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narrower aperture = lower resolution?

Discussion in 'Open Discussion' started by noelh, Jan 8, 2013.

  1. True or false? mu43 format, narrow aperture (>f5.6-8ish) results in lower resolution due to diffraction.

    Checked out my set of native mu43 lens. They all max out at f16 or f22. Do people really need the dof or slower shutter speeds of these small apertures? I'm assuming it doesn't require any significant additional costs to design and manufacture a lens that maxs out at f8 vs. f16/22. So the makers do so and just use it as a spec. feature for advertisement.
  2. vinay

    vinay Mu-43 Regular

    Mar 18, 2012
    I use tiny apertures for long exposures or when i'm trying to get some DoF at macro distances.
  3. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL
    more like "mins out". Maximum aperture is at the other end of the scale.

    Yes, using a small aperture (read: toward f/22 or further) will possibly reduce resolution. At what aperture this diffaction event begins to show its ugly head varies with the focal length and with the quality of the lens (the better the lens the sooner it shows). It has absolutely nothing to do, at least directly, with the film/image format.

    A perfectly made lens will deliver its highest resolution wide open. Diffraction will reduce the resolution if the lens is stopped down even slightly. The further you close the aperture the greater the reduction in resolution. But...

    ... no lens is perfect. Stopping down often reduces the impact of flaws and compromises in the optical design. In practice, a real world lens will deliver somewhat better resolution as you stop down, at least up to a point. At some point you run up to the resolution limit set by the smaller aperture. It is something telescope designers refer to as "Dawe's Limit" and it a factor of the wavelength of light. Also, it is a factor of the absolute diameter of the aperture and not the ratio of that diameter with the focal length (read: "f/stop" to photographers and "focal ratio" to the telescope crowd)

    In practice, the lenses commonly used on m43 (e.g. 12-50mm) will begin to show the impact of this limit at around f/4-5.6 and will become completely limited by diffraction at around f/8. After that it is all downhill. Because it's the absolute diameter of the aperture that is a controlling factor, the shorter the focal length the wider the f/stop is when the limits are reached. Short lenses for m43 (7-10mm) will show issues at apertures as wide as f/4 if there are well enough designed though in practice there will be some improvement as a result of the reduction in flaws/compromises down to f/5.6 or f/8.
  4. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    As almost always. Yes and no.

    Diffraction begins somewhere around f8-f11 on a m4/3 sensor but it's not an absolute. It's not like it goes from 0 to 100% instantly. The effect of diffraction comes in gradually. But you'll notice it between f11 and f16 usually. BUT...

    There are other things that will either magnify or hide its impacts. Do you have an optimal exposure? How big is the print? Are you cropping? Is the camera perfectly sharp at a pixel level? Did you get a tripod? The list goes on and on and on.....

    Personally if I'm shooting on a tripod using a release, while shooting a landscape with lots of detail that I'm going to print really big, then I'll be concious of difractrion. For a handheld portrait of a black cat in a dark room I've got other things to worry about.

    As always. Do some tests. Print to your normal sizes and see if it matters (or where it begins to matter) for your specific needs.

  5. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Of course it does. A smaller sensor requires a greater enlargement faactor to make the same sized print as a larger sensor would. This has a direct effect on when diffraction becomes noticable.

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