First Focal Plane vs. Second Focal Plane Scopes
By John Childs
First off, to understand the differences between Front Focal Plane and Rear Focal Plane (Also called First Focal Plane [FFP] and Second Focal Plane [RFP or SFP], respectively) scopes, you should understand the basic mechanics of variable scopes.
In a variable scope, there is a main tube, and within this main tube resides another tube called an erector assembly. This tube extends from the power selector ring to just in front of your adjustment saddles. In the erector assembly resides a pair of lenses called erector cells. These cells move closer together or farther apart when the power selector ring is manipulated, effectively changing your magnification.
This is important because it sets up the physical difference between Front Focal and Rear Focal Plane Scopes. In Front Focal Plane Scopes, the reticle is installed on the front of the erector assembly, so as the power selector ring is turned, changing the target magnification, the reticle is magnified proportionally to the target. Simply stated, if you are using a 4.5-14 power scope, and you are looking at a target at 4.5 power, you have magnified the target 4.5 times. On a FFP scope you are also magnifying the reticle 4.5 times. If you change the power to 14, you are now magnifying the target 14 times, and the reticle is also magnified 14 times.
Another way to describe this is that anything IN FRONT of the erector assembly is magnified, while anything rear of the erector assembly is not. This is why I prefer calling the different focal planes either Front Focal Plane, or Rear Focal plane respectively.
The two locations in the scope where the reticles are placed, are also the only locations within the scope where the image resides in focus, BESIDES where it exits the eyepiece. This is why the reticles are placed in these locations, otherwise we wouldn't even be able to see the reticle in the scope.
While it's sometimes said that a FFP scope has the reticle grow and shrink during magnification changes, the reality is the reticle stays the same size in relationship to the target throughout the power range, because it is being magnified at the same value as the target.
Conversely, in a Second or Rear Focal Plane scope (SFP/RFP), the reticle is located in the rear of the erector assembly, so as the magnification of the target is changed, the magnification of the reticle appears to not change.
By John Childs
First off, to understand the differences between Front Focal Plane and Rear Focal Plane (Also called First Focal Plane [FFP] and Second Focal Plane [RFP or SFP], respectively) scopes, you should understand the basic mechanics of variable scopes.
In a variable scope, there is a main tube, and within this main tube resides another tube called an erector assembly. This tube extends from the power selector ring to just in front of your adjustment saddles. In the erector assembly resides a pair of lenses called erector cells. These cells move closer together or farther apart when the power selector ring is manipulated, effectively changing your magnification.
This is important because it sets up the physical difference between Front Focal and Rear Focal Plane Scopes. In Front Focal Plane Scopes, the reticle is installed on the front of the erector assembly, so as the power selector ring is turned, changing the target magnification, the reticle is magnified proportionally to the target. Simply stated, if you are using a 4.5-14 power scope, and you are looking at a target at 4.5 power, you have magnified the target 4.5 times. On a FFP scope you are also magnifying the reticle 4.5 times. If you change the power to 14, you are now magnifying the target 14 times, and the reticle is also magnified 14 times.
Another way to describe this is that anything IN FRONT of the erector assembly is magnified, while anything rear of the erector assembly is not. This is why I prefer calling the different focal planes either Front Focal Plane, or Rear Focal plane respectively.
The two locations in the scope where the reticles are placed, are also the only locations within the scope where the image resides in focus, BESIDES where it exits the eyepiece. This is why the reticles are placed in these locations, otherwise we wouldn't even be able to see the reticle in the scope.
While it's sometimes said that a FFP scope has the reticle grow and shrink during magnification changes, the reality is the reticle stays the same size in relationship to the target throughout the power range, because it is being magnified at the same value as the target.
Conversely, in a Second or Rear Focal Plane scope (SFP/RFP), the reticle is located in the rear of the erector assembly, so as the magnification of the target is changed, the magnification of the reticle appears to not change.
First Focal Plane Vs. Second Focal Plane Scopes
This is a good place to explain subtensions, which are the distances between the reticle marks or stadia lines within your scope. If you are using a duplex reticle, an example of a subtension is the distance between the crosshair and the bottom post. If you are shooting a scope with a mil reticle, the distance between each mil is a subtension.
Subtensions are what really differentiates between the two types of scopes. In a FFP optic, the subtensions will be the same through the entire power range of the scope. If using a mil reticle, and the target is two mils tall at 7-power, it will be two mils tall at 14-power as well. If you were using a RFP scope, and the target was two mils tall at 14-power, it would theoretically be 4 mils tall at 7-power, and if the scope went to 3.5-power, would be 8 mils tall. Essentially, in a RFP scope, the relationship of the reticle to the target doubles as the power is decreased by half.
Why is this important? Because if you are thinking of using aiming features within a scope such as a Mil Reticle, or Ballistic Reticle, these features would only be useable on max power in a traditional RFP Scope (or by doing the math of halving/doubling aspect when the power is changed), but in a FFP scope reticle subtensions are useable throughout the entire power range.
Why would you choose a RFP scope over a FFP version? First off, cost is a major consideration. FFP's as a rule, run anywhere from $500-1000 more in high quality models. This alone can be the deciding factor for many people.
Another factor would be close shots in heavy cover. With a RFP scope set at low power, especially with a duplex reticle, your eye is automatically drawn to the center by the heavy lines, making the reticle easy to find. When using a FFP scope at low power, the reticle is often reduced to an extent where it can be hard to find. Both of these instances are generalizations, because there are reticles in both FFP & RFP scopes that would work very handily in this same scenario.
A third factor, especially concerning long range shooting, is RFP scopes will generally have a much finer crosshair at distance, allowing for much more precise shot placement. Because the reticle does not magnify with the image, the reticle appears smaller against the target. When looking through a FFP scope, the reticle is magnified at the same rate as the target, so at maximum power the reticle is much larger than at lower powers, therefore covering a larger portion of the target.
Again, these are generalizations, because a FFP scope can be made to have just as small a reticle at max power as a RFP scope, but in this scenario, can become almost unusable in the lower power settings, practically disappearing, and often becoming just an aiming point.
Subtensions are what really differentiates between the two types of scopes. In a FFP optic, the subtensions will be the same through the entire power range of the scope. If using a mil reticle, and the target is two mils tall at 7-power, it will be two mils tall at 14-power as well. If you were using a RFP scope, and the target was two mils tall at 14-power, it would theoretically be 4 mils tall at 7-power, and if the scope went to 3.5-power, would be 8 mils tall. Essentially, in a RFP scope, the relationship of the reticle to the target doubles as the power is decreased by half.
Why is this important? Because if you are thinking of using aiming features within a scope such as a Mil Reticle, or Ballistic Reticle, these features would only be useable on max power in a traditional RFP Scope (or by doing the math of halving/doubling aspect when the power is changed), but in a FFP scope reticle subtensions are useable throughout the entire power range.
Why would you choose a RFP scope over a FFP version? First off, cost is a major consideration. FFP's as a rule, run anywhere from $500-1000 more in high quality models. This alone can be the deciding factor for many people.
Another factor would be close shots in heavy cover. With a RFP scope set at low power, especially with a duplex reticle, your eye is automatically drawn to the center by the heavy lines, making the reticle easy to find. When using a FFP scope at low power, the reticle is often reduced to an extent where it can be hard to find. Both of these instances are generalizations, because there are reticles in both FFP & RFP scopes that would work very handily in this same scenario.
A third factor, especially concerning long range shooting, is RFP scopes will generally have a much finer crosshair at distance, allowing for much more precise shot placement. Because the reticle does not magnify with the image, the reticle appears smaller against the target. When looking through a FFP scope, the reticle is magnified at the same rate as the target, so at maximum power the reticle is much larger than at lower powers, therefore covering a larger portion of the target.
Again, these are generalizations, because a FFP scope can be made to have just as small a reticle at max power as a RFP scope, but in this scenario, can become almost unusable in the lower power settings, practically disappearing, and often becoming just an aiming point.
First Focal Plane Vs. Second Focal Plane Scopes
I'm going to fly in the face of much common "INTERNET" wisdom here, but the reality is, if you are dialing your solution, you have no theoretical advantage in using a FFP scope. Both scopes act identically when dialing yardage, and can be shot at any power setting since you are using the center of the reticle.
However, many long range shooters will dial their vertical solution, but want to use hold-off for their windage adjustment. If using a FFP scope, this can be done at any power setting, but using a RFP, this can only be done at max power (There are some exceptions using the ½ power and doubling rule, but that's not the point here.). Another nice feature of a FFP scope is if you miss on your first shot, and if you see the shot through your scope, or have a spotter behind you calling the shot, you can immediately shoot again using hold-off regardless of the power setting you're on.
The rub is that if shooting at very long ranges, most shooters will naturally be at the max power setting. At this setting, shooting hold off is identical for either a FFP or RFP scope. Where the differentiation comes is with mirage, or with exceptionally high-powered scopes. There are times when dropping the power a little bit can be useful, and this is again where the FFP design really shines, because regardless of power, all the subtensions work, and hold-off can be employed for shots. If using a RFP design, you must either shoot at maximum power if using hold-off, or dial your solution.
Another feature commonly touted for FFP scopes, is their ability to range. While this is absolutely correct, a few comments need to be made here. First, if you are using a reticle to range something, especially if it's at long range, you're going to be at maximum power so you get the most reliable read as possible on the target. If you're at maximum power, either the FFP or RFP scope is going to work identically. The FFP can range at any magnification setting, but why would you sacrifice the ability for the better measurement by not being at max power.
Second, in today's world, serious long range shooters are going to be using a laser range finder, so this takes the entire discussion about ranging ability right out the window.
While this all may seem like I'm in favor of the RFP scope, you have to look at what you're truly using your optic for. For my long-range guns, I do run FFP scopes, and it's primarily to be able to shoot hold off. I don't want to have to think about whether or not I'm on max power, or to have to double-check the magnification setting when it's time to be pulling the trigger. I want to be able to concentrate on getting a good solution, dialing my elevation and then using hold-off for my windage with whatever my ballistic program spits out as my hold. Being able to shoot hold-off is the number one reason for employing a FFP optic.
I use a RFP scope for the majority of my walking/mountain style rifles. This is where they excel, especially considering I don't plan on shooting beyond about 500 yards. While a FFP scope would work here, they are generally heavier and cost more, which doesn't make sense on a rifle I don't plan on shooting ultra long ranges with, but will carry many miles each day.
So to summarize, decide what the main use of your rifle is going to be, and pick an optic that's appropriate. Are you going to be a long-range sniper type (FFP), or are you more of the CQB kinda guy (RFP)? Pick the scope that best fits your budget and the style of shooting you plan on employing, and go get it done
However, many long range shooters will dial their vertical solution, but want to use hold-off for their windage adjustment. If using a FFP scope, this can be done at any power setting, but using a RFP, this can only be done at max power (There are some exceptions using the ½ power and doubling rule, but that's not the point here.). Another nice feature of a FFP scope is if you miss on your first shot, and if you see the shot through your scope, or have a spotter behind you calling the shot, you can immediately shoot again using hold-off regardless of the power setting you're on.
The rub is that if shooting at very long ranges, most shooters will naturally be at the max power setting. At this setting, shooting hold off is identical for either a FFP or RFP scope. Where the differentiation comes is with mirage, or with exceptionally high-powered scopes. There are times when dropping the power a little bit can be useful, and this is again where the FFP design really shines, because regardless of power, all the subtensions work, and hold-off can be employed for shots. If using a RFP design, you must either shoot at maximum power if using hold-off, or dial your solution.
Another feature commonly touted for FFP scopes, is their ability to range. While this is absolutely correct, a few comments need to be made here. First, if you are using a reticle to range something, especially if it's at long range, you're going to be at maximum power so you get the most reliable read as possible on the target. If you're at maximum power, either the FFP or RFP scope is going to work identically. The FFP can range at any magnification setting, but why would you sacrifice the ability for the better measurement by not being at max power.
Second, in today's world, serious long range shooters are going to be using a laser range finder, so this takes the entire discussion about ranging ability right out the window.
While this all may seem like I'm in favor of the RFP scope, you have to look at what you're truly using your optic for. For my long-range guns, I do run FFP scopes, and it's primarily to be able to shoot hold off. I don't want to have to think about whether or not I'm on max power, or to have to double-check the magnification setting when it's time to be pulling the trigger. I want to be able to concentrate on getting a good solution, dialing my elevation and then using hold-off for my windage with whatever my ballistic program spits out as my hold. Being able to shoot hold-off is the number one reason for employing a FFP optic.
I use a RFP scope for the majority of my walking/mountain style rifles. This is where they excel, especially considering I don't plan on shooting beyond about 500 yards. While a FFP scope would work here, they are generally heavier and cost more, which doesn't make sense on a rifle I don't plan on shooting ultra long ranges with, but will carry many miles each day.
So to summarize, decide what the main use of your rifle is going to be, and pick an optic that's appropriate. Are you going to be a long-range sniper type (FFP), or are you more of the CQB kinda guy (RFP)? Pick the scope that best fits your budget and the style of shooting you plan on employing, and go get it done
