Should 4/3 lenses be half the size of full frame lenses?

Discussion in 'Digital Cameras' started by bob, Jun 13, 2011.

  1. bob

    Paul Furman Guest

    Right, that would make the images and exposures identical. ISO could
    compensate for the difference in sensor size. In the same way, an FX
    camera stopped down to match the DOF 'equivalent' of a smaller format
    would look just as grainy since you'd have to boost the ISO, assuming
    hand held shutter speed limitations. That would level the playing field.
    Paul Furman, Jun 15, 2011
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  2. Sure is. Ergo, one half of 36x24 is 18x24. That's a half frame, and always
    has been.
    A quarter of the area would of course be a quarter frame, not a half frame.
    In "its common-day usage," a half frame is half a frame, whether
    "specifically photographic" or not. Take a 36x24 frame and cut it exactly in
    half, and what do you have? An 18x24 piece, a half frame. This applies to
    any sort of rectangle I can think of.
    Neil Harrington, Jun 16, 2011
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  3. I remember your mentiong that sort of optical device before, Paul. But it's
    mostly all Greek to me. I do get (I think) the idea of a reducer lens
    increasing effective aperture by acting as a tele converter in reverse,
    though it sort of boggles my mind. But in that case the system would
    actually *become* the faster aperture, wouldn't it, just as an f/2.8 lens
    with 2x tele converter becomes an f/5.6 system?
    An "actual f/1.4" lens is one with a maximum effective aperture 1/1.4 of the
    focal length, eh? Does "f/1.4" have any other meaning than that? I don't
    understand what "equivalent f/2.8" even means in this connection.
    No doubt.
    Neil Harrington, Jun 16, 2011
  4. []
    The topic is "4/3 lenses compared to full-frame lenses". 4/3 has
    approximately half the linear dimensions of full-frame, and it is that to
    which I was referring, as I have clarified several times.

    A half-pint glass doesn't have half the linear dimensions of a full-pint
    glass, otherwise it would be a one-eighth pint glass! <G>

    David J Taylor, Jun 16, 2011
  5. Of course. The tele converter spreads the image onto a larger
    area (thus less light reaches the sensor (and the f/number rises
    accordingly), but you could use a larger sensor --- theoretically
    at least). The reducer concentrates the image onto a smaller area,
    the f/number shrinks accordingly ... and a smaller sensor than
    usually for the lens without the reducer is needed, or you'll
    get dark corners.

    An f/2.8 fullframe lens with a 2x teleconverter (between lens
    and sensor[1]) is a f/5.6 optic filling a 2x2 field of fullframe
    sensors , the same lens with a 2x 'telecompressor' would be a
    f/1.4 optic --- filling a "quarter fullframe" sensor.

    The famous 50mm f/0.7 was a reduced 80mm f/1.0. IIRC there were
    just 4 mm between lens and film.


    [1] There are teleconverters and wide angle converters you can
    screw in front of the lens, but they don't change the f/number.
    Unfortunately, they reduce the image quality, which is why
    you'll find them for P&S lenses (where you can't put them
    between lens and sensor)
    Wolfgang Weisselberg, Jun 16, 2011
  6. ISO is ISO, but the amplification it needs to reach said ISO is
    dependent on sensor quantum efficiency and sensor size.

    Wolfgang Weisselberg, Jun 16, 2011
  7. Is there *so* much difference between a 6MP camera and a 12MP
    camera downsampled to 4.3MP, and then optionally upsampled back
    to 6MP?

    - You have the same sensor area, and thanks to microlenses a very
    similar effective fill factor.
    - You incur SQRT(2) more read noise --- but read noise except
    for the darkest areas has little influence on total noise.
    - You have more information in a straight 12-to-6 MP downsample
    than a 6 MP camera delivers.
    - non-frame filling subjects (e.g. too distant for the tele end
    and you cannot get nearer) are better resolved with 12 MPix.

    The only real drawback is the larger image file size.

    100% crops aren't good to compare anything but per-pixel noise ---
    which is only valuable on identical pixel counts. (Noone looks
    at *photos* at 100%, because they cannot see the image then.)

    Wolfgang Weisselberg, Jun 16, 2011
  8. bob

    Guest Guest

    i've been completely consistent. if you think i skip around, then you
    don't understand it.
    all else is *not* equal if you ignore noise and depth of field.
    however, it's correct.
    Guest, Jun 16, 2011
  9. bob

    Guest Guest

    that will get you the same exposure, but *not* the same noise or depth
    of field.
    which is why you raise the iso of the larger format to use 2 stops
    slower. then the exposure is the same, as well as noise and depth of
    which is why you have to normalize it for equivalency.
    Guest, Jun 16, 2011
  10. bob

    Guest Guest

    equivalent image, including dof & noise. you don't get to pick and
    choose which ones qualify as equivalent.
    Guest, Jun 16, 2011
  11. Yeah, not really so bad. I have a personal problem with
    a workflow that involves deliberately throwing away information,
    though, which ends up meaning I see the junk when I'm
    working on the photo.
    I work at 100% a lot while retouching. Or 200%.
    David Dyer-Bennet, Jun 16, 2011
  12. But if you gave that pint glass to someone with a suitable glass cutter and
    told him to cut it in half, which would reduce only the height dimension, it
    would be a half-pint glass.

    Of course if he cut it in half lengthwise it wouldn't hold anything at all,
    which would be a shame. :)
    Neil Harrington, Jun 16, 2011
  13. bob

    J. Clarke Guest

    Fine, take a 4/3 and a full frame and shoot the same scene at the same
    ISO and shutter speed with both, with the full frame at f/2.8 and the
    4/3 at f/1.4 and show us your results.
    J. Clarke, Jun 16, 2011
  14. Of course.
    Which changes something else entirely.
    No, the ISO remains the same. What "you have to" do to achieve some other
    purpose, however appropriate and useful that might be, does not change the
    Neil Harrington, Jun 16, 2011
  15. Sure. Whatever.
    Neil Harrington, Jun 16, 2011
  16. There's nothing to "pick and choose." The f-number means: the focal length
    divided by the physical size of the aperture. That's why it's written that
    way, and that's all it means.
    Neil Harrington, Jun 16, 2011
  17. That wouldn't change the f-number. A different and I think more direct way
    of saying what you're saying is simply that (for example) a 2x tele
    converter doubles the focal length, thus doubling the f-number as well since
    the maximum aperture remains the same. All f/2.8 (for example) means is that
    the aperture size is the focal length divided by 2.8 -- which is why it's
    written just that way.
    Interesting. I had never heard of that one.
    Neil Harrington, Jun 16, 2011
  18. You are probably consistent in your own mind, which involves mixing all
    sorts of things together that we are not really talking about.
    Noise and depth of field are not what we are talking about, however
    important they may be in some other connection.
    No. You apparently have some sort of "equivalence" in mind that does not and
    cannot actually exist. When you change sensor size you change several
    characteristics, such as those you've mentioned, which have nothing to do
    with equivalence in exposure.
    Neil Harrington, Jun 16, 2011
  19. bob

    Guest Guest

    that means the images are not equivalent, they just have the proper
    right, it matches the noise of the smaller sensor and lets you use a
    smaller f/stop so you can match depth of field. that way you get an
    equivalent image.
    if the iso remains the same you have less noise on the larger sensor,
    so it's not equivalent.

    it's really quite simple.
    Guest, Jun 17, 2011
  20. bob

    Guest Guest

    an f/number by itself is independent of any sensor size. once you put
    it on a camera, you *must* take into account the size of the sensor.

    you're also ignoring other characteristics of the image.

    if the noise and depth of field are different, the image is *not*
    equivalent. you do not get to pick only one thing.
    Guest, Jun 17, 2011
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