G'day EdZz

One of the many laws of our economic world says something like "you get what you pay for"
Another says that "eventually you run out of money chasing something that is only marginally better than something-else at a lesser price"

There is no doubt that the OEM makers DO make a special line of pro lenses, sold under their own brand name and often hand-assembled with great care to ensure the highest standards ... and you, the photographer pay for that privilege

However, for most of us who have a budget to adhere to, we do the dance between the 'regular' (non-pro) lenses from the OEM maker vs the 'regular' lenses from the 3rd-party lens makers

I have used many 3rd-party lenses over the past 40yrs of SLR photography ... and I have found Tamron best suit my needs. I used to test my lenses via a shoot on ISO-40 B&W film, then blowing up the neg to a 40-inch wide image and printing a series of 4x6" prints across the centre as well as the four corners. I have been surprised at the sharpness of the Tamron "SP" lenses, as well as (occasionally) others who would be snubbed by many big-nob photographers

Please don't mis-interpret the above as suggesting "only Tamron" - other makers DO make very good lenses ... you need to examine & test each possible lens in the shop before buying the one that suits you best. Most shops will let you stand at/near the door and shoot a series of test pix for later evaluation

Hope this helps a bit
Regards, Phil