Math question - sort of

Discussion in '35mm Cameras' started by Eric Miller, Sep 23, 2009.

  1. No it is an exact quote of your question, excluding the waffle that put
    it in context as that was already clear from the preceding thread.
    Context. The answer is NOT simply scaling pixel size of the 10D to the
    7D, which is what you were given. Without taking optical resolution
    into account the equivalent focal length you would need on the 10D
    compared to the 7D could be close to 50% higher than is in fact the
    case! Optics, even perfect optics, don't have infinite resolution! When
    the optical resolution is close to the pixel resolution then they MUST
    be taken into account to answer your question, or you end up with
    meaningless unresolved pixels. You seem to have a major problem
    understanding that.
    When you were 5 and asked your Mom where you came from, you were
    probably happy with her reply that a stork brought you. By the time you
    were 10 you would expect a better, more complete answer, to exactly the
    same question. By the time you were 15 you ought to know the full
    answer yourself. Stop behaving like a 5 year old - there is no Santa
    Claus, even if some of your friends still believe there is!
    Smart enough to know that any question I ask may well have an answer
    which is more complex than I expected and with enough common decency not
    to criticise those who make the effort to explain that.

    Carry on living in ignorance: the x1.7 scale factor given by the partial
    answer is at least 50% too high. A 400mm lens on the 7D would NOT give
    equivalent resolution to a 680mm lens on a 10D: you will be lucky to
    achieve half of that 280mm effective focal length extension depending on
    the optical resolution of the 400mm lens in question. In other words
    540mm, or less, equivalence in terms of what is actually RESOLVED.
    Kennedy McEwen, Sep 26, 2009
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  2. Eric Miller

    John Sheehy Guest

    The lenses are to blame for any optical issues with high densities. The
    higher density *NEVER* exacerbates any lens problems. Lower densities
    lower the resolution, so you see less of everything, including subject

    You position is all "talk" and "logic". You can not demonstrate what you
    believe, because it only exists in bad logic and bad paradigms.

    Here's what happens when you try to demonstrate, and go about it the
    right way:

    You shoot the same scene with the same lens, same ISO, same Av and Tv,
    and then you use a converter with no noise reduction, and upsample
    critical crops from both images to the same subject size. No matter how
    much lens fault is brought into the light with the higher density, the
    higher density still has a more accurate rendition of the subject,
    agressive sampling does not avoid lens issues; it just makes it harder to
    tell why the image has so much less real subject detail.
    John Sheehy, Sep 27, 2009
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  3. Eric Miller

    Paul Furman Guest

    Extreme microlenses can emphasize CA and even vignetting. I don't know
    if that's necessarily proportional to pixel density but it appears to be
    more of an issue.
    Paul Furman

    all google groups messages filtered due to spam
    Paul Furman, Sep 27, 2009
  4. Eric Miller

    Paul Furman Guest

    On second thought, the original question is about magnification, just
    magnification at/near infinity. FOV only matters here if the 5 inch tall
    bird goes outside the frame. Print size doesn't exactly matter either
    unless you want the result in inches instead of pixels, the only
    question is how much the bird can be enlarged.
    This is still a handy basepoint. How many pixels tall would the 5 inch
    bird be for a 7.2MP full frame 35mm camera, focused to infinity? I guess
    we need to know how far away the bird is.
    Or if you double the linear pixel count, that doubles the number also.
    So the pixel spacing is really all you need, though it's nice to nail it
    all back to that normal lens at infinity and an 8x10 print as the basepoint.

    Yeah, this is magnification, like binoculars, microscopes & telescopes
    are described as 5x, 10x, etc.

    scratch this comment:
    Lastly, the lens has resolution limits so you can say that the lens is
    only good up to a particular magnification and decide not to waste money
    on pixels beyond that point. However, the point where a lens gives up is
    variable according to many factors like how close to the edge or center,
    what aperture, subject distance/magnification, etc. The MTF charts have
    to pick a narrow definition and the nyquist lines on those have to pick
    a simple theoretical diffraction point but there is usually some
    discernible detail beyond that even if it doesn't meet the strict criteria.

    Paul Furman

    all google groups messages filtered due to spam
    Paul Furman, Sep 27, 2009
  5. Film has silver grain (analog photosites) sizes of 2um or less, the size of
    photosites on most small sensor cameras of 1/2.5 being approx. 2um. You
    will always be limited to your weakest link. If you increase the lens
    resolution you are limited to the resolution of your sensor being 4-8um in
    photosite sizes. (Luckily, in P&S cameras the optics quality and resolution
    is matched to the photosite sizes.) If you increase the pixel density
    without increasing the lens quality then all you are capturing with those
    smaller photosites are the blurry edges afforded by the lens. No gain in
    useful information. A bit like those toy telescopes that advertise 600x
    magnification on a 2" diameter objective lens. All you are doing is
    magnifying blur beyond 50x magnification with a 2" lens. Or those that put
    high-gain amplifiers on their fringe-area TV antennas to only amply noise.

    It's not an "either/or" venture. It's an "and" issue.
    You Are The Weakest Link, Sep 27, 2009
  6. Eric Miller

    John Sheehy Guest

    I meant the density itself. Of course, microlenses could be poorly
    designed. Even then, however, oversampling allows extemely easy and smooth
    correction of CA, both from the lens, and that generated by poor
    John Sheehy, Sep 28, 2009
  7. You don't know how to comprehend that increasing either does NOT include
    increasing both.

    Pray tell, if you have a sensor that can only record the absolute minimum
    of (for sake of argument) 3" of arc, how then will a lens that can resolve
    1" of arc be recorded on that sensor?

    If you have a sensor that can record 1" of arc, how then can a lens that
    can only resolve 3" of arc record 1" of arc on that sensor?

    You will always be limited by your weakest resolution link. Now if you add
    in antialiasing masks, printer limitations, and the limits of the human eye
    depending on viewing distance, then the resolution limits climbs

    You're an idiot pretend-photographer troll. Plain and simple. Proved 100%.

    You ARE the weakest link.

    <throwing a dead goat under its troll's bridge to see if it'll go feed on
    You Are The Weakest Link, Sep 28, 2009
  8. OR != XOR. Look it up. Write a logic table.

    Wolfgang Weisselberg, Sep 29, 2009
  9. Eric Miller

    Martin Brown Guest

    Although it does make it easier.
    There are resampling methods derived from radio astronomy that can
    handle this situation accurately but they are computationally expensive.
    Bilinear spline is about the cheapest half decent option found in
    standard packages. But there are better ones if you have resources to
    burn. It ends up with the law of diminishing returns so how far you push
    it is really determined by how unique or irreplaceable the image is.

    If you have the option then oversampling the measured data by about 1.5x
    the Nyquist theoretical minimum for a monochrome imaging system is
    worthwhile. Otherwise you may see obvious jaggies in the raw image.
    Beyond that you are not gaining much although for a Bayer sensor you
    still get a bit of extra chroma information out to 2x oversampled.

    Martin Brown
    Martin Brown, Oct 7, 2009
  10. Eric Miller

    Martin Brown Guest

    Actually there isn't all that much of a difference apart from the
    obvious one that a time series is one dimensional and so a lot more
    amenable to analytical techniques when sampled at equal intervals.

    Time sampled data is usually integrated over a time delta-t rather than
    a true snapshot of the signal by a flash converter at exact time t.
    Indeed, but having some of that extra data can make post processing
    deconvolution more reliable provided that you have not traded signal to

    The point here is that an undersampled digital image does present some
    difficulties for post processing to remove chromatic and other
    abberations. They are not insurmountable but it is easier with an
    oversampled image.

    Martin Brown
    Martin Brown, Oct 8, 2009
  11. Eric Miller

    Mr. Strat Guest

    Are you still using that Panasonic piece of shit? I guess it doesn't
    matter since you don't have the ability to create a decent image.
    Mr. Strat, Oct 9, 2009
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