Jeff Drew , Dec 30, 2000; 02:15 a.m.
You seem to be connecting pieces of pertinent info into a confusing conclusion. Was the 20 minute exposure taken with your gear and ISO 100 film? I rarely have seen reciprocity issues at 1/8 or slower with 35mm ISO100 print film, unless we are talking real long exposures here. The 20 minute exposure possibly did account for reciprocity failure, but are we comparing "apples to apples?" Check Kodak.com for film specs and reciprocity compensation for each film - that may help.