Originally posted by Merv-O Really appreciate the time that you're taking in discussing this issue....
You're very welcome
Originally posted by Merv-O I like shooting in manual focus regardless, but the improved AF on the K-1 ii should be better than what I've been seeing. The TAMRON is a comparably priced to some PENTAX glass, though I liked the idea of f/2.8 in a mini telephoto. I'll keep the FF issue in mind as well. I wish I had joined this Forum before I bought some of my other kit lenses (i.e, PENTAX 50mm 1.4, 35mm f/2 primes) . Better late than never I guess.
For a 28-75mm f/2.8 constant aperture lens, the Tamron is actually pretty cheap - especially when you consider street prices and look for deals. It's right at the low end of pricing for that class of lens. In fact, I don't know of another full-frame constant f/2.8 zoom covering those focal lengths that is anywhere near the same price. You can get better image quality from other the lenses for the same or even less money, but then you don't get the focal length range and constant f/2.8 aperture.
Contrary to one of the earlier posts in this thread, the Tamron 28-75 f/2.8 focuses perfectly well using Live View, and that doesn't require AF fine adjustment as it uses contrast detect for auto-focus. So, to see what your lens is capable of, take some shots in Live View instead of focusing through the viewfinder. Make sure to keep your shutter speed at
1 / focal length or faster, and don't go below 1/60s. Do this in good lighting conditions. You should find that you get good results, especially when stopped down to f/4 or smaller (but even f/2.8 should be decent). Then, work on AF fine adjustment so you get comparable results when focusing through the viewfinder.
If you can't get good results using Live View, there's something wrong - either with your chosen exposure settings, or the lens. It will most likely be the former - but there's a small chance the lens could be at fault. Feel free to post any test pics if you'd like any more input