Hi DanLoc78
I have owned the Tamron version of the 18-250mm for about a year now and have been delighted with it's sharpness and indispensable flexibility of focal length. Admittedly it does suffer from slight 'lens-creep' if the lens is pointed downwards under it's own weight, but it simply becomes a matter of habit to engage the little locking-switch to prevent this happening before starting to walk around. There is a tiny amount of vignetting at the wide (18mm) end, which is probably due to the protective UV filter I attached to the lens in order to safeguard the vulnerable front lens element. However, vignetting can easily be removed nowadays with most half-decent software editing packages. To view some images taken with this lens, try this link:
https://www.pentaxforums.com/forums/171724-post3.html
and then click on the the three links at the bottom of the post.
In addition, I have to agree with Derridale when he said:
Quote: Heather - why use a polarizer AND a UV filter at the same time?
The stacked combination of two filters (one in front of the other) would probably cause SERIOUS vignetting on the vast majority of wide-angle lenses at their widest ranges. Personally, I would have used either one filter OR the other, NOT both combined, but that's just my own thoughts on the matter.
Best regards
Richard