| Latest Review Posted | SMC Pentax 200mm F2.5
I have never owned or handled this lens, so I won't put in any review numbers or comment on the quality of the images, but there is one thing that disturbs me very much about this lens.
It is the only lens in the Pentax lineup that is blantantly a "liar lens".
f-stop is defined as focal length / diameter entrance pupil
This being the case, the focal length is 200mm, the maximum diameter of the entrance pupil (or aperature) is 77mm (since that is the filter diameter) actual entrance pupil would be even smaller because of the edge of the rim.
200mm / 77mm = 2.597 as a theoretical maximum for f-stop of this lens.
Exaggerating on f-stop is common with many 3rd party lenses, but I have never found any other Pentax lens to be so blantant in this regard. Other lenses may not actually have the advertised f-stop, but at least it isn't theoretically impossible.
This lens should really have been advertised as a f2.8 |
