Olympus OM enthusiasts' digital prayers have been answered ...

Discussion in 'Digital Photography' started by Bruce, Feb 4, 2012.

  1. Bruce

    Bruce Guest


    Not only don't you understand what I wrote, but you seem wilfully
    determined not to understand. As I said, it's your loss, but you
    might like to consider the meaning of the terms "telecentric" and
    "oblique".

    As for experience, I have bench tested many lenses in addition to real
    world testing, and advised one of Europe's largest camera importers on
    the issue of compatibility of lenses that were designed for film with
    digital sensors. That involved testing every single lens in their
    current range, plus some older lenses, on their early digital SLRs.

    It was more of a problem with Olympus (Kodak) sensors than with other
    brands because the Kodak sensors were specifically designed to be used
    with near-telecentric lenses, and performed particularly badly with
    lenses that were far from telecentric. The Zuiko Digital lenses are
    remarkably telecentric and produced outstanding results on Kodak
    sensors.

    Alas, the OM Zuiko range included many lenses that were far from
    telecentric; Olympus's quest for small size and lightness meant that
    light rays from many Zuiko lenses hit the film/sensor at seriously
    oblique angles. Hence the need for Olympus to list (1) the lenses
    that would work well on digital, (2) the lenses that would work less
    well (perhaps with limitations on aperture) and (3) those that
    wouldn't work at all well.

    If there wasn't a problem, as you so confidently assert, why on earth
    would Olympus have gone to such lengths?

    Your Head In The Sand Club membership card is in the mail. ;-)
     
    Bruce, Feb 7, 2012
    #21
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  2. To justify making small 4-turds sensors in the first place!
    That's when they came out with the "telecentric is best for digital"
    myth in the first place and it was shortly proven to be wrong by
    measurement. The light fall-off due to non-telecentricity is *LESS* on
    Olympus (and Canon FF sensors for that matter) than it was on film!

    OM lenses work just as well on digital as they did on film, which
    doesn't mean telecentric lenses can't work better, but the argument was
    false to begin with and was merely an attempt by Olympus to justify
    their investment in cheap chips.

    Try the counter argument: if there was a problem, why are the 4-turds
    consortium the only folk that have it? Whilst Leica do take steps to
    reduce the issue on their sensor, neither Canon, Nikon nor Sony do.
     
    Kennedy McEwen, Feb 7, 2012
    #22
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  3. Which is just nonsense - I have several OM lenses that work just as
    well, perhaps even better, on my Canon FF sensors as they did on film in
    an OM body.
     
    Kennedy McEwen, Feb 7, 2012
    #23
  4. I have one, and the original OM lenses work very well on it thank you
    very much. In fact, I posted some measured results from them on this
    forum about 5 years ago - try Google!
     
    Kennedy McEwen, Feb 7, 2012
    #24
  5. That statement is simple repetition of Olympus's original false
    justification for making the 4-turds sensor smaller than FF in the first
    place, and that was disproved when FF sensors were demonstrated to work
    perfectly well with OM lenses. There is NOTHING in the Olympus sensor
    design which "strongly prefers telecentric lenses" and several 4-turds
    lenses are just as non-telecentric as their equivalent OM lenses were.
     
    Kennedy McEwen, Feb 7, 2012
    #25
  6. Bruce

    Pete A Guest

    Illumination falloff for a non-telecentric lens is approximately a
    cosine to the fourth power. The only way a digital sensor can suffer
    _less_ falloff than film is by altering the angle of the non-central
    micro-lenses. In all other cases, a digitital sensor will suffer more
    light falloff than film.
     
    Pete A, Feb 7, 2012
    #26
  7. Bruce

    Trevor Guest

    I only suggested it didn't match my experience and you have now explained
    why. Thank you!

    Your unnecessarily antagonistic club membership card is in the mail, no
    wait, not worth the postage. :)

    Trevor.
     
    Trevor, Feb 8, 2012
    #27
  8. Wrong.

    3D microlens v's 2D flat film surface. A tennis ball has the same cross
    section no matter what angle you view it from, while a flat sheet of
    film has a cross section that is cos^2. Any 3D view of the microlens
    means less than cos^4 fall-off. Also, if the "image" from the
    micro-lens is smaller than the sensitive area of the pixel, the
    illumination fall-off on a digital sensor will *always* be less than
    film - by 2 of those four cosines!

    Try measuring it, its not that difficult but too many folk would prefer
    to regurgitate the dogma than find out the truth for themselves!
    Alternatively, google my measurements from 5 or 6 years ago where this
    was discussed to death - the Olympus dogma death!

    The Olympus "telecentric" argument was just an excuse for selling tiny
    cheap chips. Nothing wrong with that - there is a huge market for
    cheaper cameras - but they lost all credibility by trying to justify an
    economic argument with fake science.
     
    Kennedy McEwen, Feb 8, 2012
    #28
  9. Bruce

    Bruce Guest


    You're welcome. But I didn't add anything that wasn't already in the
    post you decided not to read. ;-)
     
    Bruce, Feb 8, 2012
    #29
  10. Bruce

    Rol_Lei Nut Guest

    I have a Panasonic M43 and use *lots* of made for film lenses on it
    (M42, Zeiss, Leica both M & R, M39 & others).

    Some lenses, especially fast one, often don't work well at their faster
    apertures (by "not well" I mean visibly less well than on a film camera).
    It's hard to predict which will do well and which won't: a 85mm 1.4 only
    gets good at 2.8 whereas a 35mm 1.4 is very good wide open. Also,
    rangefinder lenses don't necessarily do worse than SLR lenses, just as
    telephoto lenses (like the 85mm I mentioned) don't always do well.

    But my definite conclusion is that, many lenses (perhaps as much as 50%)
    *don't* work as well on a M43 sensor as they do on film. So there is
    something going on... ;-)
     
    Rol_Lei Nut, Feb 8, 2012
    #30
  11. Bruce

    Pete A Guest

    Half a tennis ball clearly reduces its cross section as the angle moves
    away from perpendicular.
    That is simply trading pixel sensitivity for pixel vignetting. There's
    a nice illustration on page 44 of the Leica M-Sytem Catalog (page 23 of
    the PDF):

    Most (D)SLRs work adequately with most lenses because the lens mount to
    sensor/film distance is relatively large. This requires wide-angle
    lenses to be retrofocus designs, which is also, in effect, performing
    the function of your tennis ball analogy. Indeed, a retrofocus
    wide-angle shows less light falloff with both film and digital.

    As an example, cos^4 of 33 degrees is 0.49, which is 1 f-stop of light
    falloff. Many lenses suffer more than 1-stop of corner vignetting (when
    wide-open) and this is generally considered to be acceptable. Reducing
    the angle to, say, 15 degrees reduces the falloff to 13%, which is a
    negligible 0.2 f-stop.
    What they forgot to mention was that telecentric lenses are much more
    affected by dust on the rear element :)
     
    Pete A, Feb 8, 2012
    #31
  12. Bruce

    nospam Guest

    the issue is nowhere near as bad as olympus would like you to believe,
    and many lenses already were telecentric anyway.
    maybe if there aren't microlenses, but just about every sensor in the
    last decade has microlenses so it's a non-issue.
    old lenses are actually quite good, and the ones that aren't good are
    because they were not very good to begin with, not because of digital.
    some of them were telecentric, which blows the entire theory to bits.

    isn't it strange how old nikon and pentax lenses work just fine and
    produce terrific results, so much so that some of those old lenses are
    actively sought after and prices are now much higher than they used to
    be. even canon users like old nikon lenses (they can't use old canon
    lenses due to the change in the mount).

    that means that either the old olympus lenses were junk or that this
    'theory' is a total crock. anyone who used old olympus lenses knows
    they weren't junk, which leaves only one other possibility.
    olympus released a lot of bullshit about digital lenses that sounds
    good on the surface but is nothing but bullshit.
     
    nospam, Feb 8, 2012
    #32
  13. Bruce

    nospam Guest

    it was a clever ad campaign that sounds good at first, but with a
    little scrutiny, it's obvious it's bullshit.
     
    nospam, Feb 8, 2012
    #33
  14. By less than a flat sheet, and 3/4 of a tennis ball reduces even less.
    Hence a microlensed sensor will usually have less fall-off than film.
    No it isn't. The purpose of those microlenses is to put the light from
    the total pixel area into the sensitive area - having a smaller
    sensitive area doesn't change the sensitivity of the pixel, although it
    can result in lower saturation levels. Similarly, vignetting.
    A nice illustration that address a different issue, not this one. That
    is showing what Leica have done to reduce light fall off even further
    with very fast lenses.
    And the *measured* sensitivity for 40deg incidence on a Canon 5D sensor
    was as much as 94.5% of the response at perpendicular, using linear
    processing of RAW data. That's a little less than 0.2 stops - and a lot
    less than cos^4, which film would be expected to approximate.
    Many lenses do indeed suffer corner vignetting - they do so
    independently of the sensor and this is in addition to any cos^4 or
    other terms due to the sensor.
     
    Kennedy McEwen, Feb 8, 2012
    #34
  15. Most lenses will exhibit vignetting when wide open. That has nothing
    whatsoever to do with the sensor, whether digital or film, but due to
    the exit pupil being truncated. You can see this happening just by
    looking through the lens while tilting it - that circular aperture wide
    open closes down to a "cat's eye" when significantly off axis. The
    "cat's eye" is the main cause of the corner vignette. Stop the lens
    down a little and tilting it has no effect on the aperture.

    This was just the same with film as it is on a digital sensor - whether
    you noticed it or not. Furthermore, stopping the lens down doesn't
    change its telecentricity - so the very fact that you get a different
    level of vignette fully open demonstrates that telecentricity isn't the
    issue that Olympus claim(ed) it to be.

    Lots of compact, allegedly useless on digital because they aren't
    telecentric, OM lenses are used on Canon and other FF digital cameras
    without problem, hence their used prices are holding up quite well.

    Only this morning I was shooting with the Zuiko 18mm f/3.5, one of the
    least telecentric lenses on the OM lineup due to the tiny rear pupil,
    and it is extremely flat to the corners when stopped down to f/5.6 -
    less than quarter a stop. Even fully open, it is only a stop down in
    the corners - but I can see that looking through the lens, irrespective
    of the sensor, since half the exit pupil is vignetted - nothing to do
    with telecentricity. What I dislike about the Zuiko 18mm was the use of
    an even number (6) of aperture blades, resulting in coarse specular
    reflections and poor bokeh.
     
    Kennedy McEwen, Feb 8, 2012
    #35
  16. Bruce

    Rol_Lei Nut Guest


    Wow! Speaking about ranting and a condescending attitude!

    1) I never mentioned vignetting, as vignetting per se usually wasn't an
    issue when I used film lenses on my M43.

    2) At least on that particular M43 sensor and camera, the "bad" lenses
    at the "bad" apertures gave much softer images than on film, exposure
    errors (sometimes) and a general look as if they were badly flared (no,
    they were not subjected to any backlighting which would cause that, at
    least on film).

    3) I have (quite) a bit of experience with lens testing and I had
    rigorously tested all the lenses used on film.

    4) You cannot compare different sensors to each other (or to film): each
    will have a different behaviour with "difficult" lenses.

    5) Maybe actually read people's posts more carefully....
     
    Rol_Lei Nut, Feb 8, 2012
    #36
  17. Bruce

    Pete A Guest

    Yeah right - adjacent lenses will not cast shadows just as eggs in an
    egg tray are each visible from all angles. Last time I checked, they
    weren't.

    To me, this makes sense:

    <http://www.olympus.co.uk/consumer/21693_7045.htm>

    Surely, if what you are claiming is correct then film with a rough
    surface will show less light falloff with angle than one with a smooth
    surface.
    If the micro-lenses are so small that they do not shadow each other
    then they are far too small to receive the full illuminance i.e. the
    available photons per unit area. Lenses do not magically amplify the
    number of photons per unit area.
    Well, slow lenses and stopped-down lenses have a low angle of incidence
    so there isn't a problem in the first place. So, what precisely is the
    issue you are talking about?
    Just goes to show that my D700 is a total pile of crap compared to a 5D.
    Of course, and these other limitations will be clearly revealed in the
    lens bokeh.

    "Near telecentric" does not mean "telecentric". It just means that
    retrofocus (more precisely, reverse telephoto) is a lens design issue
    that must be considered for small area pixels/sensels. The problem is
    exacerbated by the fact that the depth of a pixel cannot be scaled: the
    depth determines the probability of a photon being detected in the
    material used for detection. As pixel area reduces, the depth must be
    maintained therefore "tunnel vision" increases - the angle of
    acceptance reduces. It is right and proper that small high-resolution
    sensors have lenses designed with this factor in mind. It seems to me
    that Olympus took a very bold step by attempting to define a standard
    for competitors to follow. Third party lenses (and editing software)
    for Nikon and Canon have to be created by reverse engineering, which
    isn't exactly what the consumer wants.

    I have no wish to dispel your convictions or discredit your
    measurements. Quite the reverse - let's all enjoy photography despite
    the endless marketing bullshit that surrounds it. Great photos usually
    result from being in the right place at the right time rather than
    debating the laws of physics and optics. Knowledge helps - yep, I've
    ruined many a shot by choosing the wrong aperture and many more shots
    by failing to pack the most suitable lenses for the subject. Hindsight
    can be both a blessing and a curse.
     
    Pete A, Feb 8, 2012
    #37
  18. Bruce

    Pete A Guest

    If a lens is rear telecentric then its rays are parallel i.e. the angle
    of incidence is zero. Stopping it down cannot reduce the angle of
    incidence any further. For a non-telecentric lens, of course stopping
    it down reduces the angle of incidence thereby making it _nearer to_
    rear telecentric than when it is wide-open.
    Hang on a minute - a tiny rear exit pupil ensures that rays will not
    strike the sensor/film at an oblique angle, therefore how can it be one
    of the least telecentric lenses in the OM lineup?
     
    Pete A, Feb 8, 2012
    #38
  19. But they *are* better than a flat surface, which is what matters in this
    discussion.
    Top some extent it does, but several features are exaggerated to sell
    the Olympus myth. However, the edge of field example shows precisely
    the effect I explained above - a reduction of the cosine law due to the
    spherical surface of the microlens.
    Yes. If only there were any *films* with rough surfaces.

    That isn't true. It isn't the size of the microlenses that matters, it
    is their aspect ratio. ie. height to pitch. (As shown on the same
    Olympus page you referenced above!) Of course, the retention of angular
    response due to the microlenses eventually falls off, with the response
    being much worse than a flat surface at extreme angles of incidence.
    However such angles would only occur with lenses of very short focal
    lengths and backworking distances - the tiny 4-turds sensor with its
    consequential x2 focal length factor makes the problem worse!
    Not so. Slow and stopped down lenses have peripheral rays with a lower
    spread of angles around the principle ray than fast lenses wide open,
    however that has nothing to do with the angle of the principle rays
    themselves. Telecentric lenses have principle rays with zero angle of
    incidence (perpendicular to the focal plane), the greater the angle of
    the principle ray at the corner of the image the less telecentric the
    lens is. Stopping a non-telecentric lens down increases the angle of
    incidence of exactly as many peripheral rays at the corner of the image
    as it decreases - the effect cancel out in all but ridiculously extreme
    conditions which cannot be achieved in any 35mm SLR design.
    The angle of incidence of the principle rays to each point in the image
    - departure from telecentricity, the great Satan that Olympus would have
    you believe corrupts all large sensors.

    I have no objective measurements of a D700, let alone yours, but
    subjectively it doesn't look any worse. Having said that, the 5DII has
    slightly more angular light fall off - but still less than flat film.
    I didn't claim it was. The fact is that many lenses in Olympus 4-turds
    range are no more telecentric than their OM equivalents despite the
    smaller sensor size. Whether near telecentric or less telecentric is
    all relative to sensor size.
     
    Kennedy McEwen, Feb 8, 2012
    #39
  20. How can an image form with parallel rays? It is the *principle* rays
    which are parallel in a telecentric lens, not all the rays and certainly
    not the peripheral rays which determine the f/#.

    If what you claimed was true then any pinhole lens would be telecentric
    - which is certainly not the case.
    Stopping a non-telecentric lens down does not change the angle of
    incidence of the principle rays to any point on the focal plane. Thus,
    by definition, stopping a lens down does *NOT* make a lens "nearer to"
    telecentric in any way.
    Only close to the optic axis, ie. in the centre of the frame. A tiny
    exit pupil ensures that the principle rays at the corner of the frame
    strike the focal plane at a *much* more oblique angle than those at the
    centre of the frame. To be telecentric, the principle rays for each
    image point in the frame are parallel - a small rear element, only
    slightly larger than the on-axis pupil, ensures that they are not.
    That paradox in your theory is something for you to ponder. There is no
    paradox in mine.

    One of the benefits of telecentricity is that geometric distortion is
    minimised and objects remain the same size as the focus travels through
    them. The design of the OM series Zuiko 18mm maximises both of these
    effects, the object field magnifies at close focus and shrinks as focus
    moves to infinity. Exaggerated geometry, not to be confused with the
    exaggerated perspective due to the short focal length, was a selling
    feature of that lens - achieved by its extremely non-telecentric design.
     
    Kennedy McEwen, Feb 8, 2012
    #40
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