I recently read in the DCResource forums about how large power zoom lenses like the Sigma 18-200 was coming up short on its stated focal length. Then I check out my Sigma 24-135mm and noticed it was coming up short too! Since I had an array of options at the 135mm focal length, I decided to check it out. Am I missing something and this is just a mere relation to the lens diameter or does my Sigma really come up short?
All tests done with a tripoded GX-1L. ISO 200, F8, 2.5sec, -0.3EV, Cloudy WB preset, Self timer 2 sec w/ mirror lock up. No PP, just resize (Web Large - 640x480)
SIGMA 24-135mm f2.8-4.5 Asph. IF
RICOH XR Rikenon 135mm f2.8
SMC PENTAX-M 135mm f3.5
MC Pro Rokinon Auto Zoom 80-200mm f4.5
And here are the lenses themselves.
Going Left to Right: Rokinon 80-200, Sigma 24-135, Ricoh 135, Pentax 135
Shoot I just noticed I forget to zoom the Sigma out to 135mm for size comparison. Oh well.
So what are your thoughts and ideas on this issue?