At the time it came out, and even today I consider it to be an incredibly good camera. It was the first camera I owned where I thought if they never get better than this'll it's OK. I had one converted to infrared and still use it today. The on-off switches get a little stiff, that's about it.

A polarizing filter can really help at times. Even leaves often reflect the sky and can kill color. Polarizers also help pop out clouds and darken the skies. They also cost you over two stops of light most of the time. They only really work perpendicular to the sun as far as sky is concerned. In film days I left one on my camera most of the time. With Photoshop it's not as necessary, but can still help at times. With low ISO settings a tripod can become almost necessary. Any polarizer works, it's just that the circular models read the exposure better on most late model cameras. Few use them today so picking up a used one cheap and trying it out should cost next to nothing. More saturated colors because of the elimination of glare is the main advantage, but bringing out clouds against the sky is probably the most common use. Slight color variation between brands is common.

The way to avoid wide angle perspective distortion is to keep the camera level. Any lens, but especially noticeable the wider the lens, will do what you saw when the camera is not level. Tilt-shift lenses are made to deal with the issue.

If you have an appreciation for landscapes Joshua Tree Nat Park is about 1 1/2 hrs drive and one of my favorite places to photograph. The are digital B&W infrared, but color works as well.

I've had filters stuck so bad that I had to use a file or hacksaw on the metal filter to remove them. Usually something I bought used that had been cross threaded. Ruins the filter, saves the lens.

Changing the white balance from auto to shade or overcast should do the trick. On auto it tries to neutralize the color.

Basically eliminates shadows since light is coming from circle. Used a lot for macro, but can produce unique results in portraiture. Distance from subject male a huge difference. Usually fits around the lens so the lens is centered in the ring.

I've been shooting IR since film days and the uncertainty is part of the charm for me. I've played around a lot with settings and personally prefer ISO 400, F8, JPEG VS RAW, and high color saturation. I usually shoot in "A" mode with +1 exposure. Some I'll edit to B&W, others I leave as color. I tried RAW, but prefer JPEGs. I shoot 100% RAW with regular cameras. My IR cameras are Nikon D7000 and D40.

Brands matter little. Models within the brands matter a lot. Mirrorless vs DSLR is a personal choice and somewhat dependent on subject matter.

I don't just blast away. I compose and adjust settings knowing with a good deal of certainty what I want, and how to get it. I shot film for many, many years and the cost of pushing the shutter release was between $.50 for 35 mm to $15 on 8X10. I still tend to shoot very conservatively. When I travel I edit and upload every night before going to bed. 25-50% of daily shots are used, and I'm particular. I usually choose between slight compositional differences as I expect to have well over 95% keepers. I probably don't actually discard one percent. But of course subject matter makes a huge difference. Shooting birds in the air nets a much lower percentage of keepers. Slight exposure bracketing on sunset and sunrise pictures gives me choices to best edit from. When shooting a wedding or party I expect to only toss 3-5 shots out of several hundred. I heard a woman say she got about 75% of her wedding shots that were usable. What were the 25% that were missed?

You were at 1/40 sec and F4. Too slow SS to stop movement, and too shallow dept of field to get both subjects is focus at the same time. ISO 1600 rather than ISO 250, and maybe 5.6 would have done the job. Also, depending on where the focus spot was, the center of the image has very little contrast or detail to focus on.

The camera looks for contrast to focus. If it's pointed a something lacking detail, like a clear sky or clothing lacking textural detail it won't fire if it's set up in the menus to acquire focus before firing. Overriding the focus lock will let it fire regardless of acquired focus, usually not a good idea. Look for something at the same distance that has detail, push part way to lock focus, keep the button partially pressed and recompose and finish the shot. This won't work if you are set to autofocus continuously. There is a button on the AF-M lever that blows you to change the setting in the top menu. Try AF-S rather than AF-C.

I'd suggest getting a good exposure and changing to "M" exposure dialing in the SS, Aperture and ISO manually as was on the good shot. Your meter is the culprit and the exact position of white shirt or black pants gave a different reading. If the light doesn't change, the settings won't need to either. Matrix type metering would usually average between the white and dark, but spot metering would definitely give different readings.

Not sure I understand. Do you convert the already edited and deeply saturated shot, or start from the original when converting to B&W. I recommend starting from scratch. In Photoshop I've found the B&W adjustment very important allowing the adjustment of colors separately into B&W, allowing more control and separation of different colors that are similar same tones in monochrome.

I've had similar problems on both the Tamron and Sigma 24-70-2.8 lenses. I bought new rubber for the Tamron for around $10 on Ebay and used a rubber from a broken Nikon 18-70 on the Sigma.