my EM1, BTW, with an MMF-3 adaptor, which preserves the weather-sealing.
    • Informative Informative x 1
  5. Holoholo55

    Holoholo55 Mu-43 Hall of Famer Subscribing Member

    Aug 13, 2014
    Honolulu, HI
    I added some notations below, marked with a [ ]

  6. mcasan

    mcasan Mu-43 All-Pro

    Feb 26, 2014
    Comparing the FOV and aperture between a given M43 lens....to its equivalent in 35mm FF systems....double both the lens length and half its aperture (double the number). See the M43 lens charts at the bottom of this page: Micro Four Thirds system - Wikipedia, the free encyclopedia

    On my Canon bodies I used to use F8 as the default aperture for shooting wildlife. On my E-M1 the default aperture is F4.
  7. PakkyT

    PakkyT Mu-43 Hall of Famer

    Jun 20, 2015
    New England
    People often throw out the "equivalent aperture" theory but I think most of the time people also over simplify it and so it is kind of misleading. First off, when talking about "equivalent aperture" you are talking about depth of field of your photo. When talking about light gathering of the lens, then f/4 is f/4 regardless of what system you are using.

    With aperture, nothing about the sensor size changes the aperture's effect on the photo. The thing that people almost always fail to include is that with a change in sensor size, you get a change in field of view and therefore if you want the same magnification as another sensor size (if you want your subject to fill your frame the same way), for the same focal length lens, you have to change your camera to subject distance. As an example, you use a 35mm camera to shoot a head & shoulder portrait of someone with a 50mm lens. To shoot the same head & shoulders photo on 4/3rds with a 50mm lens to get the same framing you need to step some distance further away from your subject.

    Depth of field is determined by focal length, aperture, and distance (notice sensor size is not there). If you change any single aspect of those three, you change DoF. So in the above example, you are still using the same aperture and the same focal length, but because on 4/3rds you had to step much further away from your subject, THAT is what changes your DoF, not just a change in sensor size. Likewise, you can keep distance and aperture the same but switch your 4/3rds camera to a 25mm lens to get the same framing. But again, you have changed one of the three things (focal length) so your Depth of Field changes.

    Anyway, when speaking of "equivalent aperture" I think it is important to realize that it only applies if you are also applying equivalent magnification of your subject in your frame which means you have changed either focal length or distance as the root cause of your DoF change (when maintaining the same aperture).
    • Informative Informative x 2
    • Like Like x 1
  8. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    My 4/3's ED(or ZD)70-300 has the equivalent 140-600mm label on it too.
  9. woollyback

    woollyback Mu-43 Top Veteran

    Oct 20, 2015
    Awesome thanks folks

    I am on the right track now
  10. EarthQuake

    EarthQuake Mu-43 Top Veteran

    Sep 30, 2013
    What you say is mostly, but not entirely correct. If you keep focal length, aperture, and distance constant, and make sensor size the variable, you certainly do change DOF. You'll end up with different framing for the shot though, so the comparison has little merit. Sensor size is what determines which focal length you need for a given field of view as well, so it's a very important part of the equation. You can't simply remove it and expect to make any sense out of the information, as it's impossible to calculate DOF without knowing the sensor size. DOF is dependent on magnification/output size, which is reliant on sensor size.

    There are also two ways to look at light gathering. You've got light per square mm, in which case f1.8 is f1.8 no matter how large the sensor is, light per square mm is what is used to calculate exposure and is certainly important. The other way is total light, or how much light is recorded by area, larger sensors record more light for a given nominal aperture. More total light means less noise, and if we assume equally efficient sensors (rarely the case, however, the differences are generally not large enough to throw the theory out of whack), a sensor twice the size (M43 vs FF = 4x the total light or a 2 stop difference) will give roughly the same noise performance when used at two ISO stops higher than the smaller sensor, which throws off any point one would make in relation to light per square mm and exposure. With this in mind, if you want to talk about equivalent images between systems, you have to account for focal length, aperture, and sensor size, as all three are elements of the resulting image, and the quality of the image.

    I'm of the opinion that you should either convert all the lens' properties to equivalent or none, or at the very least explicitly state which properties you are converting to avoid confusion, typically I will state for FOV and DOF and ignore the rats nest that is light gathering as discussions typically get out of hand. In reality, a 12-40/2.8 is a 12-40/2.8. It is not equivalent to a 24-80/2.8, however, one can make a very good argument that it is roughly equivalent (in terms of the end result, fov, dof, noise, in other words the actual photograph) to a 24-80/5.6 by basically any metric you could use (again, assuming sensors are equally efficient, in real world use it's a bit more complex).

    Another way to look at it: Let's say for the sake of argument 12-40mm becomes a 24-80mm lens when used on a 2x crop sensor. The physical aperture of the lens (40/2.8 = 14.28mm at 40mm) doesn't magically get bigger, so, to calculate the nominal aperture you would do 80/14.28, which unsurprisingly equals F/5.6. The physical aperture determines both DOF and total light, which determines noise. The 2.8 is 2.8 is 2.8 mantra only applies of you don't convert any of the lens' properties.

    I get that people are sick of the equivalence thing, but really, if we could stop with the partial conversions, others would stop harping on things like equivalent aperture theory.

    TL;DR: DPR wrote an excellent article on the topic with very clear visual examples here: What is equivalence and why should I care?
    Last edited: Dec 19, 2015
  11. PakkyT

    PakkyT Mu-43 Hall of Famer

    Jun 20, 2015
    New England
    No you don't. How would the lens know that you changed the sensor size and change its own properties?

    I clearly stated you get a different framing. But the point was that DoF changes are the result of decisions made to focal length or distance to subject because of the sensor's framing, but not simply because of the sensor itself has any effect on the image projected out the back of the lens. While it may seem like nit picking to you, it is important to understand because some people read the equivalent aperture stuff and mistakenly think the aperture is actually somehow different now because of the sensor and incorrectly start thinking their lens is "slower".
    • Agree Agree x 4
  12. EarthQuake

    EarthQuake Mu-43 Top Veteran

    Sep 30, 2013
    The sensor does not change the optical properties of the lens, this is true, and I never suggested otherwise. However, the optical properties of the lens are not, in fact, the sole determining factor of DOF. DOF is determined by the physical size of the circle of confusion when viewed at a specific physical size and from a specific distance. Magnification and viewing distance are also parameters in DOF, and yes, changing those changes DOF as well. This is why DOF scales on lenses are not accurate for every use, they used fixed assumptions for some of these parameters.

    As such, calculating DOF is dependent on magnification, which is dependent on sensor size. It's impossible to calculate the DOF for 50mm F2.8 at 3m unless you know the sensor size (the portion of the image circle recorded), the magnification (print size or screen size), viewing distance and of course focal length, aperture and distance to subject.

    If you're trying to say that the sensor does not in any way alter the way the lens lets in and bends photons, I agree with you completely. However, this is not DOF, DOF has a very clear and well establish definition and method of calculation.

    I agree that the aperture does not magically change, as stated in my previous post. However, neither does the focal length. A 12-40/2.8 is a 12-40/2.8. It is not a 24-80/2.8 in any way shape or form, referring to it as such is just as much of an inaccurate simplification as you seem to be railing against here.

    It is also very much true that the sensor determines the focal length of the lens you will need for a given framing/FOV. This also means that, if you keep aperture ratio and FOV constant, changing the sensor size most certainly does change the DOF (what's more, if you keep the physical aperture size constant rather than the aperture ratio, the DOF stays the same regardless of sensor size). Whether you want to attribute this to the sensor or lens is a chicken or egg question. I prefer to refer to the total system, because a sensor can't take a photo without a lens, and a lens can't capture an image without a sensor.

    Saying all that, the images I get from my M43rds gear are good enough, exceptional even when considering the size/weight of my kit, which is about half that of the FF gear I used to shoot with, and I am in no way advocating that a certain system is "better", systems are only better for individuals, not better on some absolute level.
    Last edited: Dec 22, 2015
  13. marktegethoff

    marktegethoff Mu-43 Regular

    Dec 4, 2015
    Washington, DC
    Mark Tegethoff
    @PakkyT@PakkyT and @EarthQuake@EarthQuake,

    I think you're both right, and you're both basically saying the same thing, just with slightly different wording. I think point that both of you are essentially making is that lens measurements are lens measurements, and that *equivalencies* are just that, equivalencies (that should be applied consistently or not at all).
    • Agree Agree x 1
  14. PaulGiz

    PaulGiz Mu-43 Veteran

    Jan 3, 2013
    Rhode Island, USA
    For choosing focal lengths, if you're used to FF (or 35mm), then double the focal length to approximate the FOV.

    For everything else, why not just stop thinking in terms of other formats? Once you get used to seeing and thinking M43, you don't need to do equivalencies.
    • Agree Agree x 3
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