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Yet another equivalence question - FF vs M4/3 brightness

Discussion in 'Olympus Cameras' started by nublar, Aug 6, 2015.

  1. nublar

    nublar Mu-43 Regular

    159
    Jan 22, 2013
    SOCAL
    Will two photos taken at the same equivalent aperture at the same shutter speed and iso be any different, with respect to exposure?

    For example:
    25mm f1.4 @ 60s, iso200

    vs.

    50mm f2.8 @ 60s, iso200

    Will these photos be nearly the same brightness? It is my understanding that FF will let you up the ISO with less noise.
     
  2. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Lorenzo
    They will be definitely different. The "equivalent aperture" has nothing to do with exposure, exposure triangle, etc. The "equivalent aperture" is only relevant, with big approximation and assumptions, for noise amount, DoF and diffraction.

    If you want the same brightness you have to use the same ISO, aperture and shutter speed on any camera. If you do you'll get the same brightness and less noise on FF.
     
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  3. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    Yes, subject only to very minor and, for us, ignorable differences in transmission losses between the two lenses. This is why the "T-stop" measurement system was invented. (https://en.wikipedia.org/wiki/F-number)

    Edit: OOPS! I misread the post and thought both were at the same exposure, aperture, shutter, and ISO. The one shot at f2.8 will have one-fourth of the light compared to the f1.4. Refer to the Wikipedia article. Sorry.

    A completely different issue. A sensor collects photons, which are the "signal." A larger sensor will collect more photons but its noise level will not increase proportionately. Hence signal-to-noise ratio (SNR) will be better in the larger device, all other things being equal -- which they never are. But the general rule is correct.

    So your options for the bigger sensor are to have less noise (better SNR) at the same ISO as the hypothetical smaller sensor or to have the same amount of noise by shooting at a higher ISO.
     
  4. Conrad

    Conrad Mu-43 Veteran

    Your examples will differ 2 stops in exposure.

    The "equivalent" exposure you are looking for is f2.8 @ 60s, iso800.
     
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  5. DeeJayK

    DeeJayK Mu-43 Hall of Famer

    Feb 8, 2011
    Pacific Northwest, USA
    Keith
    Gotta love the "equivalence" discussions. So far we've got two replies and two opposing answers. :doh:
     
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  6. Nawty

    Nawty Mu-43 Regular

    83
    May 1, 2015
    Exposure is a factor of shutter speed, aperture and sensitivity (ISO), sensor size has nothing to do with it.

    Edit, focal length can be discounted too as aperture includes that in its value (f/).

    So if you remove the focal length from you exposure examples you can clearly see they are different and so would result in different brightness
     
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  7. tkbslc

    tkbslc Mu-43 Hall of Famer

    Only if you also use equivalent ISO (i.e. 800 on the FF camera).
     
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  8. nstelemark

    nstelemark Mu-43 Hall of Famer

    May 28, 2013
    Halifax, Nova Scotia Canada
    Larry
    One thing to keep in mind is that SNR only starts to matter as your noise floor starts to rise, ie your signal amplification increases (ie ISO).
     
  9. nublar

    nublar Mu-43 Regular

    159
    Jan 22, 2013
    SOCAL
    So, assuming the same SS/ISO, the FF at f2.8 will always be -2EV compared to anything at f1.4 no matter the sensor size (whether it's m4/3, camera phone, 1", etc)?
     
  10. Nawty

    Nawty Mu-43 Regular

    83
    May 1, 2015
    That isn't equivalent ISO. Equivalent ISO is 200, just as equivalent shutter speed is 60s - the apertures have varied in the examples but from and exposure point of view the equivalent of f/1.4 is f/1.4.
     
  11. Nawty

    Nawty Mu-43 Regular

    83
    May 1, 2015
    Correct.
     
  12. tkbslc

    tkbslc Mu-43 Hall of Famer

    It is an "equivalent ISO" because it gives similar noise, just like we say f2.8 is equivalent to f1.4 because it gives similar DOF. You can't change one without the other or you change exposure.

    Using the same shutter speed:

    m43 with ISO 400 and f2 at 25mm
    FF with ISO 1600 and f4 at 50mm

    are going to have just about the same DOF, framing and noise. That's why they are called "equivalent". Pictures should be just about the same.
     
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  13. Nawty

    Nawty Mu-43 Regular

    83
    May 1, 2015
    I don't buy that at all, certainly not where exposure is concerned and certainly not where noise is concerned either, nor dynamic range. The generation of the sensor plays far mor of a role than sensor size and at that point it becomes too complex to generalise as you would have to ask what specific camera models are being discussed too.

    All this talk of equivalence is clearly confusing some people so the less we talk about it the better. The only things equivalence are relevant to are field of view and DoF and even then we are talking about equivalence to another small format, not an ultimate standard.
     
  14. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Lorenzo
    Yes, same exposure/brightness, but the amount of noise will be different.

    The "equivalent aperture" tries to do the opposite: to get the same noise level from different cameras (for the same exposure/brightness) and this means to:
    1. assume that all the sensors, from cellphones to FF, perform the same (and this is technically correct at the pixel level, with a huge same tech assumption)
    2. then you can explain the difference in noise with an (almost imaginary) smaller aperture that let pass less light hence more noise
    3. you have to completely ignore shutter speed and this is why you cannot use this other aperture to compute exposure

    So you end up with two apertures:
    - the real one to be used for exposure
    - the equivalent one only to compare DoF, diffraction and (with big assumptions) noise
    - IMO ugly
     
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  15. MAubrey

    MAubrey Photographer

    Jul 9, 2012
    Bellingham, WA
    Mike Aubrey
    I get really tired of the discussion, but it's nice to see Korenzo knock it out of the park.
     
  16. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    I don't get why this is so hard for people to understand....
     
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  17. nstelemark

    nstelemark Mu-43 Hall of Famer

    May 28, 2013
    Halifax, Nova Scotia Canada
    Larry
    Because the "internets" has invented the concept of "equivalent aperture" and "total light" to explain the somehow hard to grasp concepts of DOF and sensor noise...

    The OPs post is actually the logical outcome of this invention.
     
  18. tkbslc

    tkbslc Mu-43 Hall of Famer

    I also don't get why people seem so threatened by it.
     
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  19. nstelemark

    nstelemark Mu-43 Hall of Famer

    May 28, 2013
    Halifax, Nova Scotia Canada
    Larry
    Yup anyone who feels 4/3 is inferior should have a look at a couple of these shots:

    http://www.photographerslounge.org/threads/35152/

    5MP more than a decade old sensor tech...
     
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  20. tyrphoto

    tyrphoto Mu-43 All-Pro

    May 25, 2014
    Seoul | NYC
    ㅇtㅈyㅅr
    The equivalent aperture has to do with DoF and not light gathering ability. Therefore, the two examples the OP gave, in regards to exposure, they will be different.