When I received my 75mm lens and started shooting some Fp100Cs. I noticed that the lens on and off gives me very low contrast photos, especially those taken outdoors. At first I thought it was lens flare as its the entire photo and so I was very particular about having the hood on the lens all the time.
When I received the 100mm lens, I too shot and sometimes occasionally saw the photos are a bit over exposed or low in contrast. I was really dissapointed with the results until I developed my slides and negatives. Its a total different experience! The shots on the slides and negatives were great. Very contrasty and sharp. No flares detected.
Then my 3000B arrived from the mail and I shot a few shots with the 100mm and to my horror, see light streaks all over the place. Then I felt so stupid, its not the lens that flared! Its the back! The lightseals are worned and need replacements! The higher iso 3000B actually reacts faster to even the least of light leaking into the back. So I could easily determined the previous low contrast photos were due to leaks.
I have to quickly finished the 10 shots that I loaded and performed an operation on the polaroid back. Shined my torch through the lightseals and presto. Saw the leak. Opened the back up (just held with 8 little screws) and cleaned the seal with some alcohol and replaced the foams. All done in less than 30 mins time.
Moral of the story? Check your equipment, especially those old old cameras for such issues first before blaming the lens... :P