Tricky shot of an old church

Discussion in 'Photography' started by Scott W, Nov 16, 2005.

  1. Scott W

    Scott W Guest

    Can you show me a real-world waveform where 2x does not work? In the
    waveform I showed I can sample at 1/8 the rate as what the data is
    shown at, and still get all the info on the waveform.

    This is very simple stuff, the highest rate you need to digitize to is
    2x the highest frequency that is present in the waveform.

    Scott W, Nov 24, 2005
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  2. Sine X: sample at 0, 180, 360, ...... every 180 degrees, which is
    at 2x the frequency.
    Result: 0, 0, 0, 0, 0, 0, ....... which means you never see
    anything and can't recover anything.

    Sampling at 2x the highest frequency is not Nyquist. Nyquist
    says at least slightly more than 2x, assuming infinite
    sampling. If you don't have infinite sampling, the sampling
    rate must go up in order to not induce phase errors.

    In the case you posted of the 256 numbers, a damped sine wave,
    if you sample every 8th channel and
    you reconstruct the sine waves, you do so using an assumption.
    There are other equally valid solutions. It is non unique.
    Also, it is not a likely response function of a
    subject in an imaging system.

    Roger N. Clark (change username to rnclark), Nov 24, 2005
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  3. Scott,
    There are two other images at full resolution from the
    same 4x5 scan at:
    (3 test areas, the previous grass blades was only one).

    But I was hoping people would see "the big picture" before
    this. Look at the image again:
    The important thing about this image is as follows:

    The 4x5 image was done at f/45, the 35mm at f/11. Both
    lenses are diffraction limited. The focal length of the
    4x5 is about 4x that of the 35mm image. Thus, the angular
    resolution of the two images should be identical. 4x5
    should have no advantage in image detail. Of course every
    large format photographer knows that is false, and that
    is exactly what the images show. The 35mm image is
    very inferior concerning detail. But why? It is due
    to the film! The resolution of film for low contrast
    subjects is really pretty poor. So the loss in image
    detail going to high f/ratios is mitigated somewhat
    by the low MTF of film, even high resolution fine grained

    This is a big reason why there has been so much debate
    over film versus digital: the different MTF responses of the
    two media. Digital cameras typically have a higher MTF response
    than film, but then drop fast, whereas film keeps going,
    but low MTF. But that low MTF response still carries
    enough information to give an image the perception of
    fine detail.

    Then, to tie this back to your original post, the implications
    for large digital mosaics like you are producing, have the
    potential of showing more detail than large format, even if
    the pixel count is less. For example, some of my 4x5 scans
    are 12,000 x 16,000 pixels. I would bet an 8,000 x 10,000
    pixel digital camera mosaic would look superior (less noise,
    more apparent detail) than the 4x5 scan, even if the 4x5 was
    done at low f/stop on a perfect lens. That is because
    the film is a large part of the limitations to detail
    in an image, even 4x5 images.

    Roger N. Clark (change username to rnclark), Nov 24, 2005
  4. Scott W

    Neil Gould Guest

    Well, I understand and agree with Roger's analysis, so see his response.
    I'll go further than his comment to add that there will be errors for
    *any* phase offset and for almost any waveform sampled at 2x.

    Neil Gould, Nov 24, 2005
  5. Scott W

    Scott W Guest

    The only assumption I need make with my 1/8 th samples is that there
    are not frequencies above 1/2 my sampling rate, that is the only
    assumption, given that there is only one solution, or can you find

    Scott W, Nov 24, 2005
  6. Scott W

    Scott W Guest

    Ok lets look at the number, if an 8k x 10K digital image looks as good
    or better then a scan from a 4 x 5 camera this would say you are
    getting about 4 MP/ square inch, this is the number that I tend to use
    for film. But this is only if the film shot is done fairly well, good
    film and good optics. If you were to shoot that 4 x 5 shot at f/64 it
    would not be nearly as good. BTW in your table for comparing digital
    to film you have used numbers a bit higher then 4 MP/sq inch for a few
    films, I believe close to 7.6 MP / sq inch.

    There is no question that 35mm is way limited by the film and to get
    away from this limit you need a lot bigger film piece. It is also very
    true the if you shot f/16 on 35mm and f/64 on the 4 x 5 the 4 x 5 image
    will have a lot more detail, at f/16 on film diffraction hardly an
    issue at all, it is almost all the film. But by f/32 we are getting
    much softer then at f/16, for any size camera, at least if a very good
    film is used, still not enough to greatly reduce the resolution over
    what the film MTF is, but clearly softer. But going from f/32 to f/64
    is the killer, loosing almost half the resolution. And you know that
    you take a big hit when going to f/64, you would only shoot at f/64 if
    you had to have the DOF.

    This whole discussion started from a statement that diffraction was not
    an issue with LF cameras, in many ways it is more of an issue because
    to get good DOF requires large f numbers.

    Take a look at the sharpest part of a photo that you have taken at f/64
    and compare it to the sharpest part of one taken at f/32 and tell me
    the one at F/64 is not way softer.

    And if we move more in to the extreme, if I were to try and get the
    same shot with a 8 x 10 LF camera to get the same shot I would need to
    use a lens twice as long and with twice the f number, at f/128 I would
    not get much better of a photo shot then shooting the 4 x5 at f/64.

    Scott W, Nov 24, 2005
  7. Scott,

    The original full image for reference, 4x5, 90mm lens, f/64:

    30x40 inch, 300 ppi crops:

    Print these at 300 ppi and you will see the detail in a
    30x40-inxh print. You argued that a 30x40 inch print that the
    diffraction spot size about 80 microns in the film plane,
    so a 30x40 inch print would produce diffraction spot sizes
    of about 640 microns (8x enlargement * 80 microns),
    this about 0.64 mm. With this I agree. On a 300 ppi
    30x40 inch print that equals about 12 pixels. But the crops
    show edge transitions of about 3 pixels in the sharpest areas.
    Diffraction spot diameter does not equate to blur circle of all detail.
    You get detail up to and beyond about half the radius of the
    diffraction disk, consistent with these crops. But the crops show
    something much more important than diffraction.

    Look at sub1-30x40.300ppi.jpg: the yellow detail in the upper
    left is a little soft, the edge of the white flow petal is
    in best focus, the purple petal beyond is slightly soft again,
    and the green leaves in the background is softer yet,
    This illustrates depth of field is a more significant issue
    than f/64 diffraction. This is the flower prominent at
    bottom center in the full image.

    Now look at sub2-30x40.300ppi.jpg: This is a flower that
    is to the upper left of sub1, but still slightly below
    the center line of the image. It is a little softer due
    to the tilt used in combination with the f/64 depth of
    field. If I opened up, DOF would be more limiting.

    Now look at sub3-30x40.300ppi.jpg: This is a red flower
    to the upper right from the sub1 flower, an equal distance
    as sub 2 but right, not left. This one is softer yet because
    this flower sits in a hole and DOF becomes more of an issue.
    Yet edge transitions are still only 3 to 4 pixels.

    Grain and scattering in the film is still contributing to softness,
    even at f/64. So the loss in detail from f/32 to f/64, for example,
    is less than a factor of two.

    The point of all this is that real images tell the full story,
    whereas one can cite all the numbers one wants, but unless the
    model is complete, one might miss important factors.
    While diffraction is a factor in large format images, at
    f/32, f/45, f/64, etc., it is not the only factor, and should
    not be the only consideration in such cases. Film MTF is still
    affecting f/64 detail, as is DOF.

    Regarding your other numbers, like 4 MP per square inch of film,
    this again is putting a number that provides a VERY INCOMPLETE
    story of the image. First, megapixels is a function of film
    type and speed, so I bristle at people you cite single numbers.
    (e.g. film better than digital--yes, no, both are correct-depends
    on the situation). See:

    The above page discusses these points. For example, I rate fuji
    velvia at 10 to 16 megapixel equivalent in 35mm, or 7.5 to 12
    mpix/sq inch (12 if you want to get the color resolution),
    and TMAX 3200 at only about 2.5 megapixel equivalent.

    But resolution is not the only thing regarding image quality.
    Signal to noise and shape of the MTF response are major factors,
    as well as DOF and focus.

    The MTF shape and high signal to noise ratio is why digital capture
    can get a higher *perceived* image quality than much higher pixel
    scanned film. That is described under Apparent Image Quality (AIQ)
    on the above page.

    So when I said in a digital mosaic that had less pixel count
    than scanned 4x5 film, that the digital mosaic could look superior.
    I included signal-to-noise, f/ratios and DOF, diffraction,
    and different MTF between the two systems. Again, I did not
    focus (pun intended) on one number, but considered the whole system.

    Roger N. Clark (change username to rnclark), Nov 25, 2005
  8. Scott,
    I looked at your test data a little more closely. The period of the
    highest frequency wave is 21 samples. So your use of every 8 samples
    violates your premise of sampling at twice the frequency. Your sampling
    is 2.6 times the frequency, which, by the way is a commonly used
    sampling rate in electrical engineering. Even so,
    given an unknown function, you do not know the phase, in which case
    with only about 10 cycles, you can have different solutions.
    As your number of cycles goes down, phase errors can contribute more,
    and more solutions are possible.

    How about a real imaging example? Below is a table of numbers. The optical
    system has a Gaussian response function with a full width at half maximum
    of 2 pixels. Sampling is every 1 pixel. Derive the source(s):
    position, shape, intensity. The intensities in the table are
    8-bit linear (not gamma encoded).


    Roger N. Clark (change username to rnclark), Nov 26, 2005
  9. Scott W

    Scott W Guest

    With regards to my data, you can not determe the highest frequencies present
    by simply counting the periods of the cycles, the envelope of the waveform
    effects the bandwidth as well. If you were to look at the fourier transform
    of my signal you would see that in fact I am sampling above 2x the max
    frequency in the signal.

    I did a quick fourier transform on your data and it does not look to be
    bandwidth limited to ½ your sample rate, here is a link to what I am seeing.

    There is clearly a source of energy that is much higher in frequency then
    the main signal.

    Any mathematician looking at your data would say that it was under sampled,
    that there are frequencies at more then 1 / 2 the sampling rate.

    Scott W, Nov 26, 2005
  10. Scott W

    Scott W Guest

    So if these are 300 ppi sample then they would have be scanned at the
    equivalent resolution of 2400 ppi on the film?

    300 x 40 / 5 = 2400

    They are about as soft as many 4000 ppi scans I have seen and softer then

    I did print out the samples at 300 ppi, and whereas I am sure it is stunning
    as a 30 x 40 inch print if you were to print out a 4 x 6 section it would
    look like crap.

    If I compare your sample to this one

    they look about the same to my eye in terms of sharpness, but Bret's scan
    was done at 5400 ppi, over twice what your scan was done at.

    If I take Bret's scan and down sample it to match your it look very sharp,
    clearly your scan is not getting even close to all the detail that the film
    can produce, and this is what we would expect shooting at f/64. If Bret had
    shoot at f/64 his would look just as soft.

    If I down sample you image by a factor of two then it starts to look pretty
    sharp, but this leaves you would only 27 MP, which is not that much more
    then what someone shooting 6 x7 MF with good film can do.

    Here is one more way to look at the image, my photo of the church is only 75
    MP, I resample and cropped to get a 30 x 40 inch 300 ppi image and pasted a
    bit of this next to your crop, seen below.

    When printed out there is no comparison in sharpness between the two, but a
    sharp clean shoot from a 4 x 5 should be able to produce at least 75 MP, 100
    MP would be more like it.

    So is my comparison fair? Well no since you had to deal with a lot more DOF,
    but that is my point when you go to large f number to get the DOF you suffer
    a lot of lost detail. It may be the right trade off to make but you can
    pretend that you are not losing the detail.

    Scott W, Nov 26, 2005

  11. As A.Z. once confided to me over a Sachertorte in the Rathaus Park:

    "Although it is theoretically feasible to extend this procedure
    to more general self-adjoint boundary-value problems associated
    with nth order differential operators, in practice this does not
    always work since the existence of one single function K(x; t),
    which generates all the eigenfunctions of the problem when the
    parameter t is replaced by the eigenvalues, is not always

    I think that settles it. Move it to Hilbert space.
    Nicholas O. Lindan, Nov 26, 2005
  12. Scott W

    jet Guest

    personally ... it's the side of a church with a steeple ... granted to
    you standing there it's beautiful ... since there is little you can do
    about parking lots, cars, telephone wires and such ... I would take
    that wide angle photograph near the front steps of the church from as
    close as you can get (and as wide as you can get) ... it would be
    really great if you could get the front of the church and some part of
    the steeple in the same photograph ... I would use a 5x7 (110mm) or 6x9
    or 6x12 (37mm??) with a wide lens ... to me there may be more story
    told from the front of the church than from a side shot of the steeple
    and building with parking lot ... just a matter of choice and taste and
    that like life is unique amongst all of us ...
    jet, Nov 27, 2005
  13. Nicholas O. Lindan wrote:

    Very cute, but I thought the thread was more like:
    Many new large format photographers are enthralled with the
    detail in the image and are driven to maximize sharpness.
    But many factors influence the overall image, and
    sharpness is only one factor.

    But Scott has some good points and is illustrating
    some new methods, and hopefully both he and I and others reading
    are learning (I am). I do see Scott's point that f/64 is
    not as sharp, but I already knew that. I don't think other large
    format (4x5) photographers use f/64 unless it is needed, but
    sometimes it is needed and it is not the factor of 2 loss in
    sharpness from f/32 that some might believe. It is not
    because film MTF contributes too. I was hoping Scott would
    see the light too (perhaps he does).

    Roger N. Clark (change username to rnclark), Nov 27, 2005
  14. Scott W

    Lorem Ipsum Guest

    The utter truth is that the picture is not tricky. Not one bit. The photog
    is more concerned with technology than making a correct picture.
    Lorem Ipsum, Nov 28, 2005
  15. Scott W

    Scott W Guest

    So what do you belive is a good number for sharpness loss when going
    from f/32 to f/64, using let's say shooting with Velvia 100, assuming
    that the lens is diffraction limited at f/32 and f/64.

    And other then limitations of the film what would keep it from being a
    loss of 2?

    BTW have you seen the scans that Max Perl has done using 35mm Gigabit
    film, pretty amazing detail. It really shows how much detail a good
    scanner can get if the detail is on the film. I printed out one of his
    4000 ppi scans at 300 ppi and the sharpness is amazing.
    Here is a link to his scan.

    Scott W, Nov 28, 2005
  16. I would say that it is less than a factor of 1.5 loss on
    velvia from f/32 to f/64. The loss would be less on higher
    speed color films.

    The gigabit film is Agfaortho 25. Agfa is now bankrupt.

    The guy who does my drum scans showed me a 30x40 (approx)
    print of scanned 35mm Kodachrome 25 at 11,000 ppi (the limit
    of his scanner). It looked like a 4x5. Unfortunately,
    now days velvia is the highest resolution film.

    On Max Perl's web site, he also has velvia, and it
    looks soft in comparison.

    The film industry is going backwards---faster film, lower

    Roger N. Clark (change username to rnclark), Nov 28, 2005
  17. Scott W

    Scott W Guest

    There is no doubt that his velvia scans are much softer then the
    Gigabit scans, it does show that the scanner is pretty much not
    normally the limiting factor, at least if you have a good scanner.

    I have notice the trend for faster film for many years now, when I look
    at the shelves I don't see anything slower then ISO 400.

    As for your 1.5 factor going from f/32 to f/64, I would put it a bit
    higher but even a factor of 1.5 is going to loose over half the
    information on the film. It is interesting to note that at this loss a
    6 x 9 MF camera shooting at f/32 would capture just about the same over
    all detail as a 4 x 5 shooting at f/64.

    Scott W, Nov 28, 2005
  18. Half? 1) the remaining info is at a very low MTF, 2) if it was half,
    then there would be a factor of 2 loss, which you agreed it was not that
    much. 3) most of the information is at much lower frequencies
    (go back to your 2000 ppi test).

    Roger N. Clark (change username to rnclark), Nov 28, 2005
  19. Scott W

    Scott W Guest

    I assumed your factor of 1.5 was a linear number, was this wrong?

    It would be hard to believe you would not loose at least a factor of
    1.5 in linear resolution,
    which would be a total pixel factor of 2.25.

    At some point clearly double the f number would reduce the linear
    resolution by a factor of very close to 2. As an extreme example if we
    were to go from f/500 to f/1000 we would expect to have almost exactly
    half the linear resolution.

    So the question is at what f number to we approach this point, clearly
    the choice of film has to be taken into account. I believe that at f/32
    and higher we are in that range, clearly you thing it would take a
    higher f number.


    Scott W, Nov 28, 2005
  20. Scott W

    jet Guest

    making a "correct" picture is completely personal ... what is correct
    to you may not be to others ... personally I find the image less than
    thrilling ... but alas it is not my judgement to make ...
    jet, Nov 28, 2005
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