Bipod wrote:
...
Anything you add to the front of a lens reduces flare. The worst surface that
the sun can strike is the objective (front) element of the lens, because it is
convex and thick.
So, in the absence of a good lens hood, screwing a piece of multi-coated plain
glass to the front of a lens often reduces flares and improves contrast.
....
Sorry, but this is utter bunk. Exactly the opposite is true. Filters INCREASE flare when the sun strikes them!
If you don't believe me, go shoot a sunset directly.... Once with a filter, once without it. I guarantee you that the shot with the filter will have added veiling flare and ghost flare artifacts. Higher quality, multi-coated filters will add less flare than cheap, uncoated filters... But ANY filter will increase it to some extent when the sun strikes the filter directly, such as when shooting a sunrise or a sunset.
A polarizing filter is one of the worst for this, because it has multiple layers of glass. (Besides, a polarizer has no polarizing effect when it's pointed directly at a light source.)
Below image was shot directly into the sun with a high quality, multi-coated circular polarizer on a lens that's pretty darned flare resistant:
There is overall veiling flare that's washed out colors and reduced the contrast in the above image. In addition, there are a number of ghost artifacts plus chromatic aberration was amplified.
Here are some enlarged details from that image, with many of those "issues" pointed out (most of the ghost flare artifacts are quite small and may be difficult to see at Internet resolutions):
Actually, the above image came out better than I expected. With some work in Photoshop, I was able to fix many of the issues. The chromatic aberration was the most difficult, because it's blue/yellow CA in the center of the image and green/magenta toward the edges! Below is the corrected image with the ghost artifacts retouched out, contrast and saturation boosted considerably, and more:
But most or all that additional work could have been avoided simply by not using a filter on the lens, as was done for the shot below which required almost no retouching or post-processing at alll:
Finally, a good, well-fitted lens hood should virtually always be used. It won't help when directly shooting sunsets and sunrises, where the sun is actually in the image or very near to it. But it will help in most other situations, by keeping oblique light off the lens (AND any filter you might be using). In addition, while shooting with the lens, a hood provides better physical "protection" against bumps than a thin piece of glass ever could. (A lens CAP provides the best protection when storing the lens.)
When I got my Canon EF-S 10-22mm ultrawide I was surprised by how large and cumbersome it's matched lens hood was. It's like a small Frisbee! I knew the lens was highly flare resistant, so thought maybe I could just leave that hood at home (I always carry and virtually always use hoods on all my other lenses). So I decided to test it with and without the hood. Here are the results... Left image without the hood, right image made with it installed (the clouds moved a bit while I was installing the hood).
Needless to say, I always use the matched hood on that lens, too... even if it's a bit of a pain to stow in my camera bag.