Digital quality (vs 35mm): Any real answers?

Discussion in 'Digital Photography' started by Toralf, Jul 22, 2004.

  1. Toralf

    Toralf Guest


    I'm still wondering about how good the image quality of modern digital
    cameras (especially SLRs) really is, in particular how it compares with
    35mm film. I've seen many articles on the subject on the Net, but few of
    them seem to give you a lot of tangible information (I want to see the
    numbers, please), and I can't help feeling that tests they refer to are
    usually done to prove a point, i.e. that digital cameras are as good as
    35mm, which is not the way you do proper research.

    To say a few words about myself, I'm working for a company that makes
    high-accuracy, large-format scanners, so I'm not particularly impressed
    when I hear e.g 6 million pixels (you need to talk about *billions* of
    pixels if I'm really going to listen), and the word "interpolation"
    leaves a bad taste in my mouth. But this also means I know that high
    resolution isn't everything, of course; parameters like geometric
    precision or signal-to-noise ratio also count a lot.

    Be that as it may, some of the questions I'd like to have answered are

    1. What is the resolution of a 35mm film anyway? I think I read
    somewhere that a colour negative is at least 3000dpi. Is that correct?
    How about black&white? (Yeah I know, a film doesn't have pixels in
    exactly the same sense as a digital image, but it *is* made up of
    discrete elements after all.)

    2. What about the print? 300dpi?

    3. I know that the most common sensors are made up of individual
    elements for the read, green and blue channels, arranged in a special
    pattern, whose data is somehow interpolated into RGB pixels. But what
    exactly does e.g. 6 megapixels mean in that context? Does it mean that
    the sensor has (just) 6 million elements, or that data from a higher
    number (like 18 or 24 million) is combined into 6 million RGB pixels?

    The same question more bluntly put: When Canon/Nikon/Pentax is talking
    about 6MP, is that just a big a lie as the one about 10MP on Sigma
    cameras? (I'm hoping not, as I think the Sigma/Foveon way of counting
    really takes the cake.)

    4. Can the inaccuracy associated with the above mentioned interpolation
    be quantified and/or measured against e.g. the error introduced by
    scanning a negative with a film-scanner? And how does it compare with
    pixel interpolation in the scanning sense?

    5. And how about those other parameters I mentioned briefly above - like
    different kinds of geometric distortions, noise, flat field bias etc.?
    Can those be compared with the ones of plain old film?

    6. And the chromic aberration effects? How serious are they these days?
    And are the full-frame sensors that are actually found in some high-end
    cameras now, in any way comparable to film in that respect?

    Well, maybe some people will say I have a somewhat critical or
    conservative attitude towards digital cameras, but I actually think you
    ought to be a bit sceptical when something "new and wonderful" comes a
    long; new technology is too often introduced for technology's own sake, IMO.

    - Toralf
    Toralf, Jul 22, 2004
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  2. Why not convince yourself (one way or the other) by comparing
    side-by-side prints (or whatever final output you like) of 35mm
    prints/scans and 6MP DSLR. I viewed some 20" X 30" prints from a 6PM
    digital, bought one, sold my film bodies and haven't regreted it. YMMV

    Dave Herzstein, Jul 22, 2004
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  3. Toralf

    nitzsche Guest

    OK, I'll take a shot at it...

    It used to be "Film is cheap,' now it's "Cameras are cheap."
    - For practical purposes, it's infinite.
    - Unless you're printing posters, it's not relevant.
    - 6.3 megapixels is 6,291,456 sensors.
    interpolation be measured
    - Film will almost always be better, but it's what the outside eyes see
    that matters.
    - That's a lens issues, not sensor/film issues
    - As far as I know, all digicams are prone to purple fringing, which is
    something you don't see on any cheap slr.

    My two cents worth.
    nitzsche, Jul 22, 2004
  4. Toralf

    MXP Guest

    All the tests I have seen where 35mm film is compared to a modern DSLR
    (6-11MP)...the DSLR pictures shows more detail and less noise than a fine
    grained film like Provia 100F. It is quite fustrating that 6MP can beat
    I know many scanners can do 4000 dpi but if most of the information is

    I still use film and it will be quite interresting to see a test where e.g.
    Provia 100F
    shows more detail than an e.g. D1X/D70 or 1Ds/300D.

    When I see my slides projected it seems strange that a 6MP DSLR can do

    MXP, Jul 22, 2004
  5. Toralf

    BeamGuy Guest

    A 2MP DSLR often does better than a 35mm camera because the depth
    of field is so much greater for the tiny focal length lens. Another thing you
    might ask is how many pixels are you actually using in your eye? If you only
    have 2MP in the area that the photo is in your visual range it no longer matters
    if there are 2 or 200MP.

    And unless you take your film to a professional photo lab the processing lab
    will likely print it out of focus anyway.

    The net result is I find even my 5 year old 2MP camera delivers sharper pictures
    than my pile of 35mm equipment does.
    BeamGuy, Jul 22, 2004
  6. It's hard to say, as the resolution limit is different from that of a
    digital sensor. Rather than a hard limit, you get less information and
    more blur and noise as you increase resolution in scanning a piece of
    It's in the ballpark. The data sheet I have for Provia 100F shows an
    MTF of 35% or so at 50 cycles/mm. That corresponds. to 100 samples/mm,
    which is 2540 dpi. You presumably know what MTF means, but for others
    who may be reading, that says that if you image a sine-wave grating
    onto this film at a frequency of 50 cycles per millimeter, you will
    get about 35% of the contrast back from the film. But then what comes
    out of the lens will be reduced in contrast from what was in the
    envirnoment, so it's on the ragged edge of what you might really hope
    to reproduce. The MTF for Ektachrome 100 Pro is right at 30% at 50
    c/mm. Kodachrome 64 is about the same, and Kodachrome 25 is about 35%.
    Well, the data sheet on Kodak Technical Pan, which is an extreme upper
    bound, has MTF at 50% at 180 c/mm or so. That's for ISO 25, developed
    in Technidol. That's Kodak Tech Pub P-255, available at
    For Plus-X, at ISO 125, Tech Pub F-4018 (at
    rates it at 50 lp/mm at 1.6:1 contrast, 125 at 1000:1 (which you
    aren't likely to reach it practice).

    So I think we can say that scanning film at more than, say, 360
    samples/mm (about 9,000 samples/inch) is pretty much useless. In most
    circumstances, 100 samples/mm or 2,540 /inch is plenty. So we're in
    the region of 9MP for a normal 24x36mm 35mm film frame.
    But they aren't spaced on a regular grid, so things look a lot different.
    Well, there are lots of variables involved there. One of the little
    secrets that the "film-only" zealots don't seem to mention is that to
    view the film, it must either be scanned, projected, or printed. I
    have heard the claim that scanning digitally loses quality, but so do
    the other two processes. How good are the optics in your enlarger or
    slide projector? How perfectly is either one focused? I really don't
    know what sort of degredation is involved, but it seems that it might
    be on the same order as through the camera optics, or worse. And lens
    MTF's usually aren't quoted beyond 40 cycles/mm! Check the Zeiss or
    Canon Web sites if you don't believe me.
    The former. Except for the Foveon sensor in the Sigma SD9/SD10, which
    has about 3.5 million sites, each of which detects all three channels.
    Not really. The reality is that sensing all channels at each location
    is a Good Thing, other factors being equal, but the color filter array
    isn't as bad as you might think. First of all, the three color
    channels aren't completely uncorrelated, so the information from a red
    sensel can be used to help estimate the red and green values at that
    point. Second, images have some sort of spatial structure, and modern
    demosaicing algorithms try to detect that to deduce missing
    values. Finally, the sampling rate is higher for the green channel, to
    which the human visual system is most sensitive, both in luminance and
    Yup. Lots of them are only being noticed now with digital sensors
    behind the same lenses that people have used for years with film.
    I suspect that it's a matter of display more than anything else;
    the magnification on screen at a 1:1 pixel magnification is huge
    for most cameras, and people can use the little eyedropper to see
    just how much the illumination falls off in the corner of the frame.
    Chromatic aberration is basically in the lens. Doesn't matter
    what sensor is behind it.
    Oh, sure. But there are a number of photographers who are putting away
    their 4.5x6 film cameras because they see better quality out of the
    Kodak DCS 14 MP cameras. In a functional way, the best digitals are
    pretty good, though their limitations are different from those of film
    Stephen H. Westin, Jul 22, 2004
  7. Not in this universe. For practical purposes, it's somewhere between
    30-75 cycles/mm, most of the time.

    Stephen H. Westin, Jul 22, 2004
  8. Well, at 40 cycles per degree, and perhaps a 140-degree horizontal
    field of view, it's over 10,000 pixels across. We don't have any
    display that can approach it.

    Stephen H. Westin, Jul 22, 2004
  9. Toralf

    Mark Weaver Guest

    I don't think there are any numbers that are going to satisfy you. First of
    all, there are the variables of the film, the scanner, and the subject (are
    you talking about a picture of a high-contrast B&W test target using slow,
    fine grain film with a prime lens and scanned with a high-end drum scanner?
    If so, that's going to yield idealized results that don't match the
    practical experiences of photographers comparing film to digital). And then
    there's the judgement call with respect to grain-- when you've reached a
    scanning resolution where additional detail can still be extracted but the
    grain of the film is obvious and objectionable--do you still count that as
    useful resolution? And if not, who decides at what point the grain is
    obtrusive enough that addtional resolution is of no value?

    Mark Weaver, Jul 22, 2004
  10. Toralf

    Zebedee Guest

    I spent ages working out all the details. I came to the conclusion that if
    you measured the area of a perfect print from a 35mm negative or 35mm slide
    in inches and then divided the dimensions by 150 you'd be able to work out
    the vertical/horizontal pixels of the image. Then simply multiply the two
    together to get megapixels. That's the theory anyway.

    In practice, how big is the biggest print you normally make? If your normal
    biggest print is 10x8 then 3 megapixels is all you ever need (two at a

    But the biggest limitation is your printer. How many of us can afford an A3
    or greater printer or even the ink to make A3 prints?

    How many A4 prints can you hang on your wall?

    I decided to settle on 3 megapixels. It's adequate for my needs and as with
    slides, I ensure my photos are perfect before I squeeze the button. I claim
    3 megapixels is the perfect equivalent of 35mm for most purposes. 6mp just
    eats up storage space for no visible advantage.



    (Claiming asylum in an attempt
    to escape paying his debts to
    Dougal and Florence)
    Zebedee, Jul 22, 2004
  11. I have 50x60 (cm) B&W photo paper which I use for the right pictures.
    I doubt 3 (or 6) megapixels will do the job...

    Chris Loffredo, Jul 22, 2004
  12. Toralf

    Zebedee Guest

    50cm = 19.7 inches
    60cm = 23.6 inches

    19.7 x 150 = 2955 pixels
    23.6 x 150 = 3540 pixels

    2955 x 3540 = 10.4607 megapixels

    It could be a little stretch for a 6mp camera or you could even use the
    Kodak 14mp SLR

    Having said that, it's a really unusual size and more suited to medium
    format than for 35mm.



    (Claiming asylum in an attempt
    to escape paying his debts to
    Dougal and Florence)
    Zebedee, Jul 22, 2004
  13. 20x24 is a pitiful joke from 35mm B&W films, even Tech Pan. If one has any
    sense of quality imaging at all, 11x14 is MF (645) territory. 20x24 from 6x7
    would be OK, but would look better if you used LF.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Jul 23, 2004
  14. Toralf

    Sabineellen Guest

    I decided to settle on 3 megapixels. It's adequate for my needs and as with
    What specific camera did you settle on? I settled on a modest but good enough
    5mp, 'cos i thought if I go for a high end 5mp then i might as well get an 8mp,
    and if i go for an 8mp then I might as well get a dSLR, and if I go for a dSLR
    I might as well have one of the better one, so it had to stop at one point.

    BTW, it's a wild claim to say that 3mp is "the perfect equivalent" of 35mm for
    most purposes. To print 8x10 at 300dpi you need 7.2 megapixels. 3mp, or even
    2mp, is good enough if you only need them displayed on a monitor. I personally
    display images on a calibrated 21" monitor and find that I really don't need
    prints. I had a home computer in the early 80s and got a PDA many years ago so
    personally I'm well adapted to the paperless existence. In fact, I really
    dislike writing and I'm quite comfortable with typing. So yes, for my usage,
    5mp, or even 2mp, would be adequate, but i wouldn't call it a "perfect
    equivalent" to 35mm.
    Sabineellen, Jul 23, 2004
  15. Toralf

    Sabineellen Guest

    Where would the dSLRs fit into this?
    Sabineellen, Jul 23, 2004
  16. Toralf

    Zebedee Guest

    Just why would anybody print at more than 150dpi when that's the maximum the
    eye can see?



    (Claiming asylum in an attempt
    to escape paying his debts to
    Dougal and Florence)
    Zebedee, Jul 23, 2004
  17. Toralf

    Paul J Gans Guest

    Because dpi is often misleading. For some older printers
    each color was printed as a separate dot. So 150 dpi meant
    that pure red, for instance, is only at 50 dpi.

    ------ Paul J. Gans
    Paul J Gans, Jul 23, 2004
  18. 'Resolution' is not all there is to it. It's the wrong question to ask
    to start with.
    Not in exactly the same way as a digital image. A photograph is made
    up of distinct grains of differing sizes and arrangements.

    All you need to know is: Digital images suck.
    Michael Scarpitti, Jul 23, 2004
  19. That's not so startling. That film is not as sharp as Kodachrome. It's
    a poor choice to compare.

    It is quite fustrating that 6MP can beat
    Michael Scarpitti, Jul 23, 2004
  20. Toralf

    Skip M Guest

    You may claim it, but that don't make it so. There is a decided difference
    between files from my Canon D30 (3mp) and my wife's 10D (6mp) cameras. 3mp
    is most definitely not the equivalent of film for anyone who is enlarging
    beyond 4x6.
    I have a Canon 9000 printer that prints photo quality A3+ prints, we both
    regularly print to that size and A4, we have about 20 16x20 inch frames
    hanging on the wall in our stairwell, alone, as we speak. I have a show
    coming up in which more than half the images need to be printed A3+. Your
    theory won't work for me, and I'll bet that in a short time, you'll realize
    that you are dissatisfied with the images you are getting utilizing that
    theory, too.
    Skip M, Jul 23, 2004
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