Clip testing For Scanning

Discussion in 'Talk About Digital Scanning' started by Ian-Barber, Aug 29, 2016.

  1. Ian-Barber

    Ian-Barber Administrator Staff Member

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    I was thinking about doing a clip test with some 5x4 film to see what the upper and lover limits are for the scanner/software combination I am using.

    Has anyone ever tried this or see any reasons as to why it should not work ?
     
  2. Stephen Batey

    Stephen Batey Well-Known Member

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    I'm not clear as to what you mean. Is the idea to see the maximum and minimum densities that you can successfully scan? A clip test to me is snipping the end off a roll of film and processing it to see what adjustments need to be made to process the film as a whole - any adjustments for contrast, exposure or colour balance.

    I assume that if you're trying to determine the limits of the scanner, a standard step wedge which used to be available from Kodak, Ilford and Agfa (to look no further) would do the trick. Ilford and Agfa ones don't seem to exist new; Kodak ones are available via Tiffen, but the Stouffer one seems as if it would be the most suitable.

    I assume that a viable alternative would be to print your own on transparency film, assuming you have access to a transmission densitometer.
     
  3. Ian-Barber

    Ian-Barber Administrator Staff Member

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    Are these step wedges you are referring to textured or smooth tones
     
  4. Stephen Batey

    Stephen Batey Well-Known Member

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    Smooth tones. You can see the Stouffer ones here. Depending on what you're trying to do, you should be able to sandwich a step wedge with a conventional negative to increase the density (or, indeed, just use a gelatine neutral density filter if all you want to know is "how great can the film's DMax be for me to still see detail"?).

    Older films data sheets used to show the characteristic curve tailing off into a shoulder, and either flattening out or dropping down again. Modern films only show the curve up to a density of about 3.0. It happens that 3.0 marks the end (as I understand it) of what can be printed in a conventional darkroom. For all I know (and for all the curves show) the DMax could be greater, and could be usefully extracted by a scanner.

    One thing that is clear from the data sheets is that the slope of curve is gentler as development is decreased - exactly as you'd expect since reducing development reduces contrast. The data sheets don't say that reducing development reduces the DMax that could be achieved if more exposure were given. Unless this is the case, reducing development simply extends the subject brightness range that can be recorded. It may be useless in a darkroom for conventional printing, because the papers (always the limiting factor) can't handle it; but scanning is a totally different matter.

    This may be well off topic, since I'm still not clear what you're trying to achieve.
     
  5. Ian-Barber

    Ian-Barber Administrator Staff Member

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    Low Values
    I adapt the Zone system for exposure that is I aim to place the low vales where texture needs to be recorded on Zone III. This seems to work pretty well for my scanner/software and so far I don't have an issue with that.

    High Values
    With the high values, what I am trying to establish is how far up the Zone scale I can expose for and still be able to record texture from the scanner.

    One we reach that upper limit of RGB (255,255,255) the scanner is unable to resolve anything, no grain nothing so no matter how much we pull the highlights back in software all we are doing is making that pure white darker with no texture.
     
  6. Stephen Batey

    Stephen Batey Well-Known Member

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    In which case, a texture screen sandwiched with a step wedge should give you the information. You'll have texture throughout the range, and should be able to see the limits directly.

    If you have a 35mm camera, you can create a step wedge substitute by making a series of exposures to give increasing density and using that. This method would have the virtue of letting you see what your standard development procedure sets as the limits, although not what the limits really are. By which I mean that it's possible that you could reach the film's DMax in 5, 8 or 16 f stops of exposure, depending on how you develop it.
     

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