Quote:
Originally Posted by Sean  comments from the previous article system:
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By jstraw - 10:00 PM, 09-15-2006 Rating: None
I love your formulas but I find I struggle to make the clear to myself. I can't be on the right track with this one.
Tri-X at 60 seconds:
.17(Ff) * 60(seconds) ^ 1.62 = 43.04 + 60(seconds) = 103.4(seconds)
My 3 charts say 480 seconds, 600 seconds and 832 seconds (this big discrepancy is why I want a new handle on this problem).
Where am I losing my grip on your formula? |
Exponentiation has higher precedence than multiplication. Using substitution, the complete formula for calculating the exposure time is as follows:
T = Tm + Tc
Tc = a * Tm^1.62
T = Tm + ( a * Tm^1.62 )
using your example above, we get the following:
T = 60 + ( 0.17 * 60^1.62 )
T = 60 + 0.17 * 759.64
T = 60 + 129.14
T = 189.14
which is more in line with the numbers you were expecting, although certainly less than the published numbers.
Here are the calculations for the four films, using the factors published above:
TXP TMX HP5+ Delta
1 1.17 1.07 1.11 1.05
2 2.52 2.22 2.34 2.15
3 4.01 3.41 3.65 3.30
4 5.61 4.66 5.04 4.47
5 7.31 5.95 6.49 5.68
6 9.10 7.28 8.00 6.91
7 10.98 8.64 9.57 8.17
8 12.94 10.03 11.19 9.45
9 14.97 11.46 12.87 10.76
10 17.09 12.92 14.59 12.08
60 189.14 113.17 143.56 97.98
The formatting is a bit hard to read, but if you import the data into a spreadsheet, it'll be readable.