Speed gain or loss with developer

[Bill Burk]

Your Refrema example is so clear and answered exactly what the OP originally asked. How can you lose a stop of speed just by changing developer?

The surprise in your example... a "more active" developer reduced speed. The reason makes sense once you explain that you had to take the film out before the highlights blocked up, but the shadows had not had a chance to emerge.

 

[Stephen Benskin]

Attached are two papers on contrast determination. The scientific paper on Contrast Index published in Photographic Science and Engineering, and a nice little comparison of different methods published in the British Journal of Photography, "Contrast Measurement of Black and White Negative Materials."

 

[daveandiputra]

Wow, I'm going to read all the threads real slow to really understand it this is very advance for me. thanks to Steven and others for the input and contribution.