Changing Film ISO

Discussion in 'Talk About Techniques' started by Ian-Barber, Feb 11, 2017.

  1. Ian-Barber

    Ian-Barber Administrator Staff Member

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    Scenario

    Let's say that the film has a box speed of 100 ISO and you have determined that your personal EI is ISO 50.

    Setting the spot meter to the box speed (ISO 100) & pointing it at say a grey card in even light will give you an exposure reading for Zone V

    Now... if you was to set the spot meter to your personal EI and point the meter at the same grey card in the same lighting, would this now give you an exposure reading for Zone V or Zone VI
     
  2. Stephen Batey

    Stephen Batey Well-Known Member

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    If you've found that you need to halve the film's rated speed to achieve the negative density you want with your equipment and technique, then by definition you'd use this value for your metering. So if your meter gives a reading that would produce a Zone V density for whichever area you've directed it at, using your modified EI should give you a Zone V density.

    I can see that's not quite that straightforward - at least, I can see reasons that might make it not quite true. But close enough for all practical purposes.
     
  3. Ian-Barber

    Ian-Barber Administrator Staff Member

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    Thanks Stephen, this is what I thought but just needed clarification. Although I am unable to test with a densitometer for 0.1 above fb+fog, I am finding that 1/2 box speed is giving me more tonal separation at the bottom end (ZII - ZIII)
     

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