Tuesday, July 8, 2008

Scope features, mounting and zeroing



Quality is the most important aspect when choosing a scope. A scope well made of highest quality components is always worth the extra money it costs compared to inferior quality scopes.
Good quality control alone costs money. But it’s worth the extra investment as the result is a better performing scope that should last you for years.
Many things affect both quality and price of any scope. These include the type of glass used, eyepiece design, precision taken in grinding, polishing, and centering the glass interiors, the type of anti-reflection coatings, the sharpness and contrast of the whole optical system.
Important issues to consider include the material the tubes are made of, the type of construction of the tubes, single or multiple piece, the way the lenses and reticules are mounted and kept in place, how well the tube is sealed against the elements, the capability of all internel components to handle recoil and the external finish of the scope is always to be kept in consideration.
In most situations the brand name is a guide to quality. Manufaturors like Leica, Leupold, Nikon, Schmitt und Bender, Swarovski, Weaver, and Zeiss all have a reputation for high quality optical products. Other companies like BSA, Bushnell, Simmons, and Tasco have a reputation mainly on low budget scopes. As a rule you get what you pay for.


Scopes are usually described by their magnification. Sometimes a second number is provided, eg 4x28 or 3-9x36. The first digits refer to the magnification, and the second is the diameter of the objective lens.
Magnification may be fixed, or variable between a low and higher value, as in 3-9x or 4-12x. 4x means the scope magnifies four times closer than it does with the naked eye.
Magnification also affects brightness. The higher the power, the dimmer the view. Magnification also affects the field of view of the scope. The greater the magnification the smaller the field of view.
Everything is magnified when you look through a scope, including your own shakes. The higher the magnification, the harder it is to keep the target steady. 2, 3, or 4 power scopes are easier to sight through if the rifle is hand held. Higher powered scopes often result in blurred views unless it is a top quality scope.
Magnification also affects the size and weight of the scope. Usually a scope with higher magnification is longer and heavier than a scope with less magnification.

Objective lens

The second number most commonly associated with scopes points to the diameter of the objective lens in millimeters. So in 4x32 the 32 means that the front lens of the scope is 32mm in diameter.
The diameter of the objective is essential as it controls how much light the scope can let in, and finally transmit to your eye. The bigger the objective lens, the more light the scope absorbs. A large objective lens makes for a larger and heavier scope. A 40mm objective lens is the largest normally required for Field Target, even for high magnification riflescopes. Low and medium power scopes will do very well with objectives of 20mm to 35mm.

Main tube diameter

The standard main tube diameter for most scopes is 1" (25mm).
A 1” main tube scope has enough internal windage and elevation adjustment range for all normal purposes. Scopes with 1" tubes are lighter than scopes with 30mm tubes, which is always an advantage.
The idea behind a larger main tube is for more efficient internal light transmission. These scopes are also usually equipped with "syrup bucket" objective bells. Big scopes undermines the handling qualities of the rifle and should be avoided unless really necessary.
Consider a scope with a 30mm tube only if the rifle is being set-up specifically for hunting in full darkness.

Light transmission

Light transmission affects how much light gets through the lenses inside a scope and out towards your eye. It is influenced by the type and quality of the glass used, the anti-reflection coatings, and control of glare inside the scope.

Exit pupil

The magnification of a scope determines the size of the exit pupil. The size of the exit pupil determines how much light is transmitted to your eye. The exit pupil can be seen by holding the scope at arm's length and looking through the eyepiece. The pencil of light you see is the exit pupil.
The diameter of the exit pupil is calculated by dividing the diameter of the front objective lens in millimeters by the magnification of the scope.
The diameter of the exit pupil does not really matter as long as there is enough sunlight so that the pupil of your eye is smaller than the exit pupil of your scope. But when sunlight light gets dim, and the pupils of your eyes enlarge, the exit pupil of your scope may become the limiting factor.

Field of view

The field of view is the area you see through your scope. This is measured in degrees.The larger the field of view the more area you can see through the scope. A big field of view is very important at close range when out hunting moving animals.
Since field of view is measured in degrees, the closer the shooter is to a target, the smaller the actual area he sees through his scope. Field of view is inversely proportional to magnification. For these reasons someone who may have to shoot at for example a rabbit needs a lower power scope because it provides a bigger field of view.
If using a variable power scope, keep it set at low magnification for maximum field of view when out hunting.

Eye relief

The term "eye relief" refers to the distance from the scope's ocular lens to the eye. For scopes to be mounted on springer piston air rifles or pre-charged pneumatics a 3”-3.5” eye relief is more than enough.

Contrast and resolution

These are the most recognized optical specs of any scope. Resolution is the sharpness of a scope. A scope with good resolution can resolve fine details. Contrast is the crispness, and ability to distinguish one object from another. Together they primarily determine how clear things are observed through a scope. Good design, premium quality optics, good lens coatings, good internal flare suppression, precise assembly, and good quality control usually result in a scope with high resolution and contrast.


The parallax refers to the apparent movement of the target relative to the reticule when you move your head as you look through the scope. Parallax can only be eliminated from a scope at one range, although it is not usually apparent in normal use unless there is something wrong with the scope. All Field Target scopes come with an adjustable objective that can be adjusted to eliminate parallax at specific the distances needed to knock down a target.
To minimize the effect of parallax, always mount an optical sight as close to the barrel as possible.

Lens coatings

Most optical sights have magnesium-fluoride anti-reflection coatings on their air to glass surfaces. These coatings assist light transmission. These are what produce the blue, red, or green reflections you see when you look into the objective lens of a scope.
Be aware of how the scope is described as anti-reflection lens coatings. Coated means the glass surface has a single layer of anti-reflection coating on some lens elements, usually the first and last elements. The only ones you can see. Fully Coated means that all air to glass surfaces are coated. This is good. Multi-Coated means that at least some of the surfaces, usually the first and the last lenses have multiple layers of anti-reflection coatings. Fully Multi-Coated means that all air to glass surfaces have multiple layers of anti-reflection coatings. Multiple coating layers are more effective than a single layer. Always for Fully Coated or Fully Multi-Coated scope.

Focusing a telescopic sight

The idea is to focus on the reticule, not some object in the distance. To focus a scope, set it to its highest power and go outside. Point the scope at a blank area of sky. Turn the ocular bell housing until the reticule appears to be perfectly sharp. Tighten the locking ring and your scope is focused to your eye. You will not have to change it unless your vision changes.

Fixed magnification scopes

Fixed magnification scopes have great advantages when compared to variable power models. In scopes of the same quality and maximum magnification, a fixed power scope is optically superior. It is also simpler in design and construction, and therefore more durable. The fixed power scope is easier to seal against water and dust. It is usually lighter and more compact than a variable power scope. Fixed power scopes are less expensive than equivalent quality variable power scopes. For all of these reasons a fixed power scope may be a better choice than a variable power scope, depending on the application of course.

Variable power scopes

The great advantage of variable power scopes is the freedom they give the shooter to select a larger field of view or greater magnification, depending on the situation. This is an enormous asset on a dual purpose rifle, or an all-around rifle. The shooter who shoots only at close range, or who always shoots at long range, has no real need for a variable power scope.
Variable power scopes almost always perform better at the low to medium power settings than they do at the highest settings. Since the front objective of a variable power telescopic sight cannot enlarge to let in more light as the magnification is increased, the view gets dimmer as the magnification goes up. This is because the exit pupil gets smaller.


Over spend, but don't over buy. This contradictory sounding advice is actually pretty good. What it means is, buy the very best quality optical sight you can afford. But don't buy more magnification, light grasp (objective lens size), weight and bulk than you actually need. The same applies to mounts. Spend your money on solid, high quality mounts. Whatever magnification or type of optical sight best fits your needs, if you buy top quality sights and mounts you will not be disappointed.


The first thing one has to decide before mounting a scope is to determine which type of mounts to set up on your air rifle. Mounts are usaully made as a two piece and a one piece in three heights. Low, medium and high. Quality of the mounts are also very important. Make sure you choose only good quality mounts for your air rifle.

Two piece mounts are generally mounted on pre charged pneumatics (PCP).

One piece mounts are mounted on spring piston air rifles.

Low mounts are usually set up on a rifle with a scope with a small objective lens. For Field Traget shooting, a scope with a bigger objective lense is mounted, usually up to 50mm, and medium height mounts are used. Scopes with an objective lens over 50mm, a high mount is the norm. Try to use the lowest possible mount to keep the scope as close as possible towards the barrel. Time to put the mounts on the air rifle.

On this spring rifle, there are two parallel dovetail grooves with three scope stop holes between them. Select one of these three holes for the scope stop pin on the rear mount.

Step 1 : Attach the scope rings to the rifle.

Most recoiling spring piston air rifles have three stop pin holes. Put the stop pin of the rear scope ring in the one that seems best to you. The pin's purpose is to stop backward movement of the scope rings and of the scope itself. Airguns that don't recoil don't need a scope stop. Remove the top caps of the ring before installing them on the rifle. The reason for this will be shown in the next step. Snug the rings so they don't move, but don't tighten them all the way yet.

Step 2. Position the scope.

Lay the scope on the open rings and position the eyepiece by sliding the scope back and forth. You may have to move one or both rings to get this right. Position the rings so the scope's eyepiece will be the correct distance from your shooting eye when the gun is held naturally. This is usually between two and three inches from the eyepiece lens, but it is the spot at which the image in the scope appears as full and bright as it gets. To see what this looks like, move your head back and forth along the stock, as you look through the scope with both eyes open. Then, position your head on the cheekpiece where you want it to be and move the scope back and forth until the image appears bright and full. Now put the top caps back on each ring without moving the scope forward or backward. Tighten them until the scope is held secure but can still be rotated with your hand.
Step 3. Align the scope's vertical reticle.
Align the vertical reticle with both eyes open and the gun held naturally to your shoulder. Rotate the scope until the vertical reticle seems to bisect the gun perfectly. Now you can tighten the base of the rings securely to the gun.
Step 4. Tighten the top caps to hold the scope.
This is a step where care should be taken. There is no need to over-tighten the ring caps to hold the scope in place, but most people overdo this part. Tighten each screw partially, then move to the next one and go around the pattern of screws many times, rather than tightening each screw all the way on the first try. You will put even tension on the caps and be less likely to dent the scope tube this way. If there are two screws on the side of the ring, tighten only one, then tighten the one on the opposite corner of the other side of the cap. Leave the other two screws for the moment and tighten two screws on the other ring next. Then come back to mount one and tighten the two screws you left loose. Then back to the other ring and keep rotating until the scope is secure. It takes less tightening that most people think. Keep going around the pattern, tightening very little each time. Hold on to the small end of the Allen key to keep from over-tightening. Some try to get the same amount of space between the caps on either side of the mounts, but don't worry about it very much. Once the screws are tight the job is finished. Now the scope can be zeroed.
Once you have your scope fixed securely to your rifle, you can begin the process of zeroing in your scope.

With your target set up, a plain target with a centre bull is enough, you need to decide at what range you want your rifle to be zeroed in at. Most air rifle zeroing is done at 30 or 35 meters. Zeroing is preferebly done on a bench with rests to minimize movement as much as possible whilst shooting.

To start, shoot three shots at the bullseye of your target. If your shots group, for example, low and to the left, then the adjustments you need to make on your scope are high and to the right. Make the necessary adjustments via the turrets on the scope. The turret on top is for elevation and the one to the right is for windage. On the elevation turret you will clearly have marked which way to turn to go higher or lower. Same thing goes for the windage turret, right or left. Fire three more shots, to see what effect the adjustments you have made have had on the impact point. Keep making minor adjustments until you are satisfied that the impact point is the same as where you are aiming. This is a trial and error process.

Sometimes you find that your scope has run out of adjustment before you have achieved your zero. In this case you will have to do what is called shimming the mounts, in order to give yourself more adjustment. When shimming, first set the adjusters to their mid positions and then remove the scope from the mount rings, and if the rifle is shooting low, you will need to add a shim or two to the rear scope ring. The most common material used for shimming is negative film. This can be cut into strips wide enough to lay at the bottom of the mount and you will probably need to use no more than three shims in order to give yourself the necessary adjustment back in order to obtain zero. It is important not to have the adjusters at their full extent of travel, as this can restrict the amount of movement that the other adjuster will allow.
Once you have achieved zero at the range required, your scope should hold this until adjusted again. Put any adjuster caps back on the scope, to protect your settings.

It is pointless to have someone zero the scope for you since each person shoots differently and you could have someone zero it for you but it may be of no use to you at the end, because of different eye relief and shooting style. There is no substitute for getting to know your gun and scope combination, and this starts with assembling it all together and zeroing it in. You are the one who is going to shoot it, so you must be the one to set it all up.

Happy shooting!!!!

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