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When it comes to gearing up for your hunt this season, there are many things to consider: weapon of choice, caliber/gauge, decoys, camouflage clothing, calls, etc. However, one thing always seems to raise the most questions, and coincidentally it can be the most important purchase you make that can directly affect the success of your hunt: optics.
Few things can improve your odds of bagging your trophy of a lifetime like good glass, but not all glass is created equal. That being said, what separates a $1500 scope from a $100 scope and everything in between? Manufacturers will use certain buzzwords such as: eye relief, fully-multi coated, light transmission, exit pupil and a slew of other words; but what do these terms mean and how do they help you choose what is best for you? Once you understand these buzzwords, you can easily determine what features you need to make your scope work for you.
The first thing you are likely to encounter when looking at scopes is something to the tune of 3-9x40 or 4-16x50. What do these numbers mean? Read out loud, this would sound like "three to nine by forty" or "four to sixteen by fifty".
The first part of the equation is what is called the magnification; and on a 3-9x40 scope, the magnification on this scope can be adjusted from 3 power to 9 power, and anywhere in between. Setting the scope to 3 power, means that your target will appear to be 3 times closer to you than it actually is, and at 9 power, it will appear 9 times closer to you. In raw numbers, something at 100 yards away would appear to be 33.3 yards away at 3 power, and 11.1 yards away at 9 power.
Another important thing to consider is the magnification range, which is calculated by dividing the maximum power of the scope by the minimum power. A 3-9 power scope has a 3x magnification range, whereas a 4-16 scope has a 4x magnification range. There are now scopes with as high as 8x magnification ranges. The higher the magnification range, the more versatile the scope can be, but it also comes at a price.
The second part of the equation (40 on a 3-9x40 scope) is the measure of the objective lens (the one you don't look into, at the front of the scope) in millimeters, and all other factors being equal, a larger objective lens will allow more light to enter the scope, which usually results in a brighter picture.
Things to consider:
Average shot - It is very easy to over magnify your gun. Most whitetail deer are shot under 100 yards, so a scope powered above 9 power is not only unnecessary, it can become a hindrance.
Bigger isn't always better - If 40 is good and 44 is great, it would stand to reason that 50 or more is even better, but that's not always the case. A larger objective lens forces you to mount the scope higher to allow the bell of the scope to clear the barrel. This works against you in two-fold, first because the farther away the scope and the bore are, the less accurate your gun will be; two, your cheek weld on your rifle stock will be compromised from having to lift your head to be able to see through your scope.
Eye Relief/Exit Pupil
The next thing you are likely to notice when looking through a mounted scope is the eye relief. Eye relief is simply the distance your eye needs to be from the scope where you can see a full picture. Most standard rifle scopes will have eye relief up to about 4", which means your eye can be as far as 4 inches away from the scope and still see a full picture. Any farther, and you will begin to see a black shadow/ring around the outside of your picture inside the scope, conversely if you get to close, you risk hitting yourself in the face with the scope when your gun recoils after firing. Shotgun/muzzleloader scopes can have eye relief up to 6", which helps accommodate for the extra recoil associated with these firearms, but we will discuss later at what cost this comes.
Exit pupil is a term that the majority of people have almost no clue what it is, but is a very crucial part of purchasing optics. Exit pupil is quite literally the size of the picture that enters your eye. A healthy human eye can dilate up to about 7 millimeters (sometimes more), and aged eyes may only be able to open to 4 millimeters or less. Exit pupil is measured in millimeters, and is calculated by dividing the size of the objective lens in millimeters by the magnification power. A scope with a 40 mm objective set at 3 power, will produce an exit pupil of about 13.3 mm, which is more than adequate for transmitting as much light/picture as possible to the eye. Conversely, the same scope, set at 9 power, will produce an exit pupil of about 4.44 mm, which is going to produce a relatively smaller, darker picture.
Things to consider:
Bigger isn't always better (Part II) - If 3" of eye relief is good, and 4" is better, 6" should be great. Once again, not always the case. The farther away you get from your scope, the more your field of view suffers. You want to be far enough away that you don't hit yourself, but not so far that you can't see anything but a pinhole through your lens.
But sometimes, bigger is better - It's hard to go wrong with more exit pupil. No matter how good your glass is, if the picture getting to your eye is tiny, it will appear dark and tough to see. Overpowering your scope can drastically reduce your exit pupil, and the last thing you want during that golden hour of last light is a dark picture.
Light Transmission/Lens Coatings:
Contrary to popular belief, scopes do not "gather" light, rather they transmit it. The finest (and most expensive) scopes can have light transmission ratings nearing about 98%. Great scopes will transmit up to 95% light, but the majority of scopes transmit somewhere around 90% of light that hits the objective lens. Unfortunately, not all manufacturers will list their light transmission rating, and there isn't an accepted standardized measuring system, so not all transmission ratings are created equal.
Light transmission is largely a factor of coatings on the lenses. It seems silly, but these microscopic coatings put on the lenses are what can separate a $500 scope from a $1500 scope. Coatings can do many things, from reducing glare, or waterproofing and fogproofing the glass, to phase correction which aligns the different color spectrums as they move through the lenses. The more coatings added, the more expensive the scope. You will also hear four terms when describing how the coatings are applied to the lenses: coated, fully coated, multicoated and fully multicoated. Coated is the lowest grade, and it means that there is at least one coating on one lens surface. Next is fully coated, which means there is one coating on all air to glass surfaces. The next two are the most frequent options. Multicoated means there are multiple layers on at least one lens and as you can probably guess, fully multicoated means there are multiple layers on all air to glass surfaces.
Things to consider:
Go big or go home - In today's market, there is no reason to purchase any optic that is not fully multicoated, even budget friendly scopes are available in fully multicoated options.
The majority of scopes on the market in the United States will have a 1" main tube. In recent years, long range shooting sports have increased the demand for scopes using a 30 mm tube, and in some very specialized cases, tubes up to 34 and 35 mm.
The importance behind tube diameter comes when you understand how scopes are built. Inside the main tube of the scope lies another tube, called the erector tube. The erector tube is an obviously, smaller tube, which houses some lenses and your reticle, and is how elevation/windage adjustments are made. When the adjustment turrets on the side and top of your scope are turned, they press on this erector tube and move it inside the scope. When you "run out of adjustment" in your scope, what you have actually done is pushed the erector tube as far as it can go in one direction. However, if you have a bigger outside tube, you can increase the amount of adjustment available in your scope, which is decided advantage when shooting at longer ranges where "doping your scope" is required.
Things to consider:
Bigger can be better - I would guess that 95% of rifle scopes on the market still carry a 1" main tube, and it has served very well, and will continue to do so, especially in most hunting applications. However, for those looking to stretch their shooting a little further, depending on manufacturer, a 30 mm tube usually offers about 20 MOA (20 inches at 100 yards) more adjustment than a comparable scope with a 1" tube.
Next to exit pupil, this is far and away the most misunderstood term in optics, but it happens to be one of the most important ones to grasp. Simply put, parallax is an optical illusion.
Consider this: you are driving down the road and look down at your speedometer, and your needle is centered directly over 60 mph. If a person sitting in your passenger seat looks over, it will likely appear to them that the needle is somewhere around 58 mph, because they are looking at it from a different angle. The needle didn't move, the numbers behind it didn't move, so what happened? Parallax.
Parallax in a scope is the same concept, if I were to lock a scope down in a vise and aim it at a point on the wall, any distance away (the further away, the more obvious it becomes). With my eye centered behind the scope, moving my head side to side would make it appear that the crosshairs moved off of my target. Once again, the scope didn't move and the target didn't move, but if I was shooting, my point of impact would be off. Quite simply, my scope and my target are not operating on the same plane, and I need to adjust my parallax on my scope to get them working together.
On most scopes, parallax adjustment is fixed at 100 yards, which is usually fine for most hunting purposes. If your head happens to be slightly off at 100 yards, your point of impact may only shift less than an inch or so. However, for those who frequently shoot longer ranges, there are scopes that offer some sort of parallax adjustment, which is either found on the front of the scope around the objective lens, or a third dial on the left hand side of the scope. Either of these is usually easily distinguishable because it will have numbers, usually starting at 25 and ending at infinity, which are associated with the range of your target. To use these, all you have to do is establish the range of your target, dial your parallax to match, and you should reduce and possibly eliminate any perceived crosshair movement due to change in head position behind your scope.
Things to consider:
Average shot - Once again consider your average shot. Having a parallax adjustment can't hurt, but like any features, you will pay more to get it. If you aren't going to be shooting over 200 yards anytime soon, a parallax adjustment is probably not necessary. However, if you plan on routinely shooting over 200 yards, and especially if you plan on doing so from different shooting positions, parallax adjustment is an absolute must.
It stands to reason that as a consumer, you would want to have the best of all the features. However, as we all know, this is usually not possible. Optics are no exception, and most questions regarding features can be answered by consulting what is called the optics triangle. The optics triangle references three key features: magnification, eye relief, and field of view. Every scope has these three features, but they are all in direct correlation with each other. If you increase the magnification of your scope, you have to decrease the eye relief and the field of view, and so on and so forth. The closer you get to one feature, the more you rob from the others. Sometimes, magnification is the most important necessity (long range, prairie dog hunting). Other times, eye relief is more important (shotgun/muzzleloaders). The important thing to consider is that changing one directly affects the other two.