The myth of the "smaller" 4/3rds lens

Discussion in 'Digital SLR' started by RichA, Oct 12, 2006.

  1. RichA

    RichA Guest

    That is only by making lens surfaces more curved (to increase
    magnification or reduce it more) in a given space. Also, extensive
    and expensive use of ED and other exotic glasses helps allow this. But
    people have to remember that lenses cannot "shrink" beyond a certain
    point and it has NOTHING to do with sensor size. A 200mm f2 lens STILL
    needs a 100mm wide front element to claim it is 200mm f2 (200/100 =
    2). The REASON it seems that Olympus can make "smaller" lenses is
    because a 200mm lens on a Full frame or 1.3-1.6 cropped sensor
    provides a wider angle of view than the 2x Olympus that in-turn allows
    Olympus to put more pixels into a given area of a scene, and resolve
    more detail for a given lens focal length (provided both the Olympus
    and the other brand have the same pixel count). So the proverbial
    300mm lens on the 2x sensor functions like a 400mm lens on a FF
    camera. The reciprocal being that you cannot get as wide a view with
    an Olympus sensor as with a larger sensor because it would require
    making lenses with shorter focal lengths. The shortest lens I've ever
    seen was Nikon's 6mm which on a FF SLR has twice the field of view as
    a 4/3rds camera.

    But, if someone is thinking Olympus can produce a 300mm f2.8 lens any
    smaller than Canon, they would be dead wrong. The lens STILL needs a
    107mm of clear front aperture to meet it's speed claim.
     
    RichA, Oct 12, 2006
    #1
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  2. RichA

    bmoag Guest

    There is ongoing research into ways to focus light for photographic use that
    does not totally rely on glass/plastic as we know it particularly for use
    with very small sensors.
    The technology of imaging is evolving in ways that will not rely on
    traditional materials just as digital sensors have replaced film for most
    uses.
    Bigger is not better even at this point in the development of digital
    photography and will come to be seen as the liability it has always been
    when better technical solutions become available.
     
    bmoag, Oct 12, 2006
    #2
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  3. The flaw in this logic is number of photons. A smaller
    camera with a smaller aperture lens collects fewer photons.
    The signal-to-noise ratio in digital camera images is directly
    related to the square root of the number of photons collected
    in each pixel. Smaller pixels with smaller photons collected
    also results in smaller dynamic range.

    http://www.clarkvision.com/imagedetail/does.pixel.size.matter

    Roger
     
    Roger N. Clark (change username to rnclark), Oct 12, 2006
    #3
  4. RichA

    Mark² Guest

    You can't simply "get smaller" without reaching a point that bumps up
    against limitations rooted in the properties of light itself. Others here
    have discussed this at length (Think Roger and David Littleboy).
     
    Mark², Oct 12, 2006
    #4
  5. Why would you make such a point of this.. and then go about telling us
    the opposite? Of course sensor size makes a difference, *for a given
    angle of view*! And if you don't hold the angle of view constant for
    comparing whether a given camera/lens combination is bulkier than
    another, then what is the point?? Yes, we know about sensor noise
    issues, but this was about lens size/bulk.
    Umm. Forgive my pickiness - I'm a bit rusty on lens design. But is it
    the *front element* that gives the aperture calculation???? I mean I
    realise it has to be a certain size to allow the lens to operate to
    it's full 'f' capability, but isn't it the APERTURE that is used for
    calculating the f-ratio? Ie the IRIS opening, not the front element.
    I humbly apologise if I'm wrong, and I realise they are of course
    related, but let's be *accurate* here...
    As per my initial comment - DUUUH!
    Am I missing something here as well? It's a 2x multiplication factor,
    and yet Rich says a 300 goes to ..400? Umm, yeah right...
    Sigh. Never looked at a video camera or a compact?
    Err, say what? I missed the point of that line.. Yes, to match that
    6mm lens, Oly would have to create a 3mm. Challenging? Yes indeed.
    But how many 6mm (35 equiv) owners are there around here? (That 6mm
    lens, if mounted on the Oly, would act like a 12mm (35 equiv) extreme
    w/a, and I doubt *many* folks would be agonising that they couldn't go
    wider...
    But they *can* create a 150mm f2.8 that is smaller and is the
    EQUIVALENT lens in terms of field of view. Sigh.
    Now it's 'front aperture'? See comment above. Happy to be corrected...
     
    mark.thomas.7, Oct 12, 2006
    #5
  6. RichA

    J. Clarke Guest

    While it is in principle possible to make a flat camera that from a
    magnification viewpont has a very long lens or one that from a depth of
    field and sharpness viewpoint has a very wide aperture using techniques
    developed for long-baseline interferometry, the difficulty with these
    techniques is that you don't get the sensitivity normally associated with
    those large apertures. I can't see this approach as being other than a
    niche solution.
     
    J. Clarke, Oct 12, 2006
    #6
  7. RichA

    acl Guest

    Roger,
    I don't think anybody implied a smaller aperture here. Yes, you'll
    always need a large area to collect photons from (the "front element"),
    but the rest of the "lens" (length etc) is not fixed by physical
    considerations.

    Take a look at this:
    http://prola.aps.org/abstract/PRL/v85/i18/p3966_1

    Cheers!
     
    acl, Oct 12, 2006
    #7
  8. RichA

    acl Guest

    Mark,
    When it comes to lenses, the only physical limitation is the
    relationship of the area from which light is collected ("front element")
    to the magnification of the image on the sensor. The rest is only
    determined by what we use to make the lenses (currently, glass).
     
    acl, Oct 12, 2006
    #8
  9. RichA

    Paul Furman Guest

    Paul Furman, Oct 12, 2006
    #9
  10. RichA

    J. Clarke Guest

    If it could be scaled to the dimensions required for photographic lenses
    (the uses described seem to be on a very short distance scale) then it might
    yield a lens sharper than current technology, but photographic lenses are
    seldom diffraction-limited at large apertures anyway, so it would seem to be
    a nonstarter.
     
    J. Clarke, Oct 12, 2006
    #10
  11. So when will we get these portable gravitic lenses?
    And will we need a huge truck for the power requirements, or
    will there be a hip-pocket fusion plant to go with it?
    That must be why the APS films were such a rage and outsold
    everything else. Oh, no, wait, that's the reason every
    self-respecting photographer uses a Minox instead of small, medium
    or large format, and why all the digital cameras are modelled
    after the Minox cameras ... instead of these large rectangles,
    which you can hardly put into a small pocket or up your sleeve.

    -Wolfgang
     
    Wolfgang Weisselberg, Oct 12, 2006
    #11
  12. The idea is that it's a nontraditional way to focus light.
     
    achilleaslazarides, Oct 12, 2006
    #12
  13. "negative refractive index material" means that the speed of light is
    higher than c within that material, while this is not strictly
    impossible, it can only be obtained by quantum effects. And those
    usually have a major statistical behavior, which supposedly imposes noise.

    -Michael
     
    Michael Schnell, Oct 12, 2006
    #13
  14. c>1 is, in fact, strictly impossible (for the group velocity of light,
    which is what is of interest here). What "negative refractive index"
    means in this context is a bit more technical, and in Pendry's paper he
    actually considers a material for which the dielectric constant and the
    magnetic permeability (which describe the response of the material to
    applied electric and magnetic fields, eg light) are negative. Their
    product is still positive, and so the speed of light is not different
    from free space. Of course, this is an approximation, in actual
    experimental realisations it'll be slower.

    And reasoning that quantum effects always induce noise is simply
    untrue: Consider solids, which only exist because of quantum mechanical
    effects. Or, to take a more obvious example, a Bose-Einstein
    condensate: a purely quantum effect in which all the particles behave
    in an identical way even at finite temperature. Quite the opposite of
    what you'd expect!
     
    achilleaslazarides, Oct 12, 2006
    #14
  15. RichA

    RichA Guest

    I don't think this "holy grail" of refraction has been used across the
    visible spectrum yet.
     
    RichA, Oct 12, 2006
    #15
  16. RichA

    RichA Guest

    The general rule in lens design is you never use more aperture than you
    have to.
    Which means the front lens diameter (what isn't cut off by any
    retaining rings) is the aperture. However, it is possible that some
    lens designs have been made using a larger size than true aperture once
    internal body "stop downs" have been used. This would be used in a
    case where CA or some other aberration could be controlled in no other
    way, but it's rarely used because the cost of lens fabrication and
    materials rises exponentially with element diameter. The iris opening
    does dictate the aperture, but the iris in most lenses should open
    nearly as or as wide as the element's front aperture. Waste not....
    No, the angle of view is 1/2 of that in a FF camera, so the 300mm on an
    FF = 600mm on the 2x.
    You'd be amazed how many FF Canon shooters regularly use 17mm or wider
    lenses.
    I'd venture very few 4/3rds owners will have a 8-9mm lens available.
    That is true, but it is NOT the same as making a 300mm smaller than
    another 300mm. I was talking about lenses of the same f.l., not lenses
    that were equivalent in action on the two different sensors.
    As I said, in most lenses the front aperture IS the full aperture and
    determines the focal ratio. However, we are talking about normal and
    tele lenses and NOT wide angle lenses that have completely different
    characteristics. Which is why Olympus's old 8mm fisheye has a front
    element about 120mm wide. If you compare the old OM 8mm with the new
    one,
    the new one (made to support 4/3rds instead of FF) is substantially
    smaller.
     
    RichA, Oct 12, 2006
    #16
  17. I was merely trying to point out that various "physical limits" aren't
    as hard as they would appear. Others are, of course.
     
    achilleaslazarides, Oct 13, 2006
    #17

  18. Hmm.... The beginning of my reply disappeared, somehow. It should have
    read something like:

    The refractive index n is usually defined as the ratio of the speed of
    light in vacuo and in a material; thus, what you say would refer to n<1
    rather than n<0. At any rate,
    c>1 is, in fact,.......


    Apologies.
     
    achilleaslazarides, Oct 13, 2006
    #18
  19. The accurate answer is the entrance pupil determines the true
    aperture. The front element must be at least the true aperture,
    or you don't get the full amount of photons. Typically, the
    front element is larger than the entrance pupil. The iris
    diaphragm may be much smaller as the lenses in front of the
    iris usually focus the light into a smaller cone. The entrance
    pupil is not necessarily a physical aperture. It gets
    quite complex in the many element lens designs for modern cameras.
    The problem with reducing the lens aperture is that it collects
    fewer photons. So in the equivalent field of view same
    megapixel count camera scaling, the 300 f/2.8 collects
    4 times the number of photons as the 150 mm f/2.8.
    So the two cameras may produce the same resolution images,
    but the smaller camera image is 2x noisier for the same exposure
    time.

    Roger
     
    Roger N. Clark (change username to rnclark), Oct 13, 2006
    #19
  20. You *do* seem to be fixated on photon noise. (O;

    In my response, I said:
    I thought that was sufficient, given the topic.

    Roger:
    But hang on - first up, we are talking about two completely different
    camera formats, and noise may or may not be an issue. Is noise an
    issue on a Hassy back? On a Canon 1DS MkII? On a Nikon D2X? On a P&S?
    Yes, of course at some point it becomes an issue, but you can't just
    blithely say it is 2x noisier and seemingly dismiss the concept.

    Given possible improvements in sensor design (- I seem to recall that
    when pushed you admit that there is probably at least another factor of
    30% or so left for improvements in processing, more efficient sensor
    packing, different designs of wells, microlenses etc), and the fact
    that already many sensors *somehow* perform well beyond their weight
    (eg the Fuji sensor designs, the F30, the larger canon CMOSes) - I
    don't believe that 4/3 is too small to ever have a really good
    low-noise sensor, which is the implication..

    In other words, it may indeed be "2x noisier", but if the noise is so
    low that a 2-fold increase is still very low-noise, who cares? In
    theory you could shrink the best Canon FF CMOS to 4/3... and it would
    be 2x noisier... Do you think anyone would be complaining much about
    those noise levels?

    Like I said, this post was about the alleged "myth of smaller 4/3
    lenses". There is no myth. You can make a smaller lens, given a
    smaller sensor. *At some point* sensor noise may/will become an issue,
    but to say that 4/3 is that point reminds me of some Arthur C Clarke
    quotes:

    Any sufficiently advanced technology is indistinguishable from magic.

    Every revolutionary idea seems to evoke three stages of reaction. They
    may be summed up by the phrases: (1) It's completely impossible. (2)
    It's possible, but it's not worth doing. (3) I said it was a good idea
    all along.

    If an elderly but distinguished scientist says that something is
    possible, he is almost certainly right; but if he says that it is
    impossible, he is very probably wrong.
     
    mark.thomas.7, Oct 13, 2006
    #20
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