If you are a hunter – or you just like to shoot – then chances are you’ve heard the phrases “First Focal Plane” (FFP) or “Second Focal Plane” (SFP) when talking about scopes. What does it all mean? What is a focal plane, and why are there two of them…?
The modern shooter will often prefer to use a variable-powered scope. This allows them to have a greater field of view at lower to mid range magnifications, and to really focus in on a given target at higher magnifications.
Most traditional scopes use a Second Focal Plane (SFP) design. This means that the reticle – or pair of crosshairs – is placed further back in the scope, closer to your eye. What that will end up looking like to the shooter, is just a simple magnification of the image beyond the scope. For instance, a second focal plane scope with Minute of Angle (MOA) hashmarks/sub-tensions will simply make your target grow and shrink as you zoom in and out. Those MOA sub-tensions will remain the same size to your eye, because the scope is magnifying the image beyond the reticle. In other words, the sub-tensions in the reticle will not remain on the same spot on the target when adjusting your magnification.
A scope with a First Focal Plane (FFP) design, on the other hand, has the crosshairs further forward in the scope tube. In this case, adjusting the magnification will result in a reticle that appears to grow and shrink with the target. In fact, the sub-tensions will actually remain on the same position on the target at any magnification.
I have illustrated the concept below (not to scale):
You will notice that the SFP scope does not scale the reticle when adjusting the magnification. Therefore, if you would hold one MOA – one hashmark – over your target at 200 yards at 15 power, that same hold-over will not be accurate at any other magnification. This is because the MOA sub-tensions only represent 1 MOA (~1 inch at 100 yards) at full power only.
On the other hand, you can see that with the FFP scope, our reticle does in fact scale with the target, and any hold-overs we know to be accurate at full magnification, will be equally as accurate at lower powers. Again, this is because the reticle sub-tensions will remain in the same position on your target, no matter the magnification. In the case of a FFP scope, the MOA sub-tensions will really represent 1 MOA at any magnification.
To put it simply, a First Focal Plane (FFP) scope will have the reticle scale up or down with your target while changing magnification, in order to keep the sub-tensions accurate at any power, whereas a Second Focal Plane (SFP) scope will keep the reticle at the same size, meaning the sub-tensions will only reflect their measurements at full power.
It goes without saying that this concept of first focal plane would have no effect on a standard duplex/crosshair reticle that you will find in many traditional hunting scopes. Additionally, first focal plane is not limited to the minute of angle measurements, but is actually just as – if not more – common in scopes that utilize MRAD (Mil Radian) measurements.
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