How zig-align Modules Work

Introduction

In order to picture the simplest alignment pattern, stand in front of one mirror. You see just one repeat. A more useful alignment pattern is made of multiple repeats created between two mirrors.

How zig-align creates alignment patterns

Have you ever stood between two mirrors and tried to see your back? If the mirrors are parallel, you cannot see your back. In fact, your presence even blocks some of the last distinct repeats of other objects. Now picture a small hole in the center of one mirror. When you look through that hole toward the second mirror, you see many more repeated images. The smaller the hole, the more mirror area there is for making repeats.

This is how zig-align creates alignment patterns.

Why zig-align uses two mirrors

Each repeated image doubles the error shown by the previous one, so the "tail" of such a pattern exaggerates even slight error and makes it obvious. These alignment patterns are so sensitive that they can show when the two mirrors, or the planes to which they are registered, are exactly parallel.
In-Depth

Advantages

Alignment patterns should be simple to use and sensitive enough to show you any change in parallelism, no matter how small. This alerts you to sources of degradation in your images, whether or not you are familiar with the equipment you are using. You could just be setting up and learning how it works, or you could be checking equipment that you have been using for years and, perhaps for the first time, finding problems of which you were totally unaware.

Zig-align patterns entice you to investigate problems. They also let you keep track of parallelism routinely and allow you to retain accuracy.

zig-align's two modules

Zig-align produces two distinct alignment modules, the LED module and the ring module. Both modules display parallelism by forming alignment patterns made from repeated images, but they differ in sensitivity and physical appearance.

The original module, the ring module, is a carefully machined round mirror, first available in 1987. Below are examples of the alignment pattern you see through its view hole.

 

 

 

The newer module, the LED module, is much more sensitive and versatile. It has been available since 1991. Below are examples of its alignment pattern.

 


Uses of the LED Module

see information brief: LED angular/axial

 

Module Characteristics and Advantages

LED module:

This module...
  • is constructed so accurately that its top and bottom surfaces can be used interchangeably. This means the module can be used upside down or right side up, registered to any plane (including the paper plane).
  • can be suspended from its top, improving contrast in the alignment pattern and reducing flare. This makes repeated reflections easier to see, especially important at longer distances when the pattern is small. Suspending the module makes it usable on horizontal setups and at any angle.
  • has built-in, battery-powered illumination, so room light is not required.
  • has the potential for dimming the LEDs, maximizing contrast and minimizing flare in the alignment pattern. This permits fine-tuning of pattern brightness to accommodate any viewing situation.
  • contains a custom viewing system so you can see the alignment pattern by looking into the side of the module. This eliminates the need to climb above the module on vertical setups. Because the viewing system is enclosed, it is possible to use both top and bottom of the module.
  • is extremely sensitive, because the four parts of the LED alignment pattern best accommodate the way the human mind-eye system recognizes shapes. This is one reason the LED pattern is easier to use than the ring module.
  • has a more accurate placement of the view hole than does the ring module, so when the pattern is symmetrical, the smallest possible included angle is represented and parallelism is almost perfect.
  • should be handled with care.

    Ring module:

    This module...
  • is made entirely of glass that is accurately machined (reasonable parallelism of glass is assumed but not checked).
  • has one registration surface. For enlargers, it can be used only right side up in vertical setups, and never on the paper plane.
  • requires ambient light.
  • has a small, unenclosed mirror set at 45 degrees to the viewing hole for enlarger systems, so you can view the alignment pattern from the side.
  • uses rings instead of dots to create the alignment pattern, making it 4.5 times less sensitive than an LED module.
  • is permanently mounted in the adapter(s) you need for copy with small and medium formats, so the copy camera can be at any angle.
  • is light-weight and inexpensive.
  • should be handled with care, especially because this module is entirely glass.

    Module Specification Comparison

    This table is linked to the Module Characteristics and Advantages list.

    Click a Description to view details.

    • Description LED Module Ring Module
    1. Parallelism, top-to-bottom of module .0001 to .0004" .0001 to .0010"
    2. Minimum included angle that results in a change in the pattern's shape (when mirrors are 2 feet apart) 20 seconds of arc 90 seconds of arc
    3. Recognition of shape of alignment pattern easier not as easy
    4. Placement of view hole ±.0016" ±.0020"
    5. Room light required? no yes
    6. Orientation on enlargers any angle vertical only
    7. Placement in either plane being checked yes no
    8. Durability* greater less
    * Neither module, if broken, can be restored to original accuracy.

    Click here to view more details comparing zig-align's alignment checking modules.


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