Interesting Panasonic TZ1 feature

Discussion in 'Digital Photography' started by ~~NoMad~~, Jun 29, 2007.

  1. ~~NoMad~~

    ~~NoMad~~ Guest

    After owning a TZ1 for over a year now, I just noticed an interesting

    The TZ1 has only two aperture settings F2.8 and F5 at wide angle. Zoom it
    out 10x and the two settings become F4.2 and F7.1. No wonder they don't have
    a manual mode in this camera with only two aperture settings. I haven't
    noticed any abnormal loss in Depth of Field with this camera and I consider
    the pictures it produces excellent.

    I wonder if other P&S cameras have the same limited aperture settings?

    ~~NoMad~~, Jun 29, 2007
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  2. All small-sensor cameras are limited in the smaller physical apertures
    (higher f/numbers) because of the onset of diffraction effects at the
    smaller apertures restricting image sharpness. At f/16, the pictures
    would be noticeably worse. If they don't have a big maximum aperture,
    then the f/number range may indeed by quite restricted.

    David J Taylor, Jun 29, 2007
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  3. ~~NoMad~~

    Nervous Nick Guest

    That raises an interesting question: Have any *empirical* studies
    been done regarding small-sensor cameras (or, rather, very short focal-
    length lenses), WRT at what point the lenses become diffraction-
    limited? I am relatively new to digital photography, and initially
    found it difficult to remember that you just plain cannot stop a lens
    down on a digital camera as much as you might unthinkingly do with a
    larger format camera.
    Nervous Nick, Jun 30, 2007
  4. [A complimentary Cc of this posting was sent to
    Remember the scaling law w.r.t. the sensor size. One can get
    identical pictures from sensors of different sizes, PROVIDED (quote
    from my older post):

    The physical laws of scaling are the following: to produce the same
    image from N times smaller sensor (linearly) one needs to:

    a) have the same count of pixels;

    b) have the same QE;

    c) have the same readout noise;

    d) have the same full well;

    e) have the same exposure time;

    f) use N times higher aperture (measured as an F-number, e.g., 1/45);

    g) have the same "quality" of the lens (e.g, measured as quotient
    of actual MTF of the lens to MTF of diffraction-limited lens)

    So, e.g., comparing 1/2.5"-sensor with full-frame (which is 8/3"), the
    aperture is translated to 2.8*N, 5*N, 4.2*N, and 7.1*N, with N being
    8/3/(1/2.5)=6.6. This makes your apertures equivalent to f/19, f/33,
    f/28 and f/47 (when comparing to full-frame).

    I do not know the sensor size of TZ1, so you may need to recalculate.
    Anyway, did you ever used apertures much smaller than f/47 with
    full-frame? 1/4 ;-)

    Hope this helps,
    Ilya Zakharevich, Jun 30, 2007
  5. Nervous Nick wrote:
    I do hope someone can answer your question, but knowing the way in which
    marketing /can/ drive engineering, I suspect that cameras are already at
    or beyond that limit! However, as people's expectations may be less with
    small-sensor cameras, perhaps it doesn't matter as much if some
    diffraction shows. I think it would just be a lack of sharpness rather
    than anything unpleasant. To keep noise down, you may stick with ISO 100,
    so not having a smaller aperture may not matter as much. In any case, you
    already have greater depth-of-field.

    David J Taylor, Jun 30, 2007
  6. ~~NoMad~~

    Nervous Nick Guest

    So you seem to be saying that most of these lenses would be
    diffraction limited when *wide open.* Which makes sense considering
    the much smaller scale we are talking about.*

    However, as people's expectations may be less with
    See, there is where I got messed up initially; in thinking that you
    would get greater depth of field by stopping down, when you already
    *have* that greater depth of field inherent to the smaller scales.



    *By "a point where a lens becomes diffraction limited* I mean, the f-
    stop past, where if you stop down any further, you get no net gain in
    sharpness, and indeed begin to experience loss in sharpness. You can
    actually view this phenomenon under an enlarger, for example, if you
    carefully look at film grain through your enlarging magnifier while
    stopping down the lens. As you stop down, the grain will appear to
    become sharper, up to a certain f-stop, past which the sharpness
    degenerates. It is at that crucial f-stop that the lens is said to be
    "diffraction-limited," as in, for example, "diffraction-limited at f/
    Nervous Nick, Jun 30, 2007
  7. ~~NoMad~~

    Eddie Guest

    ~~NoMad~~ presented the following explanation :
    Yes, my Casio EX-Z850 has the same feature. 2 f-stop settings per
    Eddie, Jun 30, 2007
  8. Nervous Nick wrote:
    I haven't done the sums, but, yes, that is possible.
    Yes, it's one of the prime differences between small-sensor cameras and
    DSLRs. On the small sensor camera there is less need to stop down to
    increase DoF. Of course, sometimes you want a large DoF to have
    everything sharp, and sometimes a small DoF to isolate the main subject.
    In practice, I find that with the longer end of the zoom (say 200mm+) on a
    Panasonic FZ5, you can isolate the subject quite well, but you could do so
    at a shorter focal length (say 50mm) on a DSLR with an f/1.8 lens.

    David J Taylor, Jun 30, 2007
  9. ~~NoMad~~

    Alex Monro Guest

    You might find this web page of interest:
    Alex Monro, Jun 30, 2007
  10. [A complimentary Cc of this posting was sent to
    Nervous Nick
    This would not make any sense. The lenses are so tiny, that making
    them 1.5 as large would not add more than a few cents to the cost.

    If they were diffraction-limited at f/1.5N, they would be of quite good
    quality at f/N. You gain a full f-stop with very minor change in price.

    But what I *have* seen is that some of the best P&S cameras give the
    *best resolution* when wide open. This means that they are not
    diffraction-limited when wide open, but not-very-far-away-from
    diffraction-limited when wide open.

    (E.g., IIRC, G5 has its best resolution at f/2.8.)

    Hope this helps,
    Ilya Zakharevich, Jul 1, 2007
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