I've had the Kood 86mm UV Filter for a couple of months now with many photos taken to try & see what caused my poor photos.
I have only just got a new camera with the sigma 150-500mm lens, I needed a filter to protect it & I had read that the filter did not screw on all the way; I thought I can live with that.
I take wildlife photos, but with the filter on, I found the photos poor (soft), I thought it's because I needed more practice with my new kit.
With the filter on, I want around my garden taking photos of all the birds I could see, some birds were a few feet away, others 100 yards away. All the 100 photos came out poor, deleted the lot.
With the filter off the lens, went out into the garden again, took 200 photos, and deleted 50 of them because the bird moved while I was using a low shutter speed. 150 photos are great, good & sharp.
The reason the filter will not go on the lens properly, is because it has the wrong thread, if you do not tighten it enough, it falls off the next time you touch it. If you put the filter on tight, you can not get it off, so if you do need to replace the filter, you may damage the body of the lens trying to get the filter off.
This filter will not be going on my lens again.