Second- and Third-Axis Sight Adjustment.
Moving forward, we'll cover each of the remaining features and then discuss how to maximize your sight's effectiveness. Finally, I'll tell you exactly how I set up my personal sight and why.
1. Bright pins (fiber optic)
2. Bubble level
3. Ability to shoot out to (at least) 60 yards without any adjustments (multiple pins--five or more)
6. Ability to aim spot-on at any given distance (with a "floater" pin or a "slider")
7. Second- and third-axis adjustability
8. Gang adjustment
9. Ease of adjustment (individual pins, gang adjustment and "floater" pin)
10. Low weight
All About Axes
If you think back to your high school physics class, you may recall there are three axes of rotation: lateral, longitudinal and vertical. These axes are perpendicular to one another and all meet in the center. When discussing bow sights, rotation around each of these axes is referred to as the first axis (rotation around the lateral axis), second axis (rotation around the longitudinal axis) and third axis (rotation around the vertical axis), respectively.
To help visualize these axes, think of the three ways an airplane can rotate. In aeronautics, rotation around the lateral, longitudinal and vertical axes is referred to as roll, pitch and yaw, respectively. Roll is the airplane rotating from its nose to its tail. Yaw is the airplane turning left or right. Pitch is the airplane diving or climbing.
Essentially, the only two axes we need to worry about when dealing with archery sights are the second and third axes.
Adjusting the second axis is merely rotating the sight head on its longitudinal axis. (Think of rotating a dial on the front of a safe left or right.) If you're using a 5-pin sight and are adjusting the second axis, you're merely rotating the sight to the left or right to align the row of pins (the heads of the pins) in relation to the bowstring. You can line them up perfectly parallel with the bowstring, or you can align them so they are canted to the left or right of the bowstring.
It is very important to remember that your bowstring and bow do not have to be perfectly vertical at full draw in order for you to shoot well. However, your line of pins (or your sight bar, if you are using a slider) must always be perfectly vertical at full draw. In other words, your pin heads must be perfectly vertical when the bubble is centered in your level. Second-axis adjustment allows you to cant your bow at full draw, if that position is more comfortable for you.
The sight's third axis is the rotational movement of the sight's head (and its bubble level) around the vertical axis. When at full draw, the bubble level should be exactly perpendicular to your line of sight. The level should not angle toward you or away from you; if it does, this slight angle will throw your bubble level off when you shoot uphill or downhill.
Because many shots at Western big game involve steep angles at long distances, the ultimate Western sight must have third-axis adjustment. The steeper the angle and the farther the shot, the more critical this adjustment becomes. If you are a Western bowhunter hunting in steep country, your sight must have third-axis adjustment, and it must be calibrated perfectly.
Many high-quality sights offer third-axis adjustment. If a sight offers this feature, it is usually advertised on the packaging or the product's website.
The actual adjustment takes place either out near the sight head or at the level itself. Typically, you adjust a couple of setscrews to place the sight solidly in its new position.
Imagine for a moment that your sight head, and therefore your level, is angled so that the left end of the level is closer to your eye than the right end. This will not affect your accuracy when you're shooting on level ground because your bubble level will still read true, but if you aim up or down, the bubble level will not read accurately. In our example, the left end of the bubble is closer to your eye than the right end. So, if you aim sharply downward, the left side of the level will be higher than the right, causing the bubble to move to the left.
In order to make the bubble move to the center, you must cant the bow to the left. This will cause you to miss to the left. When you shoot uphill, the opposite will occur, and you will miss to the right. So, improper third-axis adjustment can cause very serious left or right misses. The farther the shot and the steeper the slope, the greater the error.
Caption: A sight's second-axis adjustment allows a bowhunter to cant the bow left or right, if that position is more comfortable. Field Editor Randy Ulmer likes to cant his bow to the right while shooting. In this image, you can see that his sight pins are vertical, and the bubble is in the middle of the level, even though the bow (and thus, the bowstring) is canted to the right.