After reading some threads that the 18-200 measures out to only 170, and not being able to find one poster who could point me to an actual test, I performed my own test. I am neither a scientist or a mechanical engineer, so my test would not stand up to the requirements of either. My test was simple. I took a number of photos at 144 or 150 (so said the data file) and then took the same photo all the way out. The data file said 200. If it was a real 200, I would expect the lens to have brought me approximately 1/3 closer to the subject than it did at 150. Results: NO WAY THIS IS A 200!
Time after time the difference between the 150 and all the way out, was at most 10 or 15% more. Not very dramatic at all. Could I measure this? Perhaps, but I simply used my eye.
If this has been noticed before, does anyone know if Sigma has commented on this? Would you imagine this is a poorly calibrated lens, which should be returned or exchanged, or is it the entire lens line? If it is the line, I'm a bit more than angry. It sounds like a fraud or other consumer scam.