With SFP scopes, the relationship between the target and crosshair will change when the magnification is altered. Reticle shown: MTC AMD
Of course, the centre point of the crosshair should not, in theory, deviate when the magnification ring is rotated, although it often does on the cheaper scope models! However, if you use multi-stadia crosshairs like the MTC SCB2 to allow for ‘holdover’ or ‘holdunder’, then you must be aware of this target/crosshair relationship change. It is therefore best practice to familiarise yourself with the aim-point/trajectory relationship by only shooting on a specific magnification, like 8x.
This begs the question: “Why choose a SFP vari-mag scope, then?” Well, a zoom magnification feature is still a very handy feature to have, perhaps for spotting purposes where higher powers allow you to seek out a clearer sight picture. And many shooters also like to use SFP reticles for ‘bracketing’, where ranges can be estimated after having predetermined what distance the gaps between reference points equate to at each of the scope’s magnification settings. Although it requires some initial working out, reticles like MTC’s SCB2 and AMD can provide a very practical method of quickly estimating (or checking) range while taking aim.
First Focal Plane (FFP)
Sometimes referred to as ‘front focal plane’, FFP scopes are usually more expensive by virtue of their more complicated construction, where the crosshair is placed in front of the lens group that determines the scope’s magnification.
In the case of variable magnification scopes (eg: 2-12x or 4-16x), this first focal plane position means that the size of the reticle will appear bigger or smaller, in line with the target image, as the scope’s magnification is zoomed in or out. Therefore, with graduated crosshairs, the relationship between the aim-point references on the reticle and the target will always remain the same, regardless of the magnification setting.
For example, the distance between two aim-points on the crosshair may equate to 4ins (10cm) on a target when it’s viewed at 4x magnification, and it will still be 4ins (10cm) when the scope is zoomed up to 12x magnification.