E.L.. Shapiro Loc: Ottawa, Ontario Canada

High-quality optical glass filters should not cases appreciable "blur". "Optically" speaking, image degradation due to filter usage is caused by defects in the glass, poorly crafted filters, damaged, dirty or delaminated filters, or uncoated filters causing excessive flare.

Anything, even the finest filters, that you place in the light path, technically, can cause some aberration or defect, however, it may be so infinitesimal that it can only be detected by special instrumentation.

If you purchase B+W, Zeiss, or Schneider filters or some of the other time-honored brands, you will not experience "blurr" issues.

Actual blur is usually caused by subject or camer movement at slower shutter speeds, a defective focusing system, or improper focusing technique.

This is an old tired debate. If you feel that a filter will degrade your images- don't use any. If your work is going to be subject to a great deal of enlargement in its eventual display, maybe that might be a good strategy. If you are workig in hazardous conditions such as salt water spray, industrial pollution, airborne particles, steamy kithes with splatter, rough terrane. etc, you may want to consider protecting your lens.

The examples posted by the OP show an excessive IQ degradation- that would have to be one messed-up filter! Dollars to donuts- the causes are camera movement, mirror slap, or impractical shutter speed with
inadequate support.

Buy your filter from reliable sources and run your tests under more controlled conditions with a solid tripod, careful focus technique, and a clean spanking new good filter.

jerryc41 Loc: Catskill Mts of NY

That's pretty bad. Totally unacceptable.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

B&W makes a great quality filter. That said a UV filter usually is a waste of time. I have not used a UV filter since going Pro many many many many years ago.
Personally the only time a UV filter should be used is around salt water spray, close to house fires, and dust and tornado storms.

anotherview Loc: California

Ditto.

NikonZSeriesMike Loc: Naples, FL

I use B+W filters exclusively. I’ve always had good experience with them.

mwsilvers Loc: Central New Jersey

How Much Blur from a UV Filter is Acceptable ??

The answer is none. If any filter, not intended to add blur, adds obvious blur to any image the filter should be relegated to the trash bin.

gvarner Loc: Central Oregon Coast

I’ve seen many comments here that a UV filter is not needed for digital photography. I use one just to protect the lens. I’ve seen no distortion.

larryepage Loc: North Texas area

I use filters for protection on every lens. I prefer to clean the filters rather than the expensive coated front elements. But I use clear filters, not UV or "Skylight" or "Haze" filters, except for a couple of leftovers that haven't been replaced yet. It's not a super-critical difference. Not using cheap filters is important.

And yes, every lens also has a properly installed hood also. But I've demonstrated to myself that they don't provide the level of protection that lore ascribes to them in case of a fall or drop.

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

I use clear, not UV, but the same reason.

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

Agree

Nicholas J DeSciose

Real photographers don’t use UV filters

therwol Loc: USA

They might if they're still shooting film, especially color transparencies. They do make some difference in outcome.

photoman43

I agree with CHG CANON. I have been buying B+W filters from B&H for over 20-25 years.

MJPerini

Never base buying decisions on a single test, and make sure your test is a rigorous one.
Use a known focusing target if possible. Tripod and bean bag or dead arm weight on the camera, self timer or electronic cable release. Do the test multiple times until you get repeatable results.
Vivitar products are built for low cost.
You can pretty much tell premium filters by Price. B&W & Heliopan have the best reputation, but other companies make some fine products as well.
A good filter is basically a single element lens built of optical glass, and ground to be plane parallel on two surfaces and multi-coated on two surfaces, with a threaded mount that assures that it mounts perpendicular to the lens axis.

Burkley Loc: Park City

B&W clear filter from B&H or Adorama. Never a quality problem. I generally use them to protect the edges of the lens casing when hiking, not so much the actual glass.