zig-align
and lasers
some opinion; some facts
There have been two laser alignment systems on the market (Parallel by Versalab and LaserAlign by Focal Point), both only for enlargers. These companies offer other types of products as well. There is one company offering two-mirror alignment systems, zig-align, which deals only in alignment and offers systems for enlargers, as well as for other equipment.
All laser systems use one mirror that reflects a laser beam once. This prevents the device from detecting small changes in parallelism, because there is only one visible path to the mirror from the laser and one from the mirror back to the laser beam hole. This technique shows you two units of error, which is the limit of amplification of error by any laser system. And unless the laser beam is normal (90º) to the bottom of the box containing the laser, results are inconsistent.
The first repeat of zig-align's two-mirror system uses just one mirror and shows the same amount of error as a laser system displays. But that is only the first repeat. Additional repeats continue to amplify the error.
When two mirrors that face each other are two feet apart (a common distance for enlarger use), the LED module displays six distinct repeats on each leg of its "X" pattern. Each repeat doubles the error shown by the previous repeat. Two to the sixth power (26) is the mathematical way of saying that the sixth repeat contains 64 times the original error. Thus, zig-align's last repeat is 32 (64 /2) times more sensitive than a laser system. This is why zig-align systems show even slight amounts of error. This is what makes the systems so user-friendly.
I know a photographer, a former owner of a machine shop, who compared Parallel to zig-align's LED module on his own enlarger. While raising and lowering the enlarger head, Parallel showed no deviations, but zig-align showed several major ones. When a production manager at a large photo lab compared LaserAlign and zig-align, he saw similar results.
The comparison of zig-align to lasers with respect to accuracy is dramatic, and also discouraging. Here I rely on data collected on my own enlarger using LaserAlign.
Both laser devices (LaserAlign and Parallel) are small, horizontal boxes with a hole for a laser beam positioned off center on the top of the box. In order for the system to be accurate and reliable, the laser beam must be perfectly normal to the registration surface, which is the bottom of the box.
I put a piece of glass on top of my easel and placed LaserAlign on the flat glass surface. When the laser hole was on the left, the beam returned to nine o'clock, indicating that the mirror and bottom of the unit were closest on the right side. When I turned LaserAlign 180° so the hole was on the right, the beam returned to three o'clock, showing that the mirror and registration surface were closest on the left side. So was it left, or right?
The corresponding aspect of accuracy for zig-align is Total Indicator Reading (TIR), the combination of parallelism and flatness of the module's top and bottom surfaces. The top of the LED tube is lapped flat to 65 millionths of an inch, and no LED module is shipped unless its TIR is 0.0004" or less (0.001") for the ring module.
As seen in The Basics, the accuracy available from repeated images is necessary to obtain the full benefits of lens design. That accuracy also leaves no doubt that all four corners of an image will be in focus at the same time, and reproduction of shapes will be accurate over the entire image.
A laser unit is a slight improvement over spirit levels or mechanical measurement, but it is no match for zig-align. In fact, unless you get into measuring a wave's phase differences that result from splitting the beam and then recombining it, zig-align is more accurate than any laser up to an actual distance of thirty feet. And zig-align offers the combination of high precision, accuracy, simplicity, and ease-of-use – with low price.