Interpreting Densitometer Readings

Discussion in 'Miscellaneous Equipment' started by Silverpixels5, Jul 23, 2003.

  1. Silverpixels5

    Silverpixels5 Member

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    I did a speed test on APX 100 in Rodinal 1:50, then took the film to the local lab to get denisity readings for each shot. I was in a rush to get back here to work so I didn't have time to ask him about the numbers. The readings are whole numbers, and I would think I would just have to take the base 10 log of each, and subtract out the FB+fog, to get the density, but it seems like my numbers are a bit high. Here's the numbers I got from the lab:

    Zone 1: 18
    Zone 0.5: 14
    Zone 1.5 : 22
    Zone 2: 27
    Zone 8: 99
    Zone 7.5: 89
    Zone 8.5 : 108
    Zone 9: 130
    Zone 0: 9

    Any help in this would be greatly appreciated. Thanks!
     
  2. Thilo Schmid

    Thilo Schmid Member

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    You must divide the numbers by 100 to get logD readings. The zone 0 reading states film base and fog density. If this reading is omitted, the FB+fog is usually already subtracted.
     
  3. Silverpixels5

    Silverpixels5 Member

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    Thanks! Everything works out great now, plus I feel pretty stupid. I'll put this college degree to use one of these days...lol....
     
  4. Silverpixels5

    Silverpixels5 Member

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    Ok if i'm interpreting this correctly then my film speed of 100 is about right with a Zone 1 density of 0.09, but my Zone VIII exposure is too low with a reading of 0.9. So this means I need to increase my development time in order to get my Zone VIII exposure to about a 1.3, correct?
     
  5. Thilo Schmid

    Thilo Schmid Member

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    That's correct. Whether 1.3logD is good for Zone VIII depends on your enlarger head. The densitometer readings are taken with a diffuse light source. If you use a condensor head, 1.1-1.2 logD would be more apropriate for a Zone VIII.
     
  6. Silverpixels5

    Silverpixels5 Member

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    Thanks for that bit of info, because I do use a condenser head!