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What is 35mm worth in MegaPixels

Discussion in 'Everything Film' started by alexham36, Sep 8, 2005.

  1. alexham36

    alexham36 Well-Known Member

    Hi, Guys,

    Has anyone worked out what is 35mm equivalent in Mega Pixels with, say, 100ASA negative film? I have been doing some calculations and to get top quality 12"x16" print at 300ppi I would need 17.3 MP digital camera and to get one of those would cost me in the region of £5K.

    Is that right or am I dreaming?
  2. Benchista

    Benchista Which Tyler

    Don't even worry yourself about it. There are many who say you need 35 megapixels, there are many who say that 6 MP is already there. One thing's for sure, and that's that you can't do a straight calculation, as there are an enormous number of factors involved. Suffice it to say that I can get a pretty reasonable (to me!) A3+ print from my 6MP EOS 10D, but not at 300ppi, but that assuming tripod use at the time of taking the picture, I would expect film and a chemical print to have more resolution - although that doesn't necessarily mean the film shot would actually look better.
  3. huwevans

    huwevans Not Really Here

    There is no way of defining an 'equivalence', though that doesn't stop people trying. It's certainly possible to show that one or the other resolves or does not resolve some given level of detail, but the big problem is that the two different media behave differently in the limit. You might prefer the digital look, or you might not.

    If you want to print 12"x16" @ 300ppi then sure enough you need 17MP. But that's just elementary arithmetic - it says nothing about how that image compares with the corresponding one taken on 35mm film. Some people would feel that 12"x16" is comfortably beyond the limit for 'top quality' enlargement of 35mm film.

    It's all really down to your own personal tastes and perceptions.
  4. huwevans

    huwevans Not Really Here

    Oh - snap! :)
  5. Benchista

    Benchista Which Tyler

    Quite! :)
  6. GeoffR

    GeoffR Well-Known Member

    Two things to consider, how far away will the viewre be from the finished picture? You can have a huge digital image,12 x 8 feet if you view it from 20 yards and it can look great. At 3 feet it will be dreadful.

    Second, because digital pixels are regular their appearance is more offensive than irregular grain, I suspect because the pixels are predictable where as grain is not.

    For a given viewing distance film will probably give a greater enlargement than digital before grain/pixelation becomes offensive but the extent will depend on many factors, not least pixel count. You cannot however equate pixels to film so it isn't really worth trying.
  7. LenShepherd

    LenShepherd Well-Known Member

    Digital and film are chalk and cheese.

    Digital captures with more acutance so the picture looks sharper, even when it contains less detail.
    Digital also has no grain so solid blocks of colour come out more solid, which is why it is often preferred over film for CMYK magazine reproduction.

    I am not aware of a digital camera (other than the Fuji S3) under £3,000, which matches the dynamic range and exposure latitude of film.
    Whilst current 6MP DSLR's are a near resolution match for 400 ASA print film, nothing under £3,000 matches the fine detail of 100 ASA print film, and nothing yet in 24x36 or "half frame" matches the fine detail of the latest 100 ASA slide films.

    For the time being it seems to be film for the finest detail, and digital for the greatest apparent sharpness.

    Two years from now (maybe less) with better performance 20+MP will put digital in a clear lead overall for those who can afford top end digital bodies and the higher grade lenses needed to meet the new resolution standards.
  8. AJUK

    AJUK Well-Known Member

    It is also a lot to do with scaning, Has anyone ever Drum scanned Fuji Superia and or Reala 100?
  9. Woolliscroft

    Woolliscroft Well-Known Member

    For the magapixel equivalent of film, one way is to use the quoted resolution figures. As you know, film resolution is measured in line pairs per millimetre. By definition, the minimum theoretical pixel consumption on digital for a line is a band two pixels wide (one for the black and one for the white), so we can take the lines/mm figure for a specific film and declare each line to equal 2 pixels, then multiply for the neg dimension (for 35mm: 24 x 36mm). On that basis a film capable of 100 lines per mm would equate to 34.5Mp. In fact, given the noise issue, that might be a bit flattering to digital, but it makes a very rough guide.
  10. GeoffR

    GeoffR Well-Known Member

    Doing the same sum, but using line PAIRS I get 138.24MP.

    Calculation (100x2)x36=7200 Lines per frame
    2 pixels per line =14400 pixels wide
    Same calculation for the 24mm side =9600 pixels
    Multiplied together =138240000 pixels.

    I think that is right.
  11. Woolliscroft

    Woolliscroft Well-Known Member

    You are counting each line pair as a separate entity. Three lines is only two line pairs etc. You then square the error in the calculation for the two dimentions
  12. GeoffR

    GeoffR Well-Known Member

    Quite right, helps to be awake before using a computer.
  13. AJUK

    AJUK Well-Known Member

    I herd somewhere (think it was mentioned in some forum) that Provia was comparedto a 1ds Mk2 and they came to the conclusion that the digital needed about 30MP to match it, That might be BS though, but if anybody can link me to it please do.
  14. huwevans

    huwevans Not Really Here

    It's not really a valid comparison though. The resolution of film, defined in this way, is the greatest number of line pairs per millimetre that can be resolved at 5% contrast. That last bit is crucial - at 5% contrast all you have is a faintest difference between two shades of almost identical grey - barely detectable at all, in fact. But a digital sensor (leaving aside the effects of anti-aliasing filters) is theoretically capable of achieving its highest resolution at or close to 100% contrast - a huge difference.

    In practice contrast decreases from the maximum once you go above half the Nyquist frequency, but it is still generally possible to achieve much better contrast as the limit is approached than with film. The two limits are different, but also the way the media behave as their respective limits are approached is profoundly different. That's why I said above that they cannot really be compared - it's a case of apples and oranges, and the bare lpmm figures simply do not tell the whole story.

    As a broad general rule, the resolution of slow or medium speed film (as defined above) substantially exceeds that of what might be considered comparable digital sensors, but the latter often deliver higher contrast over their more limited range. Which is preferable depends on who is making the choice, and what they eventually expect to do with the image (in terms of enlargement, for example).
  15. Woolliscroft

    Woolliscroft Well-Known Member

    I agree that any comparison between totally different technologies can only be rough and you are right about the poor contrast at the limit of a film's resolution. As I said before, though, digital noise causes at least as much trouble at the limits of digital resolution, especially at faster ISO settings.
  16. farley

    farley Active Member

    FWIW, an interesting link that seems to confirm that even a humble 3 megapixel camera can be 'pretty good' when it comes to competing with film! And yes, I do have a D30! (and a D60!)
  17. huwevans

    huwevans Not Really Here

    3MP will certainly be fine for many people's purposes, but what you have to remember with virtually all of these comparisons that abound on the net is that they are actually comparing the digital camera in question with a scan, rather than directly with film. Scans themselves of course vary hugely in quality, with focus, dynamic range, shadow detail, highlight detail, colour fidelity, etc. all depending on both the design and quality of the machine, and the skill and care of the operator. And then, when all those factors have been taken into account, there's the original transparency or negative.

    Correctly handled, the resolution of practically any film on the market is a long, long way ahead of 3MP. The difference is vast.
  18. farley

    farley Active Member

    Remember, this is from 'only' a 3 megapixel camera! If we take into account any 'loss' of resolution through the film scanning process - and a top quality film at that - we must also agree that 3 megapixels also loses 'something', compared with 6 megapixels (and more)! In effect, the digital camera gave the film a head start and still won! The difference in quality (up to certain sizes) - if there is one - is not as vast as one would be led to believe! :cool:
  19. Benchista

    Benchista Which Tyler

    I thought by now the whole world was aware of the deficiencies of Reichman's test methods, particularly back then!
  20. farley

    farley Active Member

    Reichman's tests may be deficient, but what of the author of the text in the link? 3 megapixels (only) - he concurred - beat film into the ground. That's two people (and probably more, who have viewed the prints; they're on public display, after all)who are obviously not 'enlightened'! Bring on the world!

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