Focal Planes Explained

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I frequently see a lot of discussion with regard to focal planes. People often misunderstand what they are, how they work, the differences between them, and which is really appropriate for their specific use. Lets start by discussing what we mean by focal plane and what the differences between them are. When we talk about a magnified optic’s focal plane, we’re discussing whether the reticle is located in front of the magnification assembly or behind it. First Focal Plane, or FFP, would refer to the reticle being etched on the glass first in line behind the objective lens at the front of the scope, and in front of the magnification assembly. Second Focal Plane, or SFP, refers to a reticle being etched just ahead of the ocular lens at the rear of the scope, and behind the magnification assembly.

Focal Plane Location

The location is important because it determines a large difference between the two. A Second Focal Plane scope, with the reticle located behind the magnification assembly, will have a reticle appear to be the same size across the magnification range. That is actually an illusion. The target is being magnified, and the reticle appears to be a constant size. In actuality you are changing the relationship between the size of the target and the size the reticle is expressing in one of two angular adjustment methods.

Second Focal Plane scopes have a reticle that is only valid at one point across the entire range of magnification, and it is usually the highest. So for example, Nightforce makes a 3.5x-15x scope in both Second Focal Plane and First Focal Plane varieties. On the Second Focal Plane model, the reticle, expressed in Minutes of Angle, MOA, or Milliradians, MILs, is only valid at 15x. So if you were to take a shot at a target and miss by 1 Mil to the right, that measurement the scope is giving you is only valid at 15x. If you were to dial down to 7.5x you would effectively double what that same 1 Mil hash mark is representing. Think about it. You reduced the size of the target by half, yet the reticle is the same size. So if you were to measure the same miss on paper, it would appear to be about one half mil to the right now. It isn’t.

The bullet didn’t miss farther because you were at a different magnification setting. The bullet doesn’t care if there’s a scope on the rifle at all. You just changed the scale on the reticle by reducing the magnification. The good news is you can still use the reticle to correct for a miss. Even though at 7.5x the miss looks like it’s a half mil to the right, and it really is a full mil, you can still hold a half mil left at 7.5x and score a hit if the wind remains constant. The downside is, that correction is only valid for you.

Focal Plane Advantages

This is where a First Focal Plane scope, being located in front of the magnification assembly, starts to shine. On a First Focal Plane scope using the same example, a miss to the right of 1 Mil at 15x is correct. Dial down to 7.5x and you will notice the reticle appears to shrink in size along with the target. What’s really happening is you have reduced the magnification of the target and the reticle. The relationship between them is constant.┬áSo an object viewed through a First Focal Plane scope appears to be the same size in relationship to the reticle across the enitre range of magnification, not just the maximum settings. The advantages here for tactical rifle shooting are numerous.

G2 Reticle on a Bushnell ERS at 3.5x

G2 Reticle on a Bushnell ERS at 3.5x

G2 Reticle on a Bushnell ERS at 21x

G2 Reticle on a Bushnell ERS at 21x

Let’s keep the same example for simplicity. If I miss by 1 Mil to the right at 15x, I just hold 1 Mil left to correct for that miss at 15x. I can do the same thing at 7.5x, or 12, or 4x, or anywhere in the magnification range. If I missed by a Mil, I hold a Mil in the opposite direction. “You said you could do that with a Second Focal Plane Scope too!” Yes and No. I said you can still adjust using the reticle in a Second Focal Plane scope anywhere in the magnfication range, but the measurement won’t be correct. The reason that is significant is because if I throw you a curve ball and say take a shot at this 500yd Target, on 6x power, and I want you to hold 1 Mil to the left, what do you do? Can you do the math in your head to figure out what 1 Mil really looks like at 6x on a second focal plane scope? Wouldn’t it be easier to just hold that 1 Mil to the left?

Focal Plane Reticle Significance

This difference illustrates the major capability differences of first focal plane and second focal plane scopes. Now I won’t tell you that first focal plane scopes are perfect. Since the reticle grows and shrinks with the target, you can find yourself in a situation where at the lower end of the magnification range the hash marks on the reticle are difficult to see. The manufacturer can make them larger and more useful at lower magnifications. The problem is also true in reverse. If you have hash marks on a first focal plane scope that are easily discernible at low magnification, they will grow very large on the opposite end of the spectrum obscuring more of the target and the surrounding area. So what is the solution? Good reticle design.

A well designed reticle will work well all along the magnification range and all it takes is some forward thinking and good planning for the differences. An excellent example is the G2 reticle designed and developed in the Bushnell Elite Tactical series of rifle scopes by the owner of GA Precision, George Gardner. That’s actually what the G2 stands for, George Gardner. I’ve seen that man shoot at competitions and he is every bit the spectacular shot at a rifle competition as he is spectacular working on rifles. What Mr. Gardner did was create a kind of hybrid reticle.

The G2 reticle has a very fine center of the crosshair so at higher magnification levels you can still see the target and make a precise shot. That allowed him to make the other parts of the reticle, and hash marks, a bit larger and more useful at lower magnification levels. It really is an excellent reticle. It is not the only one on the market, it is however, an easy example. If the manufacturer takes the differences into account you can easily have your cake and eat it to. Go back to Nightforce, the original MLR reticle was difficult to use at lower power settings because the hash marks were difficult to discern. Nightforce tweaked the design, and released the MLR2.0. You can see the differences.

Nightforce MLR Reticle

Nightforce MLR Reticle

Nightforce MLR2.0 Reticle

Nightforce MLR2.0 Reticle

Bushnell G2 Reticle

Bushnell G2 Reticle

Wrapping Up Focal Plane Discussion

There is nothing wrong with second focal plane scopes. I’m not trying to say that there is. Second focal plane scopes are exceedingly popular with target shooters and the hunting crowd for good reasons. Those scopes typically are cheaper to produce and thus cheaper and more affordable to purchase. The constant reticle size also obscures less of the target. If you are planning to take a single shot at an animal inside a few hundred yards, the benefits of a first focal plane scope are neither necessary nor especially useful. The same is true of target shooting at known distances where time is plentiful and field of view is important.

First focal plane scopes really excel in dynamic environments. Situations that have shooters using different magnification settings for different shots followed in close succession where time is not a commodity. For tactical rifle matches, they are the clear choice. MIL/LE marksman use them for the same reasons. You need to be able to use the reticle at any magnification and know the measurements and reticle scale are valid. Especially if working with other shooters. If shooter number one takes a shot and hits at 600 yards, he can give his wind call to shooter number two, saying, “Use half your 10mph full value wind,” and shooter number two can use that to score a hit. This even works across different calibers and it can be done on any magnification setting with a first focal plane scope.

Owner and Proprietor of AccuracyTech, LLC. Rich is a Firearms Enthusiast, Precision Rifle Competitor, and Writer. He is committed to bringing readers quality reviews and articles related to the Precision Shooting Sports. If you have any questions for him, please use the contact form on the site.

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