I did a bunch of tests with filters on and off, comparing at 100% magnification. And this with moderately priced filters. The results were:

1. No perceptible loss of sharpness in any case.

2. Generally no perceptible loss of contrast, except some slight haloing around extremely bright sources of light shot head on.

3. In very rare cases of extremely bright point sources of light, one weak extra flare.

My personal practice is to keep UV or MC clear filters on every lens, occasionally removing them if I have the sun in the frame. I collect vintage lenses and almost every one exhibits some cleaning marks. It is easiest to replace a filter than a front element.

This is a summary of the "best practices" used by top working pros who seek optimal technical quality.

> There is no optical advantage below about a mile above sea level, unless you use film. Digital sensors don't pick up a lot of UV. There isn't enough UV at low altitudes to affect digital exposures.

> A UV filter is habitually sold by camera stores, because the store probably makes more money on filters than they do on camera or lens sales. These days, they should be selling a *clear glass* "filter" (lens protector) for the reasons they tell you that you should use a UV filter...

> Although a clear glass filter is better for lens protection than a UV filter (on DIGITAL camera lenses), in a pinch, a UV filter can protect your lens from flying debris, splashed liquids, sand, many drops, and other mishaps. It removes about 1/6 of an f/stop of light. Clear glass removes about half that.

> For night time street photography or astrophotography, or any time you have a lot of point source lights in a scene, REMOVE all filters if the situation makes it safe to do so. Filters can cause light to bounce off the front surface of a lens, reflect off the back side of the filter, and then be picked up by the lens in a different place. This can cause a weird "double image" flare, halos, or ghosting.

> Know that any filter can add significant flare to scenes with specular reflections (mirror-like reflections of light sources off of metal or glass or liquids) or light sources visible in a scene.

> Use filters when you need them for a specific purpose. Avoid them when you know it is safe to do so.

> ALWAYS use a lens shade.

> Use a clear glass filter, or a circular polarizer, or a neutral density filter, when the situation calls for it. At 6000' or higher, use a UV filter.

> Use special effects filters only if you can't get the effect in post-processing. Post-processing options are almost infinite these days. Recording and developing raw files maximizes your options for different end uses.

In my film days, I carried up to 40 filters in my bag, for B&W effects, special effects, and color correcting various light sources for both Daylight and Tungsten balanced Ektachrome films.

> In the digital world, white balance and hue controls (in the camera and in post-processing software) get rid of the need for color correction filters.

> B&W images may be created from raw files in many different ways, with near-infinite variations, so the old red, yellow, orange, and green filters used at the camera are unnecessary — in fact, undesirable — for their former effects. Just record raw files and convert them EXACTLY the way you want them, in Lightroom and Photoshop or your choice of good post-processing software.

In short, UV filters play a very minor role in the digital world, unless you're in the mountains. CLEAR GLASS "filters" or lens protectors should be used instead, and only when needed for protection. Lens hoods should ALWAYS be used, unless you're using an extreme wide angle lens where vignetting might be an undesirable effect. The most common "effects" you can't get in post-processing are circular polarization, which darkens blue skies at right angles to the sun and removes glare from foliage and water, and neutral density, which allows wider apertures, or slower shutter speeds, or lower ISO, or some combination of those.

1. Their has not been a UV filter manufactured yet that IMPROVES image quality.
2. 99.9% of the lenses made do not come with UV filters, I wonder why lens manufactures don't include one, maybe they know something you should.
3. A lens hood provides the best protection for a lens and front element.
4. A UV filter does not prevent dust from reaching the front element of your lens, if you leave that front filter on and just clean the filter, dust WILL get on the front element and WILL degrade your images, and a residue will also form on the front element. You must take the UV filter off from time to time to clean your front element, so what is the point of putting it on.
5. In the winter when you go from a warm house to the cold outdoors, you will have to clean that filter cause condensation will form on it, but also, a little will form under the filter on your front element, how ever slight it will still degrade your images.