Rifle Scope Repair

Ever since I started using my Dad’s binoculars decades ago, my passion for optical lenses has grown tremendously. I got to experience clear and detailed views of objects that were so far away, and this experience got my attention.


There have been incredible improvements in scope technology ever since Hans Lippershey made the first telescope back in the 17th century. These improvements in technology have led us to the present-day optical systems of rifle scopes. The first rifle scope made by Morgan James and John Chapman around 1835. These early scopes had low optical power and no adjustments for height or windage. Over time, rifle scopes have become very powerful and convenient to use.

The Reticle

Early reticles were basic materials such as horse hair and spider webs. In the mid-1800s etched reticles were first produced, first by hand and then later by chemical etching. The outline of these reticles was more defined thus producing finer detail. The development of Photographic etching then improved the reticles tremendously, and is now commonly used in the latest scopes. Laser etched style reticles are very common in modern scopes today. Reticles can collect microscopic particles floating in the tube thereby obscuring the field of view. They can also be affected by temperature changes. That being said, the detail and information that we can obtain from the modern reticle is excellent.


Significant improvements in lens development have taken place over time. The introduction of multi-coatings and changes in glass work have been some of the main factors for the improvements. Today, the physical properties of light transmission, even in poor lighting, have significantly improved. We have also experienced improved observation angles, longer eye relief, etched reticle systems, and illuminated reticles. Parallax disorders can now be elevated and controlled easily. All these developments have made rifle scopes more functional and helpful.


Most people, when buying a rifle scope, gather crucial information regarding the scope, such as its light gathering capabilities, reticle type and ease of use. Many people, however, do not get to know that their scopes have nitrogen in them
When warm air hits a cold surface, for instance, a lens, it condenses and forms tiny water droplets. It is okay when the condensation happens on the outside of the glass, but when it is on the inside of the glass, it causes fogging.
This is where nitrogen comes in. Nitrogen is an inert gas and is heavier than air. When mixed with less than 1 PPM H2O it becomes denser and thus less susceptible to temperature changes. Also, pure nitrogen has less water content than air and is, therefore, less likely to cause corrosion. This is why nitrogen is used to prevent moisture damage to the coated lens surface.
There are various ways for manufacturers to inject the nitrogen into the tube. One of the ways is to draw nitrogen via a vacuum line and into the tube and then putting the gas under pressure. Once the required pressure has been attained, the tube is then closed up tight. As long as the tube is airtight, the nitrogen will remain in the tube for a reasonable period. The under-pressure gas also forces any microscopic particles onto the inner tread walls of the tube.
When subjected to temperature changes, scopes consequently lose pressure due to expansion and contraction. In fact, I have seen very few scopes in the 30 years I have been repairing scopes, that still have their nitrogen seal airtight.
Both the inside and outside of scopes are exposed to temperature changes. We do have ways of preventing further damage from already present moisture. One of these ways is silica gels that come packed in a container or a small bag. The fact that moisture and scopes don’t work well together cannot be stated enough.

Never Spray Oil on Your Scope

Many scope owners instinctively spray oil into the tube to prevent it from rusting. This is highly discouraged. As I have mentioned, there are very few scopes with airtight nitrogen seals, especially the ones that have been used for quite some time. If your scope is showing signs of rust, then it probably does not have a nitrogen tight seal. Spraying oil into the tube or other parts of the tube (e.g. windage and elevation adjusters) can cause damage to the interior of the scope. A combination of moisture and oil can damage the lens set inside of the scope, and it is advisable to have your scope checked if you suspect this has happened. This will avoid further damage to the scope.

Windage and Elevation Adjustment

Turning the windage and elevation adjusters once in a while is recommendable in order to expose the components to some movement because the grease inside turns hard due to a lack of mobility. For you to return them to the central position, count the number of turns you do either right or left, and then do the same number of turns in the opposite direction. Depending on the quality of the scope, you may have to do a bore sight before using it. Some manufacturers install an opposing spring to compensate for the adjustment. The spring weakens over time because of consistently being subjected to pressure. I recommend that you back off the windage/elevation adjuster if the scope is to remain unused for long periods.

Cleaning Lenses

If you notice particles or dirt on your lens, do not clean it with your handkerchief. Instead, gently blow the lens with your mouth or preferably by the use of a puffer brush. Particles on the lens, if not removed, can cause minute scratches on the lens coating which with time can alter the refractive order of the lens.
After you do the preliminary cleaning, finish with gently spraying isopropyl alcohol (lens cleaner) on the lens, which removes any film or grease. When walking through the woods, cover the it with the lens cap to help stop dirt from getting onto the lens. The lens cap also prevents direct sunlight from entering the tube thereby preventing heat buildup.


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