Have you ever looked through a scope expecting to see a crisp, clear scene, only to be greeted by fuzzy crosshairs or the image of an animal so badly out of focus it was hard to tell whether you were looking at a small whitetail deer or a large cottontail rabbit? Or, just as disturbing, have you ever had your scope perfectly on target, only to have the crosshairs move when you shifted your eye slightly off-center from the axis of the scope’s eyepiece? If so, welcome to the world of improperly focused telescopic sights, where the severity of such problems can range from inconsequential (low-powered scopes with only eyepiece focusing) to extremely serious (high-powered scopes with both eyepiece and objective-lens focusing). How bad can it get?
Recently, after intentionally using an incorrect focusing procedure on an impeccably good 3.5-15×50 riflescope with an adjustable objective, I got 10 inches of parallax at a distance of 300 yards and 24 inches at 500 yards. To create such horrendous parallax, all I did was set the objective-focusing/parallax adjustment for 50 yards and refocus the image for long-range viewing by using the eyepiece-focusing mechanism. Can such focusing errors occur inadvertently? You bet, and all too easily.
1. WHEN A SCOPE IS FOCUSED PROPERLY
A correctly focused scope is one in which both the reticle (crosshairs) and the target image appear perfectly sharp–reticle sharpness is the result of proper eyepiece focusing, whereas target sharpness is the result of proper objective-lens focusing. An incorrectly focused scope is one in which either the reticle or the target image or both appear fuzzy.
All telescopic sights have some means of eyepiece (ocular) focusing, the only legitimate purpose of which is to make the reticle appear sharp to the viewer’s eye. Using the eyepiece-focusing mechanism to sharpen the target image (which is possible) will result in the reticle looking blurry. Moreover, eyepiece focusing is incapable of changing either the scope’s parallax-free distance or its Point of Aim (POA).
2. TYPES OF EYEPIECE FOCUSING
There are two types of eyepiece focusing: American and European. With American-type eyepieces, a correct focus is achieved by screwing the entire eyepiece housing either backward or forward on fine threads until the image of the reticle appears perfectly sharp, at which point the housing is secured in place with a lock ring. The lock ring can be loosened without tools by grasping the eyepiece housing with your hand and rotating it counterclockwise away from the ring. European-type eyepieces are easier to use but less secure. They are focused by rotating a “fast-focus ring” located at the end of the eyepiece.
3. WHY FOCUS AT ALL?
The first step in eyepiece focusing is to determine if it is needed. Begin by pointing the scope toward a plain background, such as the sky or a light-colored wall. If the reticle appears very sharp and very black, it is properly focused and no adjustments are necessary. If the reticle looks fuzzy or otherwise indistinct, go to step 5.
4. HOW TO NAIL THE FOCUS
With the scope pointed toward a plain background, rotate the focusing adjustment counterclockwise (backward) until the reticle appears to be very unfocused. Then rotate the adjustment clockwise (forward) until the reticle appears perfectly sharp. The reason for starting with the eyepiece in a rearward position and focusing as it is moved forward is to prevent your eye from accommodating (using its own focusing mechanism) as the point of sharpest focus is approached. Even then, you might have to repeat the process once or twice in order to get the focus perfect.
If your scope has only eyepiece focusing, your focusing chores are done–at least until your vision changes or some inconsiderate oaf tampers with the mechanism. But if your scope also has a focusable objective, you must go to the next step.
Regardless of what you call the mechanism that makes it happen, objective focusing and parallax correction are two sides of the same coin. Unlike eyepiece focusing, which should be used only to make the reticle appear sharp, objective focusing simultaneously performs two very important functions: 1) superimposing a perfectly sharp image of the target on the scope’s reticle; and 2) eliminating parallax at the target distances you specify.
5. OBJECTIVE FOCUSING ADJUSTMENTS
As was the case with eyepiece focusing, there are two distinct types of objective-focusing systems: the traditional adjustable objective (AO) and modern side focusing. An adjustable objective consists of a focusing ring located on the scope’s objective bell that moves the entire objective lens assembly either forward or backward so that the image of the target falls precisely on the reticle. A side-focusing adjustment consists of a knob located on the left side of the windage and elevation turret that moves an auxiliary lens back and forth within the scope tube to accomplish the same end. Side focusing is more user-friendly in that the knob is easier to reach from a shooting position.
6. DIFFERENT WAYS, SAME RESULTS
Having identified your scope’s objective-focusing mechanism, you now have the option of adjusting the focus either by referring to the yardage/meter numbers printed on the ring or knob or by directly observing the target image as it comes into focus. To effectively focus by number, you must determine the correct target distance, preferably with a laser range finder, before aligning the number with the index mark. To focus visually, simply adjust the mechanism until the target image appears perfectly sharp, along with the reticle.
To use scopes with adjustable objectives without focusing, simply set the parallax-free distance at either 100 or 150 yards. This will let you shoot quickly and with sufficient accuracy for big game at any range.
KEEP IT CLEAN
There is a right way and a wrong way to clean the lenses of your riflescope. Start with the proper cleaning materials. You’ll need a retractable lens brush, liquid lens cleaner, commercial lens tissues, cotton-tipped applicators and microfiber cloth. These supplies should be stored in a resealable plastic bag when not in use.
Use the lens brush to safely whisk away dirt and dust particles. Apply a small amount of the the cleaning liquid to a lens tissue or cotton-tipped applicator and wipe the lens surfaces using a circular motion, beginning at the center and working toward the edges. For a quick cleaning, simply moisten the lens surfaces by breathing on them.
Dry the lens surfaces by wiping them gently with lens tissues or the dry ends of cotton-tipped applicators–never with a shirt or handkerchief. Finish by polishing the lenses with the microfiber cloth.
With one eye closed, point your finger at a small object located several feet away. Holding your finger still, move your head from side to side and notice how your finger appears to move laterally relative to the object. This optical phenomenon, called “parallax,” also appears in improperly focused telescopic sights as an apparent movement of the reticle relative to the target image when the eye is moved from side to side in the scope’s exit pupil.The illustrations below show two ways parallax can occur. The first shows the image of the target, formed by the objective lense, falling in front of the reticle. The second shows the image falling behind the reticle. And the third shows a parallax-free image. The viewing distance determines the target-image position within the scope. The good news is that scopes with adjustable objectives can eliminate parallax for any particular distance by focusing the objective so that the target image falls precisely on the reticle.Scopes with fixed-focus objectives are permanently adjusted by the manufacturer to be parallax free at a specific distance: either 100 or 150 yards/meters for centerfire riflescopes and somewhere between 50 and 75 yards/meters for rimfire, shotgun and muzzleloader scopes. Unless defective, such scopes won’t have more than about 1 inch of parallax at any reasonable shooting distance.