Any ideas on what you are considering? Possibly Tamron?
any sharper and you'd have x-ray! Just kidding....I'm sure it could be sharper, but when's it sharp enough?
I'd offer up this thread as an example (from the Fred Miranda forum - not sure if you need membership to see it)
Finishing the Season with a Bang (30) - FM Forums
I'm not saying mine isn't
sharp enough. I've posted plenty of photos I'm proud of that are less sharp. But as I mentioned in the
Don't Hurt Yourself thread, I aspire to something better, and for wildlife there's a crispness (OK,
tack sharpness) that sets off the best from the rest, and I believe that to get it you need glass that performs. At this point I'm vacillating between a Sigma 120-300mm f/2.8 or biting the bullet and going just straight Nikon 300mm f/2.8, with TC's on tip of it (that Sigma is the
only 3rd party lens I'd consider for this purpose). There is definitely a level of sharpness to a fixed length prime lens that cannot be replicated with a zoom, and when I can peak at the EXIF data of those photos I admire most it seems that a long prime is being used. This is when a "hobby" becomes expensive. Thankfully I have some things from my 6-string hobby that have needed selling for a while and I can likely make this happen if I want.
Before that, however, I want to make sure I'm doing what I need to to maximize what I have. For example, this shot was handheld at 400mm. My opinion is that if I'd simply put this on a monopod that I'd likely have more crisp keepers, and might even raise the level of sharpness a touch. Develop that habit and if I'm still disappointed with the results then it's
justified upgrading. Until then I'm using equipment as
the excuse instead of
an excuse.
Thinking about it some more, I also need to go in and profile the D7100 with that lens (can't believe I haven't) along with a full set of profiles on the D600 and D610 which haven't been done yet.