why align your enlarger?
Since the '40s, improvements in enlargers have lagged behind improvements in cameras. Most photographers make small prints, so they base their needs on observations from those prints. But because small prints do not tell the complete story, the trend that started in the '40s continues today.
After zig-align began in the spring of 1987, every inquiry it has received about enlarger alignment has been from someone noticing that one or more corners of a print are not as sharp as the other corners. Everyone has assumed that better alignment would solve the corner problem, but everyone also has assumed that improving uniformity of sharpness is all that alignment would do. After using zig-align, not only do they get uniformity, they discover that alignment can have other benefits.
Optimizing the performance of your enlarging lens is the main reason to align your enlarger with maximum precision. Making your enlarger planes parallel to the paper can take you way beyond the problem of soft corners, enabling you also to preserve the performance of your taking lens. Observations based on prints just do not reveal the entire situation (this subject is discussed in the Alignment Checking Methods section of The Basics).
Digital photographers can make accurate visual inspections of final image quality because they can conveniently view very high magnifications on screen. They do not look at small prints. Although digital photographers have no need for enlarger alignment, many are discovering that zig-align helps them make better copies. For traditional photographers using enlargers, as well as for some digital photographers, zig-align's type of optical alignment optimizes performance of your enlarging lens. It's user-friendly, though significantly more hi-tech than any of the old ways
Any optical alignment is more sensitive than any mechanical alignment. But lens performance is maximized when using optical alignment that shows a symmetrical pattern of repeated images made by two facing mirrors, only when those mirrors are parallel. This kind of alignment can be 32 times more precise (based on a two-foot distance between planes) than any one-mirror system, such as a laser.
Homemade devices that almost certainly do not take advantage of the precision available in CNC milling, mechanical measurements (such as rulers, grids, etc.), and one-mirror systems simply do not have enough sensitivity to even approach maximizing the capability of a lens.
Most enlargers have relatively good alignment between the two enlarger stages (lens and negative), but enlargers usually lean forward, so they tend to have poor alignment between the enlarger stages and the paper. In addition, positions of the enlarger's light head on the upright, bellows draw, variations in temperature/humidity, vibration, and normal wear and tear can cause alignment to change. Also, manufacturer's failure to make enlargers easy to adjust leads to infrequent checking, a really poor practice.
Photographers might want enlargers that are as well aligned as cameras, but general expectations of alignment and difficulty (before zig-align) to adequately judge enlarger alignment allows the technological gap between cameras and enlargers to persist.