mu43 vs APS-C aperture

Discussion in 'Open Discussion' started by GreinerStudio, Feb 16, 2017.

  1. GreinerStudio

    GreinerStudio Mu-43 Regular

    Feb 15, 2017
    I understand the difference in crop factor (2x vs 1.5x) but did not realize there was also a difference in DOF at the same aperture. This leads me to ask...

    Is this purely a DOF phenomenon, or is the light gather of a mu43 at 2.8 similar to a APS-C at 1.8 and therefore as "Fast"?? I'm guessing not, but was not sure as I'm new to the system and coming from APS-C. I imagine it is just a DOF change, but why?
  2. skellington

    skellington Mu-43 Veteran Subscribing Member

    Mar 4, 2013
    Atlanta, GA
    There is a DOF change at equivalent field of view.

    A 25mm lens has identical DoF on every sensor size, at a given distance.(**) And a 25mm lens has a greater DoF than a 35 or 50mm (for APS-C or Full Frame) at a given distance.

    However, all other parameters are basically the same. ISO 200 @ F2.8 @ 1/160 will produce an identical exposure on a m43 as an APS-C or full-frame camera.

    Because the pixels on m43 tend to be smaller than APS-C or full-frame, you'll tend to get some more noise at the higher ISOs. However, the E-M1m2 appears to perform about as well as your Pentax did based on DXOmark scores.

    (**) DOF calculations include a tiny factor based on pixel size and size of final output. This makes DOF on a smaller sensor a tiny bit different. But this depends on your output format and is almost a rounding error.
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  3. greenboy

    greenboy Mu-43 Top Veteran

    Light gathering is as fast, only DOF is different as is related to crop factor. As a newcomer to photography a couple years back I was astounded how many supposedly knowledgeable photographers on APS-C or FF would try to dump on MFT using disinfo about this.
    Last edited: Feb 16, 2017
  4. Adam CL

    Adam CL Mu-43 Regular

    Feb 16, 2017
    The change in DOF is only because you'll use wider lenses than you would have on FF. In other words, a 20/1.7 on FF and m43 will produce the same DOF, but on the m43 you'll have a field of view roughly equal to that of a 40mm lens on the FF camera - and a 40/1.7 on FF would produce shallower DOF.
    Last edited: Feb 16, 2017
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  5. PakkyT

    PakkyT Mu-43 All-Pro

    Jun 20, 2015
    New England
    To expand a bit on what Adam just said, DoF is determined by Focal Length, aperture, and distance from camera to subject. Change any of those three things and your DoF changes.

    A lot of sites don't always explicitly state WHY the DoF changes when you go to a micro-4/3rds sensor camera from a full frame camera or an APS sensor camera. It isn't the sensor size at all. Instead because the crop factor changes your field of view changes. Therefore to get the same magnification (how your subject fills the frame) when you switch crop factor is that you have to change either the focal length being used or the distance to your subject. THOSE are actually what change the DoF, not the sensor.

    If you took an Olympus OM film camera with an old OM lens mounted on it, put it on a tripod, took your photo, then removed the OM camera and instead placing an OM-D camera behind that same lens not changing the distance (tripod stays put) nor changing the aperture of that lens, the resulting photo would have identical DoF as the film camera. What would look different about the shots is the OM-D version would have a much smaller field of views (if your film shot was a head & shoulders shot, your OM-D shot would now be a lips & nose shot ;) ). In the real world, with the OM-D you would need to move the tripod back further to frame the shot the same or leave the tripod put and switch to a wider focal length.
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  6. SojiOkita

    SojiOkita Mu-43 All-Pro

    Feb 23, 2014
    Not exactly.
    You have to take into account the fact that a m43 image has to be magnified twice more.
    So, when looking images of same size (on screen or prints), the dof of a m43 picture with a 20 mm f/1.7 will be twice less than the one of a 24x36 picture with a 20 mm f/1.7.
    (Considering that the focus distance is the same.)
    In reality, that will be very difficult to assess because the produced images will be very different (because of the different the field of view)

    Comparing a m43 @ 20 mm and a 24x36 @ 40 mm is a lot easier because the image will be similar.
    At the same aperture number, for example f/1.7 (which means that the diaphragm opening diameter is in fact twice larger on the 24x36), and the same focus distance, the DOF will be twice larger on the m43 picture.
    Light gathering will be the same though (four times more light on the 24x36, for a sensor surface four times larger).

    DOF is linked to the square value of the focal length (F * F), the aperture number (which is the same) and circle of confusion. (F^2 / N / C)
    Of course the circle of confusion is something quite theoretical, but we can consider that it is twice lower on m43 (that is what most dof calculator consider).

    With the same magnification, DOF would be four times higher on m43 compared to 24x36, but considering the higher magnification, that makes it only twice higher.

    In conclusion:
    - light gatering depends only on aperture number, not focal length nor sensor size.
    - for depth of field, you can consider the same ratio as the crop factor. Comparing a 2x crop factor camera to a 1.5x crop factor camera makes a 1.33 ratio in terms of depth of field.

    Some thing to keep in mind: this is theoretical, formulas used consider "perfect" lenses, and real world lenses are not perfect.
  7. Adam CL

    Adam CL Mu-43 Regular

    Feb 16, 2017
    I'm not quite sure I'm following you, but what I meant is that if you took a picture with FF @ 20/1.7 and cropped it to the equivalence of m43 FOV, and then took the same picture (distance, settings) with m43 @ 20/1.7 the resulting images would be the same. The differences would be DR and SN. Am I misunderstanding your post?
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  8. Ulfric M Douglas

    Ulfric M Douglas Mu-43 Hall of Famer

    Mar 6, 2010
    One of the beauties of m4/3rds is the short mount : meaning you can fit a LOT of lenses, including APS and 35mm, on your m4/3rds bodies with the right cheapo adapters.
    This means you do not need to imagine, you can actually mount your favourite APS lenses on a m4/3rds body and find out for real what the difference in framing really means.
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  9. SojiOkita

    SojiOkita Mu-43 All-Pro

    Feb 23, 2014
    There was no mention of cropping in your post, so I was talking about comparing an non cropped 24x36 image @ 20/1.7 and a non cropped m43 image @ 20/1.7.

    Of course, if you crop the 24x36 image, then I fully agree with you ;)
    You are then comparing two images with the same focal length, the same aperture, and the same magnification.
  10. Adam CL

    Adam CL Mu-43 Regular

    Feb 16, 2017
    The gist of my argument is that a 20/1.7 is a 20/1.7 on both FF and m43, regardless of physical crop (m43) or crop in PP (FF). Even if you don't crop the FF picture, the DOF will still be the same (but the FOV different). In other words, sensor size doesn't affect DOF, only FOV.

    Frankly, I don't understand why crop factor is relevant. People have been using medium, large and half format for a long time without worrying about equivalence. Just a few years ago, when APS-C was almost standard among hobby photographers, hardly anyone talked about crop equivalence and even less about DOF equivalence.
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  11. greenboy

    greenboy Mu-43 Top Veteran

    Nothing is relevant; all is folly.
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  12. TheMenWhoDrawSheeps

    TheMenWhoDrawSheeps Mu-43 Veteran

    Jun 15, 2016
    The same reason why FF gives less DOF vs APS-C at the same f-stop.
    As many stated it´s focal length vs aperture vs distance. Very True, but so dull - let´s get philosophical.) The problem is it´s math consistancy vs reality.
    What would you rather choose - knowing that under same conditions on different sensor sized cameras you should take same or almost same Aperture, ISO and Shutter speed applying crop only to the focal length, but getting different results in terms of dof, and noise.
    or Getting the same image in terms of FOW, DOF, and even NOISE(with same technology lvl of course), but you have to apply your 2stops crop factor to Focal length, Aperture and ISO(2 stops means 4 x iso) keeping same shutter speed.
    1.5x crop is 1 stop of light, 2x is 2 stops - put it whichever way it comforts you. Manufacturers went for mathematical consistancy, not the real world application.
  13. tkbslc

    tkbslc Mu-43 Legend

    The actual aperture size is a function of focal length divided by aperture. Since the crop factor of m4/3 requries that you use smaller focal lengths for the same framing, you end up with a smaller resulting aperture size.
    For example:

    FF: 50mm f1.8 = 50/1.8 = ~28mm aperture
    4/3: 25mm f1.8 = 25/1.8 = ~14mm aperture.

    When using equivalent focal lengths, we've equalized everything about the DOF and BG blur equation, except for aperture size. And in this case, that means that since FF has twice the aperture diameter, it will have half the DOF and twice the bg blur.

    So short version is that m4/3 has deeper DOF and less bg blur because it will always have a much smaller aperture diameter with all things equal.
  14. tkbslc

    tkbslc Mu-43 Legend

    You didn't spend much time on the Canon forums, then! It is one of the few systems with multiple sensor sizes (1.6x, 1.3x, and FF) in the same lens mount. There were major debates about equivalency and DOF/Noise advantages from the beginning!
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  15. bikerhiker

    bikerhiker Mu-43 All-Pro

    Dec 24, 2013
    Crop factor determines the angle of view of the lens. Obviously, if you need to maintain the same angle of view of both crop factor (2x vs 1.5x), you can not have identical shooting distances with both crop factors if you want to maintain the same field of view and hence the DOF changes between these crop factors. BUT, if you maintain the SAME shooting distance, then you will have the same DOF, albeit one photo will be cropped 2x and the other @ 1.5x.
    For example, if you shoot full frame at a set distance and then you decide to crop 1.5x or 2.0x, the actual DOF will not change just because you crop the images digitally. What it will change is that, the crop removed the edges that giving you an illusion that you are gaining more DOF.

    Focal length has no relationship to DOF, because the focal length value is determined by the lens being focused only at infinity. Which is why DOF is governed by aperture, angle of view or field of view and shooting distance.
  16. tkbslc

    tkbslc Mu-43 Legend

    Every DOF equation you can find will have focal length as an input.
  17. bikerhiker

    bikerhiker Mu-43 All-Pro

    Dec 24, 2013
    Yes.. For convenience, because of the crop factor. People can associate focal length because it's printed on the lens. Angle of view is not printed on the lens. But focal length is NOT what determines DOF. Angle of View is. 2 different things. 2 lenses made by 2 different makers that have the same focal lengths can have differing angle of view. This is illustrated between the Panasonic 25mm f/1.4 and the Olympus 25mm f/1.8 where one is actually slighter wider in angle of view as opposed to the other. Another example also would be the Nikkor 70-200 VR2 and the Nikkor 70-300 VR where at 200mm, one is also slightly wider than the other as well.
  18. Costas_Gr

    Costas_Gr Mu-43 Regular

    Oct 3, 2016
    Perhaps will help a simple example. If I'm wrong emend:
    At a scenario where we want to shoot two our friends, indoor low light with a lens 20mm mft = 40mm FF, mft lens at f2.8 can have two persons all in focus, while the Foul Frame which will need f5.6 for the same DOF.
    This helps mft cameras (as it is known they have noise problem at hight ISO) to keep lower ISO and the quality of the shot to be close to FF camera.
    I have do this test with an aps-c Nikon D7200. I was with sigma 30mm f1.4 and my friend with Nikon 50mm f1.8
    Of course his lens has bigger focal length (sigma 30mm =60mm in FF, Nikon 50mm = 75mm in FF) for that I let him to shoot more back than me. With Sigma at f2.8 I had the 2 person in focus. One all in focus and the second acceptable. Nikon, lost at all the second person.
  19. EarthQuake

    EarthQuake Mu-43 Top Veteran

    Sep 30, 2013
    A combination of sensor size, lens focal length, physical aperture opening (or f-stop which is ratio of FL to aperture opening), distance from camera to subject, and magnification/print size determine DOF and background blur. If you change any of these variables (yes, even magnification) you change DOF as it is classically defined.

    AOV is (not unlike the f-ratio) simply a calculation you can make when you know other fixed, physical variables. Specifically, focal length and sensor size.

    The variance examples you give are due to two things:
    1. The focal length for some lenses changes from MFD to infinity, this is due to the lens elements moving around and the focal length physically changing, common with zooms but also true for lenses with very long focus throw like macro lenses.
    2. Focal lengths are rounded to the nearest common increment. The 70-200mm may only be ~170mm at the long end in reality.

    When you see variances in the above two, the AOV varies as well. Angle of view is intrinsically tied to focal length, these are not the same thing but they are absolutely tied together. For instance, you can't have a 12/2 on an EM1 that has an 84° AOV and a 12/4 on an EM1 that has a 64° unless the focal length listed on the 12/4 is wildly inaccurate.

    Angle of view does not exist on its own, you need to know the sensor size to know the AOV. Focal length on the other hand is absolute and can be physically measured, and does not vary when you use the same lens on difference sensor sizes.

    Now, back to the original question, if it hasn't been answered sufficiently yet:

    In no uncertain terms, the difference in DOF for the same AOV and same distance to subject between M43 and APS-C is about 2/3 stops, it's ~0.6 vs Canon and ~0.7 vs Nikon/Sony/everyone else who use slightly larger APS-C sensors than Canon.

    This means that a 25mm 2.0 on M43 will produce roughly the same DOF as a 35mm 2.5 on APS-C. Or a 42mm 1.4 will produce the same DOF as a 56mm 1.8.

    There are also two ways to look at light gathering (per area which determines noise/total light and per unit (ie mm²) which determines exposure), but people tend to get quite upset when this is brought up so I will say no more.
    Last edited: Feb 16, 2017
  20. bikerhiker

    bikerhiker Mu-43 All-Pro

    Dec 24, 2013
    "In no uncertain terms, the difference in DOF for the same AOV and same distance to subject between M43 and APS-C is about 2/3 stops, it's ~0.6 vs Canon and ~0.7 vs Nikon/Sony/everyone else who use slightly larger APS-C sensors than Canon."

    Can you clarify how can you have the same Angle Of View shot at the same distance to subject with M43 and APS-C when the crop factor is different? Are you basing this on 2 different focal lengths?
    Last edited: Feb 16, 2017
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