Cs6 slides do not clear (very dark)

Discussion in 'Film and Processing' started by KrisK_, Nov 6, 2020.

  1. Also, the 400X seems to be an intentional high contrast to make the colors brighter.

    Seems strange to me, but some like that.
     
  2. Afraid not. Those are all the Ektachrome curves that I could find. Film datasheets seem thin on the ground these days.

    Anyway, the non-push curves definitely won't be any faster, will they?

    What those curves really show is that a good scan from Ektachrome 200 could easily be made to look exactly like the Ektachrome '1600' pro - simply by manipulating its curve(s) in any decent image editor. Because it's the steepness of the curve that fakes extra sensitivity.

    On those graphs, every 0.3 step left on the X axis represents one stop less exposure. So an exposure of -2.3 log Lux-seconds on the pushed 1600 curve gets us a 'brightness' of about 1.8D. Whereas on the E200 curve it only gets us about 2.8D (10x darker), but that's starting from two very different Dmax points. The average of the 3 curves start about 0.7D (5x) apart to begin with. So in real terms there's only about one stop in density difference between the 200 ISO film and the so-called 1600 ISO film for the same exposure.

    In short, using a film designed to be 'pushed' and 'pushing' it to the max, gains you all of one stop in apparent sensitivity, but loses you about 3.5 stops of tonal range and a great deal of colour accuracy, compared to a native 200 ISO film. And you could get a better result by scanning the 200 ISO film and simply boosting its contrast in an image editor!
    The contrast isn't that much higher than the E200. The X axis scale has been squashed, compared to the other two graphs, for some reason.
     
    Last edited: Jun 11, 2021
  3. Oh, I missed the scale changed. But the X in 400X is supposed to be something like Xtra color, or more color contrast.

    But also, in the case of negatives you can make adjustments when you print. So, even if the whole image is on the bottom of the curve, (underexposed), or on the top, you can still print it (or scan it). But slides are supposed to be viewed, usually projected. If it is dark, the image might be in there, but you will have a hard time seeing it.

    And overexposed, it is usually gone.

    In any case, the 800 and 1600 Ektachromes are designed for the longer development time, independent of the ISO value that they give.
     
  4. Maybe, but the low density and high printing contrast make dust, micro-dirt, gelatin striations and grain far more visible.

    What overdevelopment (AKA 'pushing') of a negative gets you is a stronger image that supresses the inevitable dust, micro-dirt and gelatin undulations. And that's all.
    It definitely doesn't make the film any more sensitive to light.

    The same isn't true of reversal material, where the shadows get less dense the more you 'push'.

    Take another look at that Ektachrome 200 graph. The shadow sensitivity extends just as far (-3.0 log/ 0.001linear Lux-seconds) as the EI 1600 pushed film. Meaning there's no reason why a good scan couldn't be digitally enhanced to reveal just as much shadow detail as the push-processed rubbish that purports to be 3 stops faster.
     
  5. Yes, but at the time these films were designed, and mostly used, scanning was not so common.

    What mattered was viewing with a projector, and three stops underexposed make that pretty hard.

    Years ago, I had a roll of Ektachrome 800/1600 (different from the 1600), which I saved for a long time
    Then we went on a tour of Shasta Caverns:

    Lake Shasta Caverns National Natural Landmark | Lakehead, CA

    where I used it. They have lights, but are still pretty dark, so good for high ASA film.
    (Maybe about the time as ISO.) I will have to find them and scan them, but I was pretty
    happy with the results. But also, caves look good dark, and not so good bright.
     
  6. That was then, this is now. And most film shot these days is destined for scanning, only to end up as a digital file that could have been got cheaper, quicker and easier with a digital camera!

    The point is that the so-called 1600 EI film is no such thing. The -3.0 log Lux-second (0.001 Lux-seconds) barrier isn't broken at all.
    Taking the B&W film ISO rating specification as a guide, the darkest parts of the curve would have to start curving downwards at -3.3 log Lux-seconds for 1600 ISO to be acheived. That's clearly not the case, and the real ISO rating of that film is only around 400, maybe a little higher if we're really generous.
     
    Last edited: Jun 14, 2021
  7. As far as I know, the ISO rules are different for reversal films, and I at least sort-of
    understand the reasons for the rules for negative film. Among others, normally
    you don't use all of the curve for negatives, where you do for reversal.

    Looking at the middle of the curve, which is where most actual parts of
    scenes are, the 1600 is a little more negative, maybe 1 to 1.5 stops
    compared to the 400x.

    The 1600 curves are still going up at -3.0, so it seems that they should have
    kept the graph going to -4.0.

    In any case, if you want to use film for scanning, it should be negative film.
     
  8. Indeed they are, but since the ISO want to keep that methodology 'secret' unless you pay them an exhorbitant 58 Swiss Francs (and the ISO rigorously scan the web for infringement of 'copyright'), then those standards may as well not exist.

    I thought standards existed for everyone's general benefit - not to line the pockets of a bunch of Swiss gnomes - but there you go. That's the modern world.
     
  9. But the RGB density curves have already vastly separated at -3.0 Log lux-seconds, and the slopes at that point are almost identical to those of Ektachrome 200. So is it ISO 200, or EI 1600? Because there really doesn't seem to be much difference in the shadow density change.
     
    Last edited: Jun 15, 2021
  10. In the cases of the Fortran and C standard, yes, you have to pay for the official standard. But the last of the draft standard, just before the final vote, seems to be free.

    If you are selling an actual product, you can't base it on an unofficial version of the standard.

    And even though the negative standard is also not free, we know it close enough.
    (I forget the exact numbers, though.)

    I don't remember the exact rule, but many of the Ethernet standards are also free.

    There is a process for getting a free (for personal use) copy of the US national electrical code.
    When you download it, it sends a watermarked copy with your name and email address on it.
    If you distribute it, they will know it was you.
     
  11. I've started a new thread on the subject of digital 'push processing' Glen. Since I think it deserves a space of its own.
     
    glen_h likes this.

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