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another equivalency question

Discussion in 'Open Discussion' started by krugorg, Oct 31, 2013.

  1. krugorg

    krugorg Mu-43 Hall of Famer

    Jul 18, 2011
    Minnesota USA
    If you had a full frame camera with a f2.8 lens and then a crop sensor at f2.8 also, shooting the same scene,... would you end up with, roughly, the same shutter speed if both were exposed the same?

    I think the answer is yes, but a post on an unnamed, inferior photography web site seemed to claim that the full frame sensor would gather more light, which would mean that it would have a higher shutter speed on a given shot versus a crop sensor, when both used the same f2.8 lens, for example.
     
  2. wjiang

    wjiang Mu-43 Hall of Famer

    That sounds like the Stylus 1 review :p It's just the difference between fewer total photons and fewer photons per sensor area. Only the last matters for exposure. There's also a slightly separate factor of photons per photodiode, which will affect things like noise.
     
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  3. dwig

    dwig Mu-43 Top Veteran

    621
    Jun 26, 2010
    Key West FL
    If they are shot at the same T/stop and the sensor system is set to the same ISO (correcting for any differences in two manufacturers' opinion of how to spec the ISO) then matching shutter speeds would yield matching exposures.

    You will find differences is light grasp between radically different lenses with matching f/stops. These differences are usually modest. Cine lenses are often marked in T/stops (Transmission stops) which reflect these differences. These differences between f/stops and T/stops have absolutely nothing to do with the image format (sensor or film size). Usually the difference between a lens' f/stop and its T/stop is in the 0-2/3 stop range.

    There are also differing opinions on how to rate a sensor's ISO. If you check out the DxO test you'll see how the same marked ISO can be up to 1 stop different between two different cameras from two different manufacturers.
     
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  4. RnR

    RnR Mu-43 All-Pro

    Sep 25, 2011
    Brisbane, Australia
    Hasse
    One way to make the web site claim correct is to shoot both camera's for the same effective noise profile in the resultant images. The full frame sensor would gather 4 times as much light as a x2 crop sensor, which could result in being able to use an ISO level 2 stops higher than the x2 cropped sensor. Everything else being equal, including exposure and noise behaviour of the sensors, that would give the full frame sensor a shutter speed 4 times faster than the x2 crop sensor.

    The new retro styled Nikon is rumoured to have a 16MP full frame sensor. It should be a lowlight monster and will probably get close to the napkin calculations above.
     
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  5. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    Arrrrrrrrrrrgggggggghhhhhhhhh!!!

    this will go for 15 pages..... but anyway.

    per square mm (or inch for those metrically challenged) the light hitting the sensor will be the same, so the exposure will be the same. 2.8 is 2.8 is 2.8.

    Overall the larger sensor will collect more light due to the bigger surface area. This "may" affect some things but NOT exposure. The above mentioned criteria that the lenses have the same T stop is neccessary.

    Gordon
     
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  6. RnR

    RnR Mu-43 All-Pro

    Sep 25, 2011
    Brisbane, Australia
    Hasse
    Nah - you jinxed this thread by predicting its length on page 1 :frown:

    Now we have to wait 3 months before someone else can try again...
     
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  7. demiro

    demiro Mu-43 Hall of Famer

    Nov 7, 2010
    I think I grasp this, but I go adrift when trying to figure out background blur. 85/1.8 on FF vs 50/1.4 on APS-C (1.6x crop) vs 45/1.8 (2x crop) on m4/3s vs Sony RX10's 1" sensor at 33/2.8 (2.7x crop).

    What I know is that I'm good shooting portraits with any of the first three. The m4/3s option does not blow the background up as much as the larger sensor cameras, but good enough for me.

    Where does the RX10 fit in though? I did some questionable math and figure it will look something like the 45mm shot with aperture of 3.5 or 4. Is that remotely believable?
     
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  8. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    Equivalence is only for the "look" of an image compared to a base unit. For good, bad or otherwise we've chosen 35mm as that base unit. A 1 inch sensor with a 33mm f2.8 has a 35mm look of 89mm f7.5. A 4/3 lens would be a 45mm f3.8 would give about the same look. Assuming all sensors are equally perfect of course.

    So yes, your maths is good.

    Gordon
     
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  9. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    I agree with Gordon, but in an attempt to stop this reaching 15 pages (by making a contribution to it!), let me try to simplify:

    - Sensor size will not affect the f-stop and shutter speed exposure settings at a given ISO (unless we get into largely insignificant, second order, non-ideal issues such ISO calibration, lens transmission etc. Nearly all of us can ignore these).

    - Sensor size will affect the field of view and depth of field for a given lens's focal length and f-stop (larger sensor = wider field of view and narrower depth of field). However, unless you shoot lots of systems and need to make constant comparisons between them, it's best just to accept what your system does and use it.

    Hope this illuminates and doesn't confuse!
     
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  10. demiro

    demiro Mu-43 Hall of Famer

    Nov 7, 2010
    Thanks Gordon, though I am a bit shocked to hear that my math was correct. Blind squirrel theory being proven, no doubt.
     
  11. krugorg

    krugorg Mu-43 Hall of Famer

    Jul 18, 2011
    Minnesota USA
    Thanks for the info guys!

    It makes a lot more sense now (I think anyway).... all things equal, on the same scene, shutter speed would be the same. If you take into account noise, allowing you to bump up ISO on the full frame, you could potentially have a higher shutter speed. The lens on the full frame camera would weigh 1.8 pounds. Got it. :smile:
     
  12. coffeecat

    coffeecat Mu-43 Top Veteran

    708
    Aug 4, 2012
    SW England
    Rob
    There's a good article (well it appeals to my mathematical/engineering side) here:

    http://www.dpreview.com/articles/6091822765/background-blur-and-its-relationship-to-sensor-size

    There's some actual algebra in it, albeit very basic.

    I was struggling with the fact that equivalent DoF does not equal equivalent background blur, but this kind've put me right.

    It was the reason why I then went out and got me an 85mm f/1.8 legacy lens as a partner to my O45. Probably won't get much use, but will be useful now and then :)

    Rob
     
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  13. monk3y

    monk3y Mu-43 Hall of Famer

    May 14, 2013
    in The Cloud...
    Steven
    I think debating over this is not necessary... I have shot Fullframe, APS-C and m43 and from using them alone I can conclude that they gather more or less the same amount of light at the same settings. Sure they have a bit of variance due to Sensor, ISO ratings, lens and other factors but overall I don't think there's any significant difference in light gathering at all.

    Background blur is a different matter altogether.
     
  14. demiro

    demiro Mu-43 Hall of Famer

    Nov 7, 2010
    Thanks Rob. I will check it out. I'm OK with Algebra. After that things started to go sideways on me...