Mapping Matters

We have started utilizing digital camera imagery taken by Intergraph DMC II 140 and Microsoft UltraCamX with GSD ranging from 5cm to 15cm to produce mapping products. On one set of imagery flown with DMC II 140 digital sensor with 14 cm GSD, the photo scale was reported to be 1:19,921 (when the mean terrain height for the project was 750 ft and the flight height was 6,800 ft ASL) as compared to a scale of 1:7,200 if I used a standard aerial film camera. Is there a reference chart or formula that will allow me to relate the GSD at a certain flight height to a film-based cameras photo scale? What would be the formula to compute the accuracies of the certain GSD for allowable contour interval generations to meet ASPRS Class 1 Accuracy Standards? We typically scan the film at 16 microns for mapping only projects and 12 microns for orthophoto/mapping projects. I realize that each of the digital sensors has unique parameters, so there may not be a global formula.