Aperture Ranges on Ultra-Compact Digitals

Discussion in 'Mirrorless Digital Cameras' started by at_nick, Nov 8, 2005.

  1. Im wondering why the ultra-compact digital cameras seem to have
    limited abilities for closing down the apertures. For example, the
    smallest aperture on the Leica D-LUX 2 is f/8. Is this because the
    optics are so small on the ultra-compact point-and-shoots?

    How would the depth-of-field at f/8 on a camera like this compare to
    the same shot at f/22 on a DSLR?
     
  2. It has to do with the size of the sensor. Diffraction limits sharpness at smaller apertures,
    but in inverse proportion to the size of the recording medium.

    My 4x5 lenses go to f90!

    DOF is controlled by 1) aperture, and 2) reproduction ratio. If you make an 8x10 print
    from 35mm film or from a tiny digital sensor at the same aperture and same reproduction
    ratio, they will have the same DOF. Therefore, digital cameras have less DOF when
    displaying the same information at the same size at the smallest available aperture.

    You *could* make a digicam go to f22 or smaller, but it would get fuzzy because of
    diffraction.
     
  3. Take a look at this article

    http://www.bobatkins.com/photography/technical/diffraction.html

    The smaller the sensor, the more the image is degraded by diffraction.
     
  4. As a first approximation, you can multiply a digicam aperture by the crop factor relative to 35mm to get the equivalent aperture for DOF on 35mm. I can't be certain of the exact size of a non-standard 1/1.65" sensor, but I would guess the sensor diagonal is around 11mm (since it is presumably almost identical to 2/3" sensor dimensions), compared with ~43mm diagonal of a 35mm frame - so the crop factor is ~4, and therefore f/8 is about equivalent to f/32 (including the diffraction influence).

    The real limitations on digicams are in fact on their wide apertures. The fastest possible lens on theoretical grounds is f/0.5, which would only equate to f/2 in 35mm DOF terms (reality is that lens cost increases dramatically as apertures are widened partly because it becomes very difficult to correct aberrations - think of the price and size of a Noctilux f/1.0 50mm for Leica M).

    The other argument for needing faster lenses on digicams is that noise rapidly becomes apparent as you increase ISO, therefore you need to be able to compensate by using a slower ISO and a faster lens in order to get a fast enough shutter speed to freeze motion and cut down on camera shake while avoiding undue image noise.
     
  5. The current setup is better than most any alternative if you want to keep your camera small.

    Have you ever looked at 35mm point & shoot camera zooms? The lenses on those cameras cover a 35mm piece of film, but what you get at the long zoom end is a maximum aperture usually of something around f8 or f11- totally unusable in anything other than good lighting. To make them faster would require building a much bigger camera overall, just as making a digital point& shoot that could effectivly stop down to f22 would require a much bigger set of lens elements, hence a bigger body. Making the sensor smaller with faster maximum aperture to me at least is preferable.
     
  6. Other than the control of excess light, the primary use of aperture control is to establish how much of a shot is in focus (depth of field). My understanding is that small sensor digicams have a very large DoF, even at large apertures (e.g f/2.8). That?s certainly a "better or worse" fact of life, but the punchline is that f/8 should certainly be effective for doing high-DoF shooting (e.g. landscape photography).
     

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