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Which might be right for your rifle: first focal plane (FFP) or second focal plane (SFP) optics? As is often the case, it comes down to your specific situation. Here is a basic primer on FFP vs SFP to help you make a more informed decision.
FFP and SFP Defined
In a first focal plane optic, the reticle is built into the front of the tube, on the opposite end of the magnification from your eye, so the reticle zooms in and out with your magnification.
In a second focal plane optic, the reticle is in the back of the tube, between your eye and the magnification. The reticle is always one size – so if you're below max or above minimum magnification, the reticle measures will not scale along with the magnification.
How FFP and SFP Affect Reticle Scaling
In an FFP, such as the Primary Arms GLx 4-16x, as you dial magnification up, you zoom into the reticle, and as you minimize magnification, the reticle shrinks as well. Any measurement within the reticle, such as mil, BDC points, or a full-on Christmas tree grid, will be true to measure on a first focal plane optic, regardless of where you are within the magnification span. The reticle changes size to maintain its points of measure being true to scale at varying magnification levels.
In an SFP, such as the Kahles K16i 1-6x LPVO (low power variable optic), the reticle looks the same whether you look through it at six or one power. The reticle may be designed to be accurate at the lowest or highest setting, so if you’re at four power trying to utilize this reticle at a distance, the measures within the mil grid will not be true to size.
When Do You Need Reticle Scaling?
But how often are we shooting a 1-6 power optic on anything less than six power where we would also need the mil measurements? We're talking about 400-plus yards away in terms of a target before we need to use the mil tree. Frankly, we'll be dialed to six power when doing that. Reticle scaling really isn’t necessary for this optic.
Now contrast that with a different type of optic, such as the Primary Arms GLx 4-16x. To assume I might need the mil holdovers even if I'm not dialed all the way up to 16 power on that optic is perfectly reasonable. Perhaps we might be at 10, 12, or 14 power and still need to be able to use the mils effectively. We might be shooting to six or seven hundred yards at that level of magnification. The higher the scope magnification and the wider the magnification range, the higher the likelihood of needing a first focal plane optic.
If we use a precision rifle optic, something like a 5-25x, the odds of being dialed to 25 power are almost none for 95% of what we do with that gun. We'll probably be between 12 and 18 power most of the time we're using that optic, shooting out from zero to a thousand. We need a first focal plane reticle because we need the measures to be correct within that magnification span.
Why Not Always Use FFP?
Now, you might be asking, well, why not then just always have a first focal plane? That way, if you happen to shoot something like a 1-6x at four power, you would still be able to use the mil measurements correctly. This comes down to the second main consideration: how the reticle looks.
When you're using a reticle in a first focal plane optic, it's been our experience that the reticle is usually designed with a bias either towards enhanced magnification or less magnification, meaning the reticle looks better and more usable at one end of the spectrum or the other. If we have a reticle that looks great on the low end of the spectrum, it may look overly thick when we move to the top end of the magnification spectrum. It may not be precise, and the same could be true in the other direction. If it looks great at the top end of the spectrum, the reticle and the crosshair might look too thin and hard to track on the low end.
That is true on something like LPVOs. It is routine to see reticles that are nice at one power in a first focal plane body, but as you dial them up, they look thick and chunky when you get to six or eight power. Therefore, they are easy to shoot and track, but when you shoot a distance, the reticle is extremely chunky and covers large portions of your target. And then the inverse is true, whereas if you have a reticle that looks good on target, let's say at six or eight power, the reticle is too fine and can be hard to track for up-close, run-and-gun-style shooting, especially through recoil or snapping the gun up on target.
Cost
While this isn't a hard rule, it is generally true that second-focal-plane optics tend to be more affordable than their first-focal-plane counterparts, so that might be something to consider as well.
Final Thoughts
Suppose you are shooting with a medium to high magnification optic, such as 2-10, 3-12, 4-16, or 5-25. It will likely be routine for you not to be dialed to max magnification yet want to utilize the mil grids or the measurements within the reticle. As such, you want a first focal plane optic.
If you use an LPVO, the answer is much more split down the middle. Plenty of people are shooting second focal plane LPVOs and utilizing them very effectively. You're probably on max magnification when shooting a distance where you need your reticle measurements to be true to scale.
We hope these considerations help your choice, and until next time, we'll see you on the range.
--9-Hole Reviews
