Interpreting Densitometer Readings

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Silverpixels5

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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!
 

Thilo Schmid

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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.
 
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Silverpixels5

Silverpixels5

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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....
 
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Silverpixels5

Silverpixels5

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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?
 

Thilo Schmid

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Silverpixels5 said:
So this means I need to increase my development time in order to get my Zone VIII exposure to about a 1.3, correct?

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.
 
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