- Magnification numbers
- Objective Lens
- Fixed Power Vs. Variable Power
- Reticle / Crosshair
- Bullet drop compensation
- Light transmission
- Eye Relief
- Field of View
Magnification numbersIf you've checked out any of the rifle scopes either online or in a store yet then you'll have noticed that they all start with numbers that look something like this 3-9x40 or some other numbers with the same format ie. #-# x #. The number range of 3-9 is your magnification ability. So for example, in a scope which has a magnification range of 3-9, this means you are able to magnify and enlarge your target starting at 3 times it's size, up to 9 times it's size. 3 being your low power and 9, your high power. There are many different ranges you can find when it comes to rifle scope magnification, but bigger isn't always better. Rather than purchasing a rifle scope based on a larger magnification range and thinking that if you get something with a larger magnification ability, the better off you'll be, decide first what you plan to do with your rifle. There's no point in spending extra money on a feature if you're not going to use it. But thinking long term is also a good thing. Personally, I decided on a scope with a 3-15 magnification power because I plan to go hunting, but I can also see myself getting into precision rifle shooting in the future and if I'm spending a good chunk of change on a high quality optic, if possible, I'd like it to be a multi-purpose use optic.
Objective LensThe objective lens is the lens found at the end of your scope (the one you look into is called your ocular lens). The 40 from 3-9x40, refers to the diameter of the objective lens and is in millimetres. The larger this number, the larger the lens itself is. When choosing the size of your objective lens an important consideration will be when you plan to use the scope. Will there be low light or will it be used only during the middle of the day when there is plenty of light? The larger the objective lens, the more light can be transmitted which can help to make a clearer image in lower lighting situations. The larger you go with your objective lens however, the heavier it will be and if you are going hunting and trying to pack light, this may not be the most practical. You'll also find yourself needing higher mounting scope rings which could potentially be harder to find and it can also affect your cheek and weld method causing you to either need an adjustable cheek rest, or a stock specialized for your firearm to allow for more comfortable shooting. If you don't plan to be shooting during dawn or dusk when light conditions aren't as ideal, then you can get away with a smaller objective lens. Majority of scopes out there are between 32 and 44 mm.
Fixed Power vs Variable PowerWe've already discussed the magnification numbers, but we only discussed the variable power. There is also something called fixed power, this means that there is no range of magnification on that particular scope. An example of this would be 4x32. This means that the scope has the 4 power magnification or having the target appear 4 times its typical size. There is no adjustment option for this. As with anything, there will pro's and con's with one option vs another. One of the pro's of a fixed power scope is that there is less fiddling around with magnification as it's already done for you. This provides a level of assurance in not having to worry about making a mistake in your magnification adjustments and then missing your target. It's also going to cost less which is great if you have a fixed budget. Possible con's are that because the magnification is fixed, you aren't able to adjust it to a target further away or that may be closer. For this reason variable scopes can be more desirable. Another pro to a variable scope is that it can ultimately be used anywhere because of the ability to adjust your magnification.
Reticle / CrosshairThe reticle or crosshair is the point in which the vertical and horizontal lines meet up to make a cross or "+". This is the aiming point. There are many variations of reticles including, but not limited to fine crosshair, duplex crosshair, german reticle, target dot, and mill-dot. A consideration is the reticle's focal plane. The reticle will either be located at the front focal plane, also known as the First Focal Plane or FFP. Or it can be located at the rear focal plane, also known as the Second Focal Plane, or SFP. The difference is that with the SFP, the reticle will remain a constant size whether the target grows larger due to increased magnification, or shrinks due to decreased magnification. If you purchase a FFP, the reticle will increase with magnification, or decrease with lower magnification. Second Focal Plane scopes are not as expensive as those that are First Focal Plane, but depending on what type of shooting you plan to do, it may be worth wile purchasing one on the FFP. Wether you buy a scope that is FFP or SFP will depend on your personal preference, and again, what you plan to do with your rifle. Because I'm looking at getting into longer range precision shooting and I like that the reticle size increases with magnification, I felt the FFP would be a good choice for me. But purchasing a FFP scope may not be the best option for you if all you plan to do is go shooting at a max of 100 yards.
Bullet Drop CompensationSome rifle scopes have a bullet drop compensation (BDC) feature, this can also be referred to as ballistic elevation. This is actually something that's built in to your reticle and it compensates for the effect of gravity. In order for this to be accurate, it needs to be specifically tuned for the particular ballistic trajectory of a particular combination of gun and cartridge at a predefined muzzle velocity and air density. Nikon has created the SpotOn technology which allows you to go to their website, input the type of scope you have, followed by the bullet size, manufacturer, grain amount, bullet style, weight, and how far you're shooting, scope magnification and it will show you where to have everything lined up on your reticle. It's pretty cool, but keep in mind that this doesn't account for windage.
Light TransmissionThis is the rifle scope’s ability to transmit available light and give a bright and sharp image. Factors that can affect brightness include objective lens diameter, magnification, type and quality of the objective lens glass and the type of lens coatings.
Eye ReliefEye relief is the space between the ocular lens and where your eye is placed. This is important in order for you to prevent 'scope eye'. This occurs when you don't have proper eye relief and your scope hits the area around your eye from the firearms recoil after a shot and can be pretty painful. Eye relief also plays a role in preventing eye strain and ensuring a clear view. The amount of eye relief you need is dependant on the firearm you have as well as the magnification of your scope. The more powerful a firearm, the more recoil, then the more eye relief distance you'll need. That said, the higher the magnification of your scope, the less eye relief you will need. Typically 4 inches is the average eye relief distance needed.
ParallaxParallax occurs when your reticle and the target don't line up within the scope and can create an unclear sight picture. You can spot this by moving your eye or head around whilst peering into the scope; if the reticle moves around the target you're aiming at, then you are able to confirm that it is a parallax issue you're dealing with. More on this and how to fix it below in the section on adjustments.
Field of ViewField of view (FOV) simply put is the area which you can view through your optic. As you increase magnification, the field of view decreases. FOV is mеаѕurеd in feet at 100 yards. To explain, if a rifle scope states that the field of view is 42ft at 100 yards, that means you can view a 42 foot scene from left to right at 100 yards. For scopes that have a variable magnification power you'll likely find a range for the FOV, for example, 41.2-8.6 ft/100 yds. This accounts for the magnification variation which if it were 5-15 then at 5 power you'll see a scene of 41.2 across and at 15 power you'll see a scene of 8.6ft across.
AdjustmentsThere are many adjustments which can be found on a scope. These include the following:
Windage and ElevationWindage is the horizontal adjustment on your scope whereas Elevation is the adjustment of the vertical direction.
ParallaxThese adjustments are made when parallax is an issue. This is done in steps; obtain your sight picture by aiming at your target, then adjust your parallax until the reticle becomes clearer. You want it as clear and crisp as possible. Then, while lifting your cheek off the stock of your firearm, continue to look through your scope lens. Look around and see if the crosshairs move off target when you do. If they do, continue to adjust until they stay focused and centred on your target, even when you move your eye around. Once there, lock these into place.
IlluminationIllumination adjustments can be useful in controlling the level of brightness, especially when in low light conditions as it increases the illumination intensity for the lit parts of the reticle/crosshairs.
MagnificationThis adjustment is exactly like it sounds, allowing you to adjust your level of magnification (provided you have a variable power and not fixed) with the given range of magnification power on the rifle scope you have.
DiopterThe Diopter adjusts focus of the reticle, this is not to be used to focus on an object. While it will focus on the object, you don’t want to because it will effect the focus of the reticle, which is on another plane.
Stare at a blank blue sky or single colour wall, bring the scope up and quickly look through. Don’t stare, your first glance is what you are looking for, then take the scope away, adjust the diopter. Repeat. Until the reticle is crystal clear. Your eye very quickly adjust focus so you want the reticle clear at a relaxed eye focus at a neutral object so your eye has only one thing to try and view. Then you use your parallax adjustment to reduce parallax which, typically brings your target into focus.
LensesTypically, you'll find about eight lenses on a rifle scope (this includes the obvious ocular lens and the objective lens), however there can be more, or less.
CoatingsMajority of scopes will have some sort of coating on the lens and near all rifle scopes are fogproof and waterproof. The coatings available will vary and typically, the more coatings you have, the more expensive the rifle scope will be. Coatings can provide a clearer and brighter sight picture as well as reduce glare, but having multiple coatings doesn't necessarily mean that it will be better than one with a single coating; this will depend on not only the coatings but also the glass quality. There are 4 types of coatings commonly found on rifle scopes, these include the following:
- Coated - This means there is a single layer coating on at least one of the lens surfaces.
- Fully Coated - This means that there is a single layer of coatings on all air to glass surfaces.
- Multicoated - This means that there is more than one layer of coatings on at least one lens surface.
- Fully Multicoated - This means there are multiple layers of coatings on all air to glass surfaces.
ConclusionThis information should give you a good basis of understanding to be able to determine what type of rifle scope you'll be looking to purchase. However, if you are looking for additional information, I'd definitely recommend listening to The Silvercore Podcast, more specifically, these episodes:
- Ep. 15: Insider Pro Tips from Jimmy Hamilton of Vortex Nation
- Ep. 16: Firearms, Optics and Equipment for New Hunters
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