Vortex Optics VIPER PST 2.5-10X44 RIFLESCOPE - Manual (Page 3)

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RIFLESCOPE
r
eTicle
o
pTionS
The Focal Plane
All riflescope reticles can be termed either first focal plane (FFP) or
second focal plane (SFP), depending upon their internal location within
the riflescope. Many Viper PSTs are available in both reticle styles.
First Focal Plane Reticles
First focal plane (FFP) reticles are located near the windage and
elevation turrets in front of the image-erecting and magnifying lenses.
This style of reticle will visually grow and shrink as you change the
magnification. The main advantage of an FFP reticle is that the reticle
subtensions used for ranging, holdovers, and wind drift corrections
are consistent at all magnifications. The reticle is heavier at higher
magnifications and finer at lower magnifications.
Second Focal Plane Reticles
Second focal plane (SFP) reticles are located near the scope’s eyepiece
behind the image erecting and magnifying lenses. This style of reticle
does not visually change in size when you change the magnification.
The advantage of an SFP reticle is that it always maintains the same
appearance. Listed reticle subtensions used for estimating range,
holdover, and wind drift correction are only accurate at one particular
magnification.
If the adjustment is in MOAs,
the turret will display
“1 Click = ¼ MOA”. If the adjustment is in mrads,
the turret will display
“1 click = .1 mrad”.
The Subtension Scale: MOA or MRAD
Depending on which version you have purchased, your Viper PST
riflescope will feature adjustments and reticles scaled in MOAs or mrads.
If you are unsure of which scale is used, reference the top of the adjustment
turret.
Both minute-of-angle (MOA) and milliradian (mrad) unit of arc scales are
effective when ranging or adjusting riflescope for bullet trajectory.
MOA Adjustments
MOA unit of arc measurements are based on degrees and minutes. There
are 360 degrees in a circle and 60 minutes in a degree for a total of 21,600
minutes (MOA) in a circle. A minute of angle will subtend 1.05 inches at
a distance of 100 yards. Viper PST riflescopes with MOA adjustments use
1/4-minute clicks which subtend .26 inches at 100 yards, .52 inches at 200
yards, .78 inches at 300 yards, etc.
MRAD Adjustments
Mrad unit of arc measurements are based on the radian. A radian is the
angle subtended at the center of a circle by an arc that is equal in length
to the radius of the circle. There are 6.283 radians in all circles and 1000
milliradian in a radian for a total of 6283 milliradians (mrads) in a circle.
An mrad will subtend 3.6 inches at a distance of 100 yards. Viper PST
riflescopes with mrad adjustments use .1 mrad clicks which subtend .36
inches at 100 yards, .72 inches at 200 yards (2 cm at 200 meters), 1.08
inches at 300 yards (3 cm at 300 meters), etc.