Photo Engineer
Subscriber
Just to help a bit, I have dug up the following from memories of product design and the EK web site.......
The goal of most modern film design is to achieve a straight mid portion to the characteristic curve, not a bow. Old films were often bowed upwards or downwards in the mid scale which required careful placement of the exposure or the apparent contrast of the final image would vary with over or under exposures or would vary within a scene from highlight to shadows.
The purpose of having the longest straight line characteristic curve above the toe and below the shoulder (if any) is to give the most latitude with constant contrast so that detail does not suffer.
Here are the curves for 5 films from Kodak. The curves in these files show the optimum development time among many (for B&W) hidden in the many curves on each graph. The straightest curve with a contrast between 6 and 7 is the most optimum.
You can use the color films or the BW 400 CN for reference purposes. Use the bottom (cyan) curve if you are not familiar with the color masking. This bottom curve, with the lowest Dmin is the general aim of B&W films with optimum development time and is the defining curve of all color films.
T-Max 400 characteristic curves
http://www.kodak.com/global/en/professional/support/techPubs/f4043/f4043.pdf
Tri-X 400
http://www.kodak.com/global/en/professional/support/techPubs/f4017/f4017.pdf
BW 400 CN
http://www.kodak.com/global/en/professional/support/techPubs/f4036/f4036.pdf
Plus X
http://www.kodak.com/global/en/professional/support/techPubs/f4018/f4018.pdf
Portra color films
http://www.kodak.com/global/en/professional/support/techPubs/e4040/e4040.pdf
T-Grains have made this design goal more achievable with better speed, grain and sharpness.
Today's films are better.
PE
The goal of most modern film design is to achieve a straight mid portion to the characteristic curve, not a bow. Old films were often bowed upwards or downwards in the mid scale which required careful placement of the exposure or the apparent contrast of the final image would vary with over or under exposures or would vary within a scene from highlight to shadows.
The purpose of having the longest straight line characteristic curve above the toe and below the shoulder (if any) is to give the most latitude with constant contrast so that detail does not suffer.
Here are the curves for 5 films from Kodak. The curves in these files show the optimum development time among many (for B&W) hidden in the many curves on each graph. The straightest curve with a contrast between 6 and 7 is the most optimum.
You can use the color films or the BW 400 CN for reference purposes. Use the bottom (cyan) curve if you are not familiar with the color masking. This bottom curve, with the lowest Dmin is the general aim of B&W films with optimum development time and is the defining curve of all color films.
T-Max 400 characteristic curves
http://www.kodak.com/global/en/professional/support/techPubs/f4043/f4043.pdf
Tri-X 400
http://www.kodak.com/global/en/professional/support/techPubs/f4017/f4017.pdf
BW 400 CN
http://www.kodak.com/global/en/professional/support/techPubs/f4036/f4036.pdf
Plus X
http://www.kodak.com/global/en/professional/support/techPubs/f4018/f4018.pdf
Portra color films
http://www.kodak.com/global/en/professional/support/techPubs/e4040/e4040.pdf
T-Grains have made this design goal more achievable with better speed, grain and sharpness.
Today's films are better.
PE