[rbefly]

Recently I took a "nature" walk, hoping to find a suitable scene to try my new neutral density filter #16. Some moving water, perhaps?
Along the Cherry Creek bike path, I found a rocky downslope that looked promising. The sun was a problem, I was shooting nearly straight into it, but because of the terrain and rocks, it was the only suitable spot for my tripod.
I set up and took an establishing shot (photo # 1), K10D, Pentax "A" 28mm, f/8.0, 1/60s, no hood, no CPL, no ND. Pretty bad, huh? Glare, washed out, no contrast. Yuk!
Photo # 2. Added a generic W/A lens hood, same f/8.0, same 1/60s shutter speed. Slightly better glare control and contrast, still not good.
Photo # 3. Added Marumi 49mm CPL set at max contrast, still using hood. The CPL lowered the shutter speed to 1/20s with the same f/8.0 aperture, so, about 1-1/3 stops compensation. Again, better contrast, sky and clouds improved, water flow slowed down but not great, overall.
Photo # 4. Now I added a ND #16 to the CPL and hood. Shutter speed 0.7s, f/11.0, we're getting somewhere! Much better contrast, colors and the water flow is much smoother.
Photo # 5. Increased f/stop to f/19.0, shutter speed 4.0 seconds, still using hood and CPL. Best contrast, glare is gone, water flow smoothed out pretty well.
In the interest of full disclosure, the ONLY PP used was a slight lightening/darkening of # 4 and # 5, to even out the brightness, there was a small difference in the overall value compared to # 1, 2, 3. That's it, no contrast changes, no color added, no boost, all photos are RAW, ISO 100, full frame. I used aperture priority, tripod, cable release. The EXIF will show a lens size variance, that's user error, I forgot to re-set it from the previous lens. No shake reduction anyway, it was turned off.
Eventually I tried f/22.0 and got a shutter speed of 6.0 seconds, but had moved the camera to a different scene; The water flow is even smoother. But, I wanted to show the same scenes here, for comparison.
Hope it's useful!
Ron

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[vladimiroltean]

So you're actually saying that filters can reduce glare instead of introducing it?

[Na Horuk]

Well, a polarizer certainly affects the light coming into the lens, so it can probably be used to block out some of the glare. If its a high quality filter it won't be much worse than the lens itself, and using a hood over it will solve that problem. Polarizers lower the contrast of the scene, which allows the camera to capture all of it (this in turn looks like "high contrast" on a photo)

[rbefly]

So you're actually saying that filters can reduce glare instead of introducing it?

Not any filter, no.
But polarizers do, and quite effectively so. Glare, that hazy "fog" or overall soft, lack of contrast effect is the result of light bouncing in all directions, off any reflective surface or even the ground, snow, etc. Random light, as opposed to directional light.
Polarizers "straighten" out the light, allowing only directional light to hit the sensor or film. It can easily be seen with the human eye, by simply holding a CPL in front of your eye and turning the front element. When you reach maximum effect, clouds will pop out of a blue sky, glass reflections will disappear, allowing the viewer to see "through" shaded or reflective glass and you can "see" underwater, even though (to the naked eye or unaided camera sensor) the water is too reflective to see through.
Most other filters can introduce glare and especially flare, because they add an extra element (glass) that is not as well-coated, is lower quality material and sits too far ahead of the main optic, allowing light to bounce around in a way that is not accounted for in the lens design.
Most filters degrade the image quality to some degree. This may be compensated for, by the change the filter itself makes, such as color enhancement, color temperature correction, etc.
Polarizers enhance the image without an optical disadvantage (at least, none that I've ever seen, perhaps deliberately trying for reflections would be an example) but they DO have a mechanical disadvantage; About 1-1/3 to 1-1/2 stops of light reduction or compensation.
JMO, YMMV,
Ron

[Not a Number]

Maybe exposing "to the right" would achieve similar results?

Expose Right

[Na Horuk]

While processing can achieve all sorts of things, there are some things it cannot. It cant add missing highlights, it cant do the effect of CPL filters, it cant change the DoF.. so using a filter can be very important for some scenes

[vladimiroltean]

Not any filter, no.
But polarizers do, and quite effectively so. Glare, that hazy "fog" or overall soft, lack of contrast effect is the result of light bouncing in all directions, off any reflective surface or even the ground, snow, etc. Random light, as opposed to directional light.
Polarizers "straighten" out the light, allowing only directional light to hit the sensor or film. It can easily be seen with the human eye, by simply holding a CPL in front of your eye and turning the front element. When you reach maximum effect, clouds will pop out of a blue sky, glass reflections will disappear, allowing the viewer to see "through" shaded or reflective glass and you can "see" underwater, even though (to the naked eye or unaided camera sensor) the water is too reflective to see through.
Most other filters can introduce glare and especially flare, because they add an extra element (glass) that is not as well-coated, is lower quality material and sits too far ahead of the main optic, allowing light to bounce around in a way that is not accounted for in the lens design.
Most filters degrade the image quality to some degree. This may be compensated for, by the change the filter itself makes, such as color enhancement, color temperature correction, etc.
Polarizers enhance the image without an optical disadvantage (at least, none that I've ever seen, perhaps deliberately trying for reflections would be an example) but they DO have a mechanical disadvantage; About 1-1/3 to 1-1/2 stops of light reduction or compensation.
JMO, YMMV,
Ron

I think you have that quite wrong. Wave polarization has nothing to do with direction of propagation, but with the orientation of the electric and magnetic vectors in relation to this direction. And the light loss you are talking about is not at all mechanical