While reviewing my equipment choices for an upcoming visit to my daughter's family, I came across a Vivitar auto focus 100-300 zoom. I got it brand new and unopened from an Ebay seller, dirt cheap. I tried it a little and found its results to be unacceptedly soft. Put it away and forgot about it. I pulled up the photos I'd taken with it, and realized that they had all been shot in the camera's program mode, which seems to be heavily biased toward high speed shutter times, so the lens was wide open all the timel Decided to give it another try, this time forcing the camera to stop it down. The results surprised me to say the least. It still is not one of my preferred lenses, but will produce acceptable images if used properly.
168mm, f8, 1/1000, ISO800, handheld Minimal tweaking in Gimp
300mm, every thing else same as above.
The all plastic construction puts me off, and the auto-focus is slow, but seemingly precise. It is a relatively slow lens, and can only be used in good light.
Which did get mediocre review results. Telezooms are not easy to test, because a minimal shake will distort the image. I think you have made the lens stand out, crisp and clear images. May be the ISO has to be increased to get short shutter speed and stop down a bit, to get the most out of the lens.
A telephoto that has to be used at f8 would have no use in my golf bag, however good at that aperture. My go-to medium telephoto is the Canon 70-200 f4L and worth every penny of what it cost, around £500. I just wish I could justify spending £1600 on the 2.8 IS version.
One thing I have noticed with many zoom lenses is that the focal lengths are somewhat on the optimistic side on most of them. I did, a while ago, do some reasonably accurate comparisons which seemed to show an average of about 110% optimism.