i have been looking at a number of threads regarding xtol developer as most people seem to think it is very good. however two things that i dont understand about film developing keep coming up. one is that different dilutions affect the acutance....what does that mean? and secondly that dilution (i think it was dilution) affects film speed.....how and why would you do that. thanks in advance.

-- Moiz Abdulkader (moiz.a@breathemail.net), September 18, 2001

Answers

Sharpness: A perceived quality of an image that is associated with the abruptness of change of tone at the edge of an object or tonal area.

Contrast: The variation between two or more parts of an object or image with respect to any of various attributes such as luminance, density, color, or size.

Acutance: A numerical value that correlates to some extent with subjective image sharpness. The term "acutance" is generally reserved for photographic edge sharpness as measured with images formed in light-sensitive materials. as distinct from optical images. Acutance is determined by printing a sharp knife-edge in contact with the material being tested using a point source of light or a collimated beam. Scatter of the exposing light in the emulsion layer causes the developed image of the knife to be diffused producing an s-shaped density distribution. Acutance is the geometrical average of the slopes at different points on the edge trace divided by the density difference between the limits of the trace.

--Focal Encyclopedia of Photography

-- Ed Buffaloe (edb@unblinkingeye.com), September 19, 2001.