If
you'll remember, I arrived at the RV Park early in the afternoon and decided
to investigate the area - about 10 miles back on the interstate and 30 miles
down a local road is a sandstone arch - a natural bridge called La Ventana.
It's visible from the road and you can get some good shots of it from the
road. The best time to visit is close to noon or early afternoon - the sun
has to be from above to illuminate the inside of the arch. If later or
earlier, the inside is in shadow as in this picture. 
This pic will give you a little better idea of why --
If you are inclined to hike to the arch, a moderate hike of only about 1/4 mile, you can make pictures like this!
To illuminate the back of the arch, the sun has to enter through the hole at the top behind the arch itself. So the best time to shoot is from about noon to 2 o'clock. I was there at about 4 o'clock so the sun was down slightly and the back of the arch was in shade.
The
obvious correction is not to use stacked filters on a wide angle lens. If
you think you need all the filters you have, then you can correct after the
fact by one of a couple ways - one, you can crop the corners out, two, you
can round the corners to make the final image look like a mounted 35mm
transparency which naturally has rounded corners, three, you can use your
Photoshop skills to edit the corners, or four, you can discard the image
altogether. Stacked filters can give you other problems too. Look again at
the lower right corner. I hid the sun behind the cliff, but there is a
little lens flare at about 2 o'clock to the sun. The multiple surfaces of
the filters can give you unwanted flare because of internal reflections.
Btw, I'm directly under the arch, which looks like it's ready to fall at any
time!
Here's
another problem you might encounter with filters - specifically a polarizer.
A polarizer organizes light waves and eliminates light scatter and in some cases, reflections. A polarizer is used most frequently to give you more contrast in the sky - which results in bluer skies with whiter clouds. The polarizer works best when shooting at a 90 degree angle to the sun's position. In the picture above, I'm shooting from the back of the arch at about a 45 degree angle to the sun. You see the result. The polarizer has darkened the sky closer to the 90 degree position (on the right) much more than it has to the 0 degree position (to the left). It's not an unpleasant result, you just have to be aware of it, that's all.
Here's a nice shot of the arch.
I also stopped at what's called Sandstone Bluffs Overlook. This is a tall bluff just at the edge of the McCarty's Lava Flow - the youngest El Malpais flow at only 2000 years old. (There are some thirty volcanoes and more than eighty vents and spatter cones in this area.) Here's a shot looking north at one section of the bluffs with the lava flow in the background. I used a polarizer but am just about at 90 degrees to the sun -- which is directly to the left -- so the sky color is reasonably uniform left to right.
Here's a shot of the main lava flow -- the dark part is exposed lava and the green is some of the vegetation that's managed to gain a foothold in the past 2000 years. The vegetation is growing in dirt and dust that's blown in from the adjacent desert.
Here's one I call
"Lone Sentinel."
