I recall once having my 50mm and 135mm for my Praktica LTL both in for service for 6 or 8 weeks, leaving me with a 28mm and a 200mm. Since I shot almost exclusively on Plus X, souped in D76, and printed on Ilford fiber paper I sort of did the experiment for a month or two. I was surprised and pleased with the some what higher percentage of "keepers" than when I had the full complement of glass.