Originally posted by BigMackCam one lens - a zoom - showed that it is very slightly softer on the right side than the left (at the outer 10% of the image);
Classic case of de-centering, this isn't uncommon, zoom lenses are optically complex the more elements in the lens design the greater the chance is for something to go pear shaped.
Originally posted by BigMackCam another - also a zoom - showed that, wide open at the longer end, the slight halo around white lettering against a black background is always slightly up and to the right side of that lettering rather than a consistent "glow" all around. This is looking at 1:1, even 2:1, and even then, the issues were far from bad - but they *were* noticeable.
Sometimes when people see a problem their anxieties tend to focus, and magnify a problem - rather than the real consequences of it, which can be mild to non-existent. The solution to this issue is simple - stop the lens down. Which is what you should be doing in any case, as a vast majority of lenses perform best at 2 stops down from their widest apertures.
Originally posted by Sandy Hancock If you want to make a living from architecture, product, or astrophotography for example I imagine even slight optical problems will be important.
^ this. I own a specialized optics testing bench which is used to project various laser etched test patterns through a lens, each pattern is designed to show up any optical flaws. Using this bench removes the camera from the list of variables that affect image quality. Every lens I have ever bought has been mounted on it and scrutinized*. I test new and old lenses for colleagues because many of them simply don't have the time or equipment for the kind of precise optical testing I can do. I have saved myself and my colleagues both time and money from substandard copies of lenses - and from agonizing over it. If I don't the lens a thumbs up, it is time to get another copy.
*which isn't easy as the bench, which is made by Zeiss is actually designed to test medium format, 4X5 and 8X10 lenses. I have to use modified lens boards to mount 35mm lenses on it. Lenses with electromagnetic diaphragms and by-wire focusing systems in Nikon F/Canon EF mounts have a battery powered mounting board that cost nearly a thousand dollars that allows for focusing and aperture control.