How does Objective Lens Size affect Shooting?
It’s time to buy a new hunting scope for your rifle. Maybe you’re having a hard time seeing at night, or just aren’t getting the magnification you want. So, you decide to look at rifle scopes with larger objective lenses. Bigger is always better, right?
Well, bigger may be better in some cases, but in the case of rifle scopes, the size of the objective diameter gets a little tricky. All considerations and explanations regarding objective lens diameter below hold true whether you’re looking at a hunting or tactical scope.
First Things First: Size Designation
When you’re looking for a scope, you’re likely going to see a lot of numbers that define the scope. For example; 4-12×50 mm. The first two numbers in this series show the magnification and power of the lens for variable scopes. In this case, the riflescope has a magnification ranging from 4x to 12x giving it a 3x zoom power (12 divided by 4). A fixed scope would be designated like 6x42mm where the 6 is the specific (fixed) magnification and the 50mm indicates a 42mm objective lens diameter.
The last number is the size designation indicating the objective lens diameter. For this particular scope, the objective lens would measure 50 millimeters. The objective lens is the one in front of the rifle scope. It’s typically the one with the largest diameter. Typical sizes you find on riflescopes range from the ’20s mm to 56 millimeters for the objective diameter.
Another size that is important to know when it comes to image and light quality of a riflescope is the tube diameter. Today’s cheaper scopes have a 1-inch diameter. Higher-end and therefore more capable scopes most often come with a 30mm tube. All optics and lenses are inside that tube and a larger diameter results in larger lenses that impact the image quality specifically in low-light conditions.
For the purposes of this discussion, any lenses measuring 50 mm and higher are going to be considered large objective lenses.
The Human Eye And Hunting Optics
Before we get started talking about whether or not the 50 mm objective lens is going to be good for you, we have to talk about your eyes. Your hunting optics are only as good as your eyes, unfortunately.
The exit pupil.
What is an exit pupil? The exit pupil = scopes diameter mm ÷ the magnification level.
Why does the exit pupil matter to you? The human eye uses the pupil to take in light. A perfect human eye will dilate from 2 mm all the way to 9 mm. Keep in mind this is a perfect human eye. The average middle-aged human eye will only dilate from about 4 mm to 8 mm.
If the exit pupil of your riflescope is greater than the dilation of your human pupil, you will not see a clear picture. You could either see a blurred or dim picture depending on the difference in the exit pupil and your actual pupil.
Why Choose a Large Objective Lens?
There are many benefits to choosing a larger objective lens. If you plan on choosing a large objective lens here are some reasons why you may find the large size of the lens helps you sight your target:
- Long-Range and Extreme Long-Range Shooting
- Low light conditions
- Higher magnification as light diminishes
- More flexible with a larger exit pupil
- Wider and brighter field-of-view (FOV)
- Improved image quality at larger magnifications
One group of people who may find a large objective lens increases the quality of their hunting are people with visual impairments such as lazy eye or optical focus injuries. People who have difficulty focusing will find that a large optical lens will compensate for their body’s lack of focus ability.
If you are choosing a large objective lens diameter, keep in mind, it’s not all benefits. Here are some of the drawbacks that you can find when using a large objective lens diameter.
- Weight and bulk are impractical for hunting style
- Can compromise cheek and weld methods
- Effects proper eye alignment
- May collect more dirt in harsh conditions
- More expensive
- Needs higher mounting rings
Another thing that you should consider when choosing a large objective lens is the size of the objective lens bell. The objective lens bell is the metal housing around your objective lens designed to protect it.
This is often the piece of the scope that causes mounting interference. If you can find a large objective lens with a concave objective lens bell, it may make mounting a scope with a large objective lens easier.
Is a larger objective size always better?
Larger objective lenses are not always the best choice. A scope with a large objective diameter can cause your weapon to become heavy as well as compromise your shooting position and style. Often, these objective lenses cause you to mount your scope farther up on your gun changing the entire balance of the weapon. Smaller scopes typically don’t have this problem.
If you are not hunting in low light conditions or with extreme distances, you probably don’t need a large objective lens. In many daylight hunts and midrange hunts, a medium objective lens is going to be far more effective than a large objective lens.
Glass Quality Matters
Another thing to keep in mind when choosing your scope is that glass quality matters. There are many manufacturers who produce superior scopes with a high-quality glass that can outperform larger scopes with poor quality glass. Many mediums scopes with superior glass coatings designed to minimize refraction will outperform large objective lens scopes.
Your objective lens is one area where cost is going to be a direct determinant of performance. With the advancements of filters and coatings like polarization and anti-reflection coatings, your objective lens may just need higher quality glass instead of larger sizing. If you cannot find a scope with built-in polarization, many companies make polarization filters to fit onto your scope. You would be amazed at how the quality of your sight improves with a light filtration.
What Should You Choose?
In the end, choosing the right size objective lens comes down to your hunting style and your eyesight. If you have poor eyesight and choose to hunt in low light conditions a large objective lens is going to help compensate for your natural deficiencies. If your eyesight is fairly good, you rarely hunt in low light conditions, or you need good cheek and weld positioning; a large objective lens is going to hinder your performance while shooting.
The biggest deciding factor for choosing a large objective lens is most likely the weight. If you are a treck hunter who likes to hike in a few miles carrying a heavy scope in addition to other gear may not be an option. Also, holding a very heavy rifle may be impossible for smaller framed people, women, and children. All of these things should be taken into consideration before purchasing a large objective lens scope.