How The Size Of Objective Lens Affect Shooting

So you have been hunting or shooting at competitions for a while? Do you know how an objective lens affect you?

The objective lens is the lens that is featured on the front of the rifle scope. It’s the lens that is closest to the target being viewed. There are multiple options when it comes to objective lenses and all have different calibration. For example, 3-9X40mm represents the specifications of the scope. 3-9X represents the scope’s magnification levels and 40mm is the diameter of the objective lens.

Is the size of the objective lens a factor when shooting?

objective lens


Light makes it possible to get accurate shot whether you are hunting or participating in competitive shooting. One of the core purposes of an objective lens is light gathering. Whether you are adroit at shooting or not, there is no way you can take an accurate shot without clearly viewing the target.

An objective lens gathers enough light to give you a vivid and bright picture of your target. The size of the lens determines the amount of light the scope gathers. A bigger objective lens allows more light to be transmitted through the scope. However, this is dependent on some mitigation factors. To get a better understanding, let us first understand how the eye works.

The eye pupil has the capability to shrink and grow so as to enable the eye to detect light as necessary to see. In total darkness, the diameter of the exit pupil of a normal eye has a diameter of 7mm. This diameter is wide enough to enable you to see better and enhance your night vision. On the other hand, during the brighter days, the diameter of a normal eye is 2mm, the diameter reduces to keep you incredibly comfortable throughout the day.

For optimal light gathering efficiency, the functions of the scope’s exit pupil should match those of the eye’s exit pupil. The magnification of the rifle scope affects both the objective lens size and the exit pupil. To get the size of the exit pupil of the scope, you can use the following formula.

The diameter of the scope (mm) divided by the magnification level is equal to the size of the exit pupil.

For example, let’s say you are hunting using 2-10X40mm. when the sun begins to go down in the evening you may want the size of the exit pupil to be above normal (8) to make the targets a little brighter. The magnification level should be set at 5 so as to get the size of the exit pupil to 8mm, i.e. 40mm (diameter of the scope) divided by 5 (magnification level) is equal to 8mm (size of the exit pupil).

With the idea in mind, it’s easy to see that large objective lenses are powerful enough to gather more than enough light. This can be quite uncomfortable unless you attach a proportional magnification level to the rifle. In addition, if you match a small objective lens with a lot of magnification your sight picture will become dim and dark.  From this, we can deduce that a bigger objective lens might not be the best.


Beyond what your eyes can see there comes a number of challenges when a larger objective lens is used. A large objective can be defined as a lens with a diameter bigger than 42mm, that is 50mm and up.

The first issue is the cost-effectiveness of large lenses. A rifle scope with a large objective lens will be more expensive in comparison to the scopes of similar quality. Moreover, they are heavy which means they make the rifle uncomfortable when shooting.

A bigger objective lens must be mounted farther and higher from the barrel. This is a disadvantage since it limits the overall precision and accuracy of the rifle scope. Besides, it makes it difficult for broad adjustments. Additionally, if you do not have a special adapter, mounting the scope higher will make you lose a proper cheek weld.


All is not gloom with larger objective lenses. They are highly effective at shooting the fixed long-range target. Besides, larger objectives lenses are perfect for hunting when the sun is going down or during night time.


If you are a novice it’s not advisable to start with large objective lenses. A lens size of 40mm or 42mm is ideal for most shooters or hunters. You have to take into account some compromise when choosing an objective lens to suit your needs.

Smaller would be proper for scope crafted for low magnification or close-range shooting. Going larger is always a perplexing proposition, and with regard to the benefits versus disadvantages of a large scope, you may want to stick the smaller one.

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