Quick Answer
Temperature changes can significantly impact the performance of a scope's reticle, causing it to shift, and its zero to be affected, making it essential to adjust the scope accordingly with every temperature change.
Effects on Reticle Clarity
Temperature fluctuations can cause the reticle’s clarity to degrade, making it harder to aim accurately. This is because the reticle’s materials can expand or contract, causing microscopic shifts in its structure. Typically, this effect is most pronounced in scopes with illuminated reticles, where the temperature change can cause the illumination to become uneven or distorted. For most scopes, this effect starts to become noticeable when the temperature difference is around 30-40 degrees Fahrenheit.
Zeroing and Temperature Changes
When the temperature changes, the scope’s zero can also be affected. This is because the scope’s internal components, such as the erector rod and the lens elements, can expand or contract with the temperature change. As a general rule, the scope’s zero can shift by around 1-2 MOA (minutes of angle) for every 10-15 degrees Fahrenheit of temperature change. To compensate for this, hunters should plan to re-zero their scopes after every significant temperature change, ideally every 20-30 degrees Fahrenheit.
Adjusting for Temperature Changes in the Field
To adjust for temperature changes in the field, hunters can use a technique called “temperature compensation.” This involves adjusting the scope’s elevation and windage knobs to compensate for the expected shift in the zero. Hunters can use a temperature compensation chart, which lists the expected shift in the zero for different temperature changes, to help them make these adjustments. Another option is to use a laser rangefinder or a ballistic computer to calculate the necessary adjustments.
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