Select the Right Tool for the Job
A lot goes into selecting the right optic for your firearm, and one of the first questions that’s often asked is “Front focal plane or rear focal plane?” The answer lies in how you’re going to use your system. Don’t let armchair operators fool you, neither focal plane is better or worse than the other – it’s merely a matter of selecting the right tool for the job at hand.
Before you make your decision, it’s important to know what we’re talking about, so here’s a crash course on focal planes. In every riflescope there are two locations that a reticle can be installed at. Those locations are your focal planes, and one or the other will serve as the housing area for your reticle. For simplicity’s sake, the location closer to the objective lens is referred to as the Front Focal Plane (also known as First Focal Plane), whereas the location closer to the ocular lens is the Rear Focal Plane (also known as Second Focal Plane) - refer to the graphic below.
Inside the erector system (which is a tube inside of the scope that controls the magnification), there are a pair of lenses called erector cells. These lenses move forward and backward as you manipulate your power selector ring, causing the image you’re seeing to either shrink or grow. The erector cells magnify and de-magnify anything that is in front of them – this is how magnification in a scope works.
Naturally, this is what creates the difference between how the reticle looks in a Front Focal Plane scope compared to a Rear Focal Plane scope. If you’re using a Front Focal Plane optic, the reticle is placed before the erector system (magnifying lenses), so when you zoom in, the reticle is magnified along with the image. If you’re using a Rear Focal Plane scope, the reticle is before the erector system, so all of the magnification happens after your eye sees the reticle, which means the reticle will stay the same size no matter what magnification you're on. That, by and large, is the most significant difference between the two options. But what does it mean and how can you apply it?
Front Focal Plane
Because the reticle magnifies with your image, in a Front Focal Plane scope the Mil/MOA lines on the reticle will be accurate throughout the entirety of the magnification range. So, if you’re utilizing a Mil-based reticle, a Mil hash mark on the reticle will equal a Mil whether you’re at 5x or 25x magnification. This allows you to use accurate holdovers at any given point.
Rear Focal Plane
Because the reticle on a Rear Focal Plane scope always stays the same size, the subtensions will only be accurate on one specific magnification – typically your maximum magnification. So, again, if you’re using the same Mil-based reticle as above, you’d need to be on 25x for your Mils to be accurate for holdover shooting. Any less than that and you’ll have to do some quick math in order to get an accurate holdover point. At half-magnification, your Mil would really be two Mils, as your image has become half-size in relation to your reticle – which, again, never changes in Rear Focal Plane - refer to the graphic below.
Which focal plane you require depends entirely on how you’re going to be using your rig. A Front Focal Plane optic is ideal for a shooting style that we’ll call “hold-off” and is popular among long-range shooters. The concept is simple: You hold high for elevation and hold left or right to compensate for wind, using your Mil or MOA reticle appropriately. As your reticle grows with magnification to match your target, those holdover points don’t change. So if you’re hunting in open country or planning on regularly ringing steel from a prone position at significant ranges, having those firm hold-off positions is useful. The downside is that the reticle will not be as visible on low magnifications, so if you're shooting on 3x most often, the reticle will be harder to see.
Conversely, if you’re hunting thick country or in a situation where you’re likely to engage your target at a close-range, a Rear Focal Plane optic – which offers a large field-of-view and a bold, usable reticle at low magnifications – would serve you better.
Ultimately, there’s not a right or wrong answer to the focal plane debate. It’s about selecting the proper tool for the job, same as you evaluate your rifle and ammunition offerings before making a purchase. Take some time to consider what you’re going to be using your rifle for, and you can’t go wrong.