Dear List,
I've been analyzing the BTZS methodology for a future article in MAGNAchrom and, being the curious kind of guy that I am, I have dug deep to understand the underlying math invovlved and can say with confidence that 95% of what Phil Davis is saying not only makes sense both mathematcially and practically, but is also very familiar to me -- for all practical purposes, BTZS is nothing more than a "profile" (to use a digital term) of a paper + film combination. Even the math is essentially the same.
In fact, I've been able to model nearly all of Phil's charts using nothing more than an Excel spreadsheet, with one exception: his EFS calculations. Try as I may, I cannot model his values using Excel (I've gotten somewhat close using competely different algorithm but not close enough for it to be considered "Phil's way"). The thing that has me suspicious is his concept of matching a "triangle" with a slope of 0.62 to obtain the best fit in order to obtain your "speed point". As I look at this sceptically, it appears to me to be an affectation derived from the days when people were manually plotting BTZS curves. I believe he invented a clever and quick way to allow people with a pair of scissors to make an approximate curve that would allow them to get "good enough" estimation of Effective Film Speed. My inability to mathematically match his calculated results leads me to consider the possibility that perhaps he is using some sort of "voodoo" mathematics to derive his EFS numbers.
For example, consider the following representative data for a base film speed of 400 and a paper ES of 1.25 (this data from Jorge):
dev t speed G SBR
15 min 475 0.92 5.5
9 min 365 0.79 6.4
6 min 285 0.70 7.3
4 min 225 0.59 8.6
3 min 200 0.51 9.9
2 min 170 0.36 14.1
I cannot for the life of me understand how Phil derives his speed numbers (and mind you I'm pretty good with a spreadsheet). Hopefully, I'm just missing something simple. Can anyone on this great list shed some light here?
Thanx!
I've been analyzing the BTZS methodology for a future article in MAGNAchrom and, being the curious kind of guy that I am, I have dug deep to understand the underlying math invovlved and can say with confidence that 95% of what Phil Davis is saying not only makes sense both mathematcially and practically, but is also very familiar to me -- for all practical purposes, BTZS is nothing more than a "profile" (to use a digital term) of a paper + film combination. Even the math is essentially the same.
In fact, I've been able to model nearly all of Phil's charts using nothing more than an Excel spreadsheet, with one exception: his EFS calculations. Try as I may, I cannot model his values using Excel (I've gotten somewhat close using competely different algorithm but not close enough for it to be considered "Phil's way"). The thing that has me suspicious is his concept of matching a "triangle" with a slope of 0.62 to obtain the best fit in order to obtain your "speed point". As I look at this sceptically, it appears to me to be an affectation derived from the days when people were manually plotting BTZS curves. I believe he invented a clever and quick way to allow people with a pair of scissors to make an approximate curve that would allow them to get "good enough" estimation of Effective Film Speed. My inability to mathematically match his calculated results leads me to consider the possibility that perhaps he is using some sort of "voodoo" mathematics to derive his EFS numbers.
For example, consider the following representative data for a base film speed of 400 and a paper ES of 1.25 (this data from Jorge):
dev t speed G SBR
15 min 475 0.92 5.5
9 min 365 0.79 6.4
6 min 285 0.70 7.3
4 min 225 0.59 8.6
3 min 200 0.51 9.9
2 min 170 0.36 14.1
I cannot for the life of me understand how Phil derives his speed numbers (and mind you I'm pretty good with a spreadsheet). Hopefully, I'm just missing something simple. Can anyone on this great list shed some light here?
Thanx!
