The lens does not matter--for objects that big, you do not need macro. It may help to use a longer zoom setting and back up, though technically that does not matter, either. It has to be a physical problem in the plane of subject and plane of image.

Bob,
If the top line is straight horizontal, and the bottom line is seriously off-horizontal, this:
could not be camera merely swung left or right but perfectly upright
could not be picture merely swung left or right but perfectly upright
could not be camera merely tilted to or fro at top or bottom (but not swung left or right)
could not be picture merely tilted to or fro at top or bottom (as on an easel) (but not swung left or right)

Either the camera or the picture would have to be diagonally slanted and tilted in relation to the other, yes? Isn't the only easy way to align the edge of the subject with the edge of the image--visually--so that the top and bottom are parallel in the image, then shoot what you see?

Something was also said about reflections--light should come from the sides equally, or even skylight. or Sun from either side (the Sun is equally distant from both sides). If the texture of the object is wanted, specular light will highlight it (small light source), or if the brush strokes (for instance) are not wanted in detail, diffuse light will subdue it.

Copy stands are not free, but could be considered. One could also contrive the equivalent (Google).

What you describe is not caused by the lens (as proven by the fact that both lenses do it)--and certainly a Nikon lens won't make a rectangle look anything but square at the four corners. If the corners are not 90 degrees, something is not lined up--either the camera (does yours have a bubble level? You can buy a small cheap carpenter's level) is tilted, or the art is tilted, either vertically or horizontally--possibly both (diagonally). You probably need a tripod for this sort of thing.
The infallible plan is to look at the image before shooting--what you see is what you will get. Tilting every which way will cause lines to converge in different ways--but you can see this before you shoot. Align top, bottom, and sides of object with the sides of the camera image. Some cameras have a grid on the visual screen for this--you can turn it on or off. If the plane of the sensor is exactly parallel to the plane of the subject, it will look the way you want--period.

Note--"distortion" in a lens is a tech term. Google it for correct usage. Popular usage is different--and not very precise.

Shooting farther back (with normal or long lens) may lessen the effect of angle-error, unless the picture is very much enlarged. Wide angle lenses are often used for deliberately distorting the perspective so that parallel lines seem to converge--vertical lines or horizontal lines.

Personal choice, but I think what is best should depend on the shot. Bold graphic outlines can be effective on matte, also pics where finest detail is not critical (or undesirable). Matte can suppress flaws to some extent, and could reduce reflections when framed. But traditionally, glossy prints show off quality best where sharp detail is wanted and reflections are not an issue.

I like your thoughtful reply--about composition depending on the subject itself and on one's purpose. Certainly commercial purpose is a factor, but not the only one (artistic purpose). However, I would make a simpler point--that the cropping is part of deciding what you are taking a picture of (your subject). Often the weakest element of snapshots is that you don't really see what it is supposed to be a picture of. To me, too much cropping of a subject removes the element of composition entirely (or nearly so), while too little loses the subject in extraneous distractions. This is a very artistic judgment. The Ansel Adams "portrait" of a woman standing in her garden--90% of it is garden--puzzled me at first, but on reflection it is clearly a picture of the woman with what she loves, a picture of romance. Andy Warhol shocked everybody not by painting a tomato soup can, but by painting it just by itself--no composition (and that was an element of his style). Advertising may want to impress upon our minds and memories the bare and simple image of a product--or they may want to show the product in use, with people. They are not pictures of the same thing. Is it an exaggeration to say that "What is this a picture of?" is the most elemental question in cropping? The answer to that question has both subjective and objective elements. It is too subjective to say a picture of a soup can is a picture of your mother, because this departs too far from the objective world. But a picture of mother serving soup for lunch can be a picture of love, yes?
One time I asked some photographers how they would photograph love, and all I got was wedding picture ideas--beaches, the sea, all sorts of backgrounds for lovers. Nobody thought of grandma serving cookies to children. To photograph an abstraction, we need art and composition.

It is hard to get around the fact that both a wide and a tele lens are commonly needed for all-purpose shooting. This means either a heavier, bulky lens or two lenses. For cityscapes and street shooting, I tend to see in wide angle, but not always. In nature, it can go either way, but for wildlife it is almost always desirable to have the longest lens possible. Like Ansel Adams, most of us seldom go for "normal" lenses--long or short lenses add a selective aspect. But consider the traditional photojournalists of old, with their Graflex press cameras. They nearly always used a 135mm or 127mm lens for all newspaper work. This was a slightly wide normal lens, just wide enough to add a margin for error in composing and parallax. It would take some effort to learn to use a normal lens for all things, yes?

When the mountain will not come to Mohammad, Mohammad must go to the mountain. What I would like is a wide lens that is very light and compact (not necessarily superfast), and a long lens that is also light and compact (not necessarily superfast). There are designs for this, but they are neither zooms nor commercially popular (or available). A dialyte lens can be tiny, yet magnificently sharp (Kodak 203mm f7.7, Fujinon A 240mm f8, or the Schneider Angulon design instead). I would rather have several lenses the size of walnuts in my pockets rather that a few big, fast zooms. I would also rather have a Maserati than an old Taurus.

People have the same problem as the owls--paparazzi. Maybe if we had celebrity reserves they could get peace there. Not all celebrities asked for it--like children of famous people.

Before I replied, I knew people would talk about the background. The standard professional--or traditional--photographer is going to want the subject popping out, in several ways. One is to have a big difference in exposure. The background can be darker or lighter (high key). Second, the background can be out of focus (more so than here), either by being farther away, by using a bigger lens aperture, or shooting closer to the subject. The background might even move--using a moving train as background. Some people even stress about "bokeh," a made-up word about the way some lenses (due to the blades of their apertures) make the unfocused backgrounds dreamier, creamier, or anyway less screamier. Third, the background can be plainer, less busy with distracting things in it, or perhaps ideally, nothing recognizable or interesting. A plain or indifferently textured backdrop could be used such as a big card or the sky.

Part of the artistic decision is the genre--pictorial like Strand or, later, Adams, journalistic like Capa or Eisenstaedt, snap-shot movement like Eggleston, or other platforms and movements.

The rules are set for two main traditions--product photography and portraiture. The product jumps out, while the background is suppressed as above. However, both products and people can be photographed on entirely different principles. A product can be shown within its usual (or unusual) surroundings, which may be crystal clear. To some degree, traditional bonsai are surrounded by a mini-environment that seems natural to them, at least until they reach the pot, which is a sort of frame. A human model may be shown at the Eiffel Tower or the Grand canyon, again f-64 sharp and clear. Ansel Adams' textbook shows a portrait of a woman, full figure in wide angle lens, in her beautiful garden--which proved to many people that Adams was no portrait photographer. But the joke is on them.

The possibilities with bonsai are endless--and grand. A tiny pine with the trunk of a mighty pine as its background is just a thought. Or a forest of trunks behind it, in a variety of different lighting contexts and compositions. I am not sure what to do with a group-portrait for bonsai--they must not be lost in a maze (or perhaps they should be, in a large print?) If a Lexus can be photographed with a pretty model, so can a bonsai, yes? Or a lizard contemplating a bonsai might look like Godzilla has returned. One might set up a basic stage, such as a rustic bench or a modern one. Lighting, focus, and perspectives are always considered, but the general practice need not be worn like a crown of thorns. We first look at what everybody does (and ask, Why?) and then we look another way (and ask, Why not?) The common rules give us a diving board from which we may spring--not necessarily a sofa to lie down upon.

I use Canon, but the difference in 1.8 and 1.4 is in itself negligible--a fraction of an f-stop apart. A faster lens is generally more expensive--but also heavier. On the other hand, there are sometimes differences besides speed--a slower lens might be an economy lens. I doubt that is the the case here. f1.8 50mm is such a mainstay that it should be first quality. If speed is critical, consider f1.2. But remember that there will be virtually no depth of field at f1.2, and precious little more at 1.4. The gain in shutter speed is often lost in the loss of depth of field sharpness. Often the finest lenses in picture quality are not the fastest ones, just as the fastest films or highest digital ISO are not the finest. For the photojournalist style, remember that newspaper pictures do not have the finest sharpness, resolution, or tonal scale. They can still be great pictures, of course, of their genre. In the end it is a matter of mastering the available equipment in the circumstances, yes?

Wayne, I am near you in Fulton County, KY. I like the Canon Pro 100 too. I bought a very expensive Epson big enlarger, but never could get it to work--it would take hours and a lot of paper to get an (admittedly good) photo. I got the Canon, plugged it in, and I have arrived. I have the Epson V-750 Pro scanner, and it works.

My solution to the thousands of old negatives and slides was that when I moved to semi-retirement, I took all those boxes and put them in the dumpster. Almost everything I have is new now.

Thanks, Dick!

I am new here and I am surprised at how many people photograph birds. They are lovely, but very difficult because of the combination of being small, active, and far away. This calls for very long lenses, very fast lenses, and great patience (with a high ratio of misses). My yard in the country is full of them all year, but I gave up trying to get them to hold still for me.

The comments here suggest the need for a full-featured camera that has an even smaller sensor (cropping the subject even more). Fine 8x10 or 11x14 prints should be enough, no? Call it a telephoto camera. It is possible to make long lenses that are smaller and lighter--especially at f stops of f9 or higher. (Consider the old Kodak large format 203mm f7.7 lens that was ruthlessly sharp and covered 5x7 film, but was tiny. Or the Fuji 240mm f9 A that even covers 8x10 film. The Schneider Angulons were very small and light, merely f8.) Part of what makes the lenses bigger and heavier, apart from more speed, is the need for backfocus when placed in front of a reflex mirror--less a problem with long lenses. For long lenses, that ought to be large enough aperture for the depth of field a bird needs.

Also, is it possible to design a higher ISO without loss of image quality? Over time, it was possible to do that with film...

Maybe what we need are two cameras (wide and long), each modestly priced, rather than one all-purpose camera with many hard-to-design lenses. The wide angle could use Angulon design lenses, the long camera could use the dialyte design of the Kodak and Fuji lenses above. They need not be interchangeable, as the sensor-to-lens distances need not be the same.

Venturing further into Wonderland, why not make the sensor in your camera interchangeable? Go to the bigger sensor when needed, and otherwise use the smaller one for the obvious reasons (distance, more shots per card, etc.)

I like 'em all, but I still love the look of Tessar design lenses. My avatar here was taken with a 50-pound Linhof 8x10 camera with a Canon 650D on the back, on my front porch in existing daylight. It was a Carl Zeiss Tessar 360mm f4.5 lens, a huge chunk of glass.

Jerry, one important question--do you think everybody got this card, or was it just you?

The cat is obviously ready to party!