On Sharpness, ISO and Shutter Speed

Started Nov 29, 2013 | Discussions thread
RussellInCincinnati Veteran Member • Posts: 3,201
reasons tripod APS-C typically sharper

Chris Malcolm wrote: Of course the much bigger ...shutter and mirror machinery of full frame DSLRs is a more serious [sharpness] problem. I'm surprised more people haven't remarked on that as a reason to prefer APS-C.

Not hard to guess why lighter, smaller-shutter APS-C cameras would be sharper (and in my experience are, in the field) than heavier, bigger-shutter, perhaps flipping mirror, full frame sensor cameras, on a tripod, on average. Particularly for typical portraiture angle of views.

F/2.2 is not exactly this (literally throw-away/cheapest of all Minoltas AF) 50/1.7 lens' optimum aperture. Here on APS-C mirrorless camera sensor, with no first curtain electronic shutter feature or remote activation, on a fairly flimsy 1200 gram tripod.

Let's define "perfect sharpness" as resolving single-pixel-width details, to within the symmetrical-blurring contrast capability of the lens, camera body/sensor and anti-aliasing filter.

On "smaller-sensor" cameras (e.g. APS-C), you end up, on average, getting "perfect sharpness in the field", i.e. something close to the potential sharpness of ordinary lenses and sensors compared to full frame cameras because you are using

  1. Lenses that are usually physically shorter and lighter for a given angle of view, thus the camera rig jiggles less on a given tripod. Sure the new Sony FE 35/2.8 is only 130 grams, but the not-terribly-different-angle-of-view Sony 20/2.8 for APS-C is 70 grams. And someone please inform me if there are 220-gram full format 28-85-type kit zooms of decent optical quality, like there are for APS-C.
  2. Camera bodies that are physically shallower and lighter, thus the camera rig jiggles less on a given tripod.
  3. The smaller-sensor cameras tend to be mirrorless, since people buy them instead of "full frame" to get to some configurations that are smaller than full frame cameras. So there goes the mirror vibrations.
  4. As Chris Malcolm mentioned above, what shutter vibrations one does get from a certain design, are from a smaller shutter in any case.
  5. Lenses that are shorter focal length, thus tending to have higher (at least central) sharpness
  6. For portrait (mild telephoto) focal lengths, on APS-C the compact lenses you get to use usually have a relatively simple and symmetrical, certainly well-refined planar/double-Gauss lens designs

    Quick, which of these lenses is the Zeiss Planar designed about a century before the other one.

    instead of harder-to-get-perfectly-sharp-at-wide-apertures telephoto lens designs. Consider the near-worthless plastic kit "normal" lens from the 1980's, used above for mild telephoto portraiture on a smaller APS-C sensor. Most of those lenses function at the same clarity level, at the quite wide apertures of many a portrait, as a high-end full-frame sensor telephoto optic, that is on average more massive and jiggly on a tripod.

  7. For a given travel kit weight budget, the smaller format cameras make it practical to carry a collection of ridiculously light (e.g. 70 gram!), fast prime lenses, instead of a single larger-format 500-1000 gram fast zoom lens. Maybe the kit weight is the same, but the weight and thus stability of the bunch-of-little-primes rig on the tripod for any given photo is much, much less.

My not-remote-actuated mirrorless APS-C Nex C3 portraits with cheap, decades-old lenses are on average noticeably sharper than was ever able to get out of my relatively huge, flipping mirror medium format Mamiya, Which had rather expensive and well-made, conservatively designed F/4 portrait and macro prime lenses. Even though used a remote shutter release for the medium format cam that was on a tripod much heaver and more solid than would tolerate today.

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