Confused about apertures on different formats

alaiosalaios Registered Users Posts: 668 Major grins
edited May 3, 2015 in Technique
Dear all,
I have heard many times that a full frame camera has always a light advantage at the same aperture compared with smaller sensors (i.e aps-c).
Their trade off is that they lose in depth of field but still I Try to understand that light advantage.

If a full frame camera and an aps-c camera are both set to f2.8 the full camera would get more light, since the 2.8 at actual dimensions is larger on a full frame camera.

Is not that right?
If yes does not mean tha for the same light and same aperture shutter speed combinations the full frame camera would need less iso?

I did the following experiment.
I grabbed my aps- camera and I found that the exposure for a specific light conditions was iso 1600, 1/30 f 2.8
Then I picked the full frame with exact depth of field (my aps-c camera had a 30mm lens while my full frame camera had 45mm)
and I tried to find the same exposure. I got exactly the same settings so 1/30, f/2.8 iso 1600.

Are these number correct?

Regards
Alex

Comments

  • AndyAndy Registered Users Posts: 50,016 Major grins
    edited May 1, 2015
    Light is light. And f/stops are f/stops. Doesn't matter what format you are using. What does change, however, is the effect of the aperture on different sensors. f/2.8 on full-frame CaniSonikon will have less depth of field than if you used f/2.8 on a smaller-sensor camera, like an APS-C or a Micro 4/3s camera, or heck, even a camera phone. Also, the out-of-focus areas, and the quality of the bokeh, will be different bases on sensor size. A m43s camera at f/2.8 will have the same light-gathering ability as a Nikon D810 with a lens at f/2.8 - but - the smaller sensor camera will have a greater depth of field. With my small mirrorless camera, for typical shots with lots of depth of field, I can shoot at f/5.6 and rarely have to go to a narrower aperture - it's roughly equivalent (to my experience and eye, I haven't done any measurebating on this subject) to my shots with a Nikon D810 at f/8 or 11.
    Andy

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  • pathfinderpathfinder Super Moderators Posts: 14,708 moderator
    edited May 2, 2015
    The beauty of using stops, is that, like Andy said, an f 4 lens 28mm admits the same exposure/amount of light as an f4 500mm lens - no matter whether the lens is on a FF, crop sensor, m4/3 or a point and shoot, and hence the shutter speed would remain the same as you just experienced, Alaios. The depth of field and out of focus areas WILL vary on different format camera for a given focal length, even though the aperture,shutter speed, ISO relationships do not change.
    Pathfinder - www.pathfinder.smugmug.com

    Moderator of the Technique Forum and Finishing School on Dgrin
  • ThelensspotThelensspot Registered Users Posts: 2,041 Major grins
    edited May 2, 2015
    Andy wrote: »
    "I haven't done any measurebating on this subject"...

    A entire new vocabulary has just been opened up to me! Thanks Andy! thumb.gif
    "Photography is partly art and partly science. Really good photography adds discipline, sacrifice and a never ending pursuit of photographic excellence"...ziggy53

  • alaiosalaios Registered Users Posts: 668 Major grins
    edited May 3, 2015
    Got it .. so the f stop is similar in terms of light gathering capabilities on different sensor sizes.
    If I get this right then as you said the trade off is depth of field vs reachability (hmm there is no such word). Either you lose depth of field or you get more depth of field but more reach with a same lens.
    Is not that right?
    Alex
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