Reticle Subtension

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Focal Planes Explained - image NRA American Rifleman
Focal Planes Explained - image NRA American Rifleman

Q: I have a Zeiss IV 4-16x50 scope which has a MoA 2 second focal plane reticle. Each hash mark measures 2 MoA at 16x. My question is: set on 12x would it measure 1.5 MoA and 1 MoA at 8x?

Shane Brand

A: In your Zeiss scope having the reticle located in the second focal plane is an advantage but also a disadvantage. Range subtensions are given for each hash mark at maximum power, but even though the reticle is in the second focal plane, you can still find the range it will hit when set on other magnifications. Bear in mind, however, that at longer ranges there is almost a 5-percent error between inches and MoA. This is because one minute-of-angle at 100 yards is actually 1.047".Assuming that elevation and windage adjustments are in 0.25" MoA and subtensions of the hash marks is 2 MoA at 16x, you might choose 8x where the subtension will be 4 MoA. On 12x it should measure 3 MoA.

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