tdekany said "It is more beneficial to focus on taking “artistically and creatively” better photos. If you don’t see a difference with filters, good for you."

Yeah , sorry about the lack of artistic merit, I was just looking for a convenient scene with enough detail to be a valid test of filter caused image degradation. A good artist knows his tools and how to use them. Thankfully , If there was any degradation, it was so minimal that it made no practical difference. The lens was an Amazon.com used purchase from Japan and arrived with the filter already on the lens. Is there a filter maker in Germany named B&W? The markings on the filter circumference are "xs.pro digital, Made in Germany, B&W."
It seems strange that a lens sold in Japan would come with a German filter. I think I'll leave the filter attached for now because I'm going to a slot canyon in Arizona soon and the guides there throw sand and dust up in the air to highlight the sunbeams that are penetrating into the canyon. I'd much rather risk the filter be damaged by sand and dust than the lens.

abject failure getting the second photo to attach, giving up. The upshot is that I could see no differences on my monitor screen. That makes tdkany's comment all the more relevant.

OK got one photo to attach, working the next one now.

Yeah I know, I'm still a newby here and trying to figure out how to attach the photos

In a previous post the poster had a bad UV filter that seriously degraded his image quality. My response implied that perhaps the problem was an autofocus error such as I had experienced. Perhaps caused by trying to focus through the filter. That got me to thinking, so I took the suspect lens out on the porch and shot one photo with, and another without the filter attached, Here's the photos , can you tell which one had the filter?

My Sony A77 automatically registers the gps position in it's exif data. No seperate GPS or smartphone required

I was going to add that zooms that go into the telephoto range are usually noticeably softest at their maximum focal length setting. I used to have a 70-300 f/5.6-f/8.
I found that by shooting at 200 mm and cropping the resulting photo to 300mm magnification, I got noticeably sharper photos than if I had taken the photo zoomed all the way to 300mm. Perhaps SOME of the unsharpness you experienced was due to shooting at full zoom (70mm on your 28-70 zoom)

It's interesting information in the uV filter discussion. My used 17-70 came with a UV filter attached. I didn't even know there was a filter there until a week or so ago. ( I just thought that the front lens element was flat. ) I'll have to run some tests with filter vs filterless. I sent that lens to the importer's service department because of inconsistent focusing error. Sometimes front focus, sometimes back focus. When I got the lens back it still had the same malady just much less intensity of focusing inaccuracy. I wonder if I really only needed to remove the filter to achieve the same focus accuracy as with my other lenses.