Optic Choices: First or Second Focal Plane?
BY Herschel Smith
2 years, 9 months ago
On an FFP the reticle expands or contracts in conjunction with the magnification, allowing the gradations of the reticle design, whether milliradian (mil), minute of angle (m.o.a.) or bullet drop compensating (BDC) to remain proportional. With the high range of magnification possible on today’s optics, it is a true luxury to crank the power to whatever is ideal for the level of support, the field of view desired and the precision of shot placement, then simply hold on the correct reticle gradation for the range and begin to press the trigger.
[ … ]
Most AR shooting, in whichever role—whether sporting, competition or duty/defense—is done within the “sweet spot” of the .223 Rem. trajectory where the shooter can simply hold on the intended target and get the hit. With the common 50-yd./200-yd. zero the bullet’s path is within the margin of error out to about 250 yds. This lets a shooter enjoy a consistent reticle image that remains the same, regardless of the magnification, and is still bold and visible at the low end.
However, if the shooter has to hold over for the occasional long shot with the magnification topped off at the maximum, the reticle holds are “true.” Six power is a good compromise for visibility at distance but is still low enough that many shooters can use maximum power from an unsteady support without getting motion sick from the image and, thus, prone to snatching the shot off.
I think this is a pretty good article, explaining what you’re giving up with each choice. For FFP scopes and high powered rifles, the reticle adjusts according to magnification. This lets the shooter more accurately judge holdovers with extreme distance and magnification.
But that reticle looks mighty small on low power. For SFP scopes, there is no need to go to high magnification to make accurate judgments of holdovers because the reticle is always the same size. But for extreme long range shooting (as long as you can get with an AR), that reticle won’t adjust with magnification.
Again, I think this is an informative article.
|
|
On July 21, 2021 at 10:39 pm, RHT447 said:
An excellent video on AR zero–
https://www.youtube.com/watch?v=DFbpjNh4DBA
Personally I prefer second focal plane. I am currently running a Burris RT-6 1-6x24mm on my AR.
On July 22, 2021 at 12:07 am, Georgiaboy61 said:
If the designer of the reticle has done his homework, a LPVO (second-focal plane) such as a Primary Arms GLx 1-6x ACSS or the Vortex Strike Eagle AR-BDC3 1-6x will be amount to two optics in one: De facto a reflex or red-dot sight at 1x close-range/CQB use, and a precision medium-range optic when set on high power (6x).
Even using a 30mm tube instead of a 1-inch, the eye-box on most 1-4x or 1-6x LPVOs is not going to be as-forgiving as a true reflex sight or red/green-dot type of design such as an EOTech or Aimpoint. Set at the lowest magnification, one still has to be properly within the eye box of the scope to obtain a clean sight picture.
For most users, much of the testing I’ve seen confirms that reflex & red/green-dot sights are still slightly faster than the best LPVOs when it comes to CQB-range snap-shooting. But the gap between them is getting narrower, as scope manufacturers learn how to make their products more user-friendly and versatile.
The slight loss of speed and size of eye-box is part of the trade-off involved in choosing an LPVO instead of something like an EOTech or an Aimpoint.
In return for a slight loss of speed and forgiveness in the eye-box, one gets a scope fully-variable and usable throughout its range, as well as the features of the reticle which can be used at different powers. Typically, some sort of inverted U or segmented circle, illuminated and designed to aid in acquiring a sight picture at low power, and features which are “true” only at maximum power, whether 4x, 6x or 8x. Such as range-finding, wind holds, bullet-drop compensation marks, and the like.
In other words, if you plan on doing predominantly up-close-and-personal types of shooting, you’ll probably be best-served by a dedicated close-range optical device, like an Aimpoint red-dot, 1x prism scope, or a holographic design like the EOTech. However, if you need versatility and flexibility, then a low-power variable optic is probably what you want.
LPVOs have come so far so fast that the U.S. military is now moving away from its time-tested fixed-power 3.5×35 Trijicon ACOGs, which have been in use for decades as standard equipment atop M4 carbines and M-16 rifles, in favor of low-power variable optics instead. Sig Sauer just won a big contract for supplying them to the U.S. Army, and they probably won’t be the last such transaction.
As a civilian, expect to pay more for quality FFP optics than their equivalent SFP designs. The gap is narrowing, but FFP still costs more. If cost is no object, then there is a simple litmus test one can do: If you need your reticle’s features to work when you want them to work, right then-and-there without fuss or remembering to check that your optic is set to 6x or whatever the maximum magnification is, then consider investing the extra dough in a FFP design. The reticle is true no matter what the power, and if you need more/less magnification to make the shot – you’ll be reminded of that right away when you look through the optic. If, on the other hand, you can remember to flip the magnification to maximum before using your reticle features, then a SFP design is probably for you.
Some reticle designs do not change significantly in appearance when the power is changed, even if installed in a FFP scope. If you have a simple duplex cross-hair reticle, it will look the same at any magnification, apart from the size and thickness of the cross-hairs.
If you do the majority of your shooting at a specific power, consider getting a fixed-power scope at whatever magnification suits your needs with your preferred reticle installed. Fixed-power scopes have fewer parts and therefore cost less and tend to be, all else considered, more robust than scopes with more internal sets of lenses.
On July 22, 2021 at 9:11 am, Russell G. said:
Just a slight warning. When you first move to a FFP it may (will) temporarily drive you nuts. Moreover, on some of the older (outstanding) scopes you can pick up on ebay et al., on the relative cheap, (from dimwad GenM/Xs selling their dead grandpa’s really cool stuff), the reticle will also move from the low power center position as you zoom…you’ll get used to it.
On July 22, 2021 at 11:14 am, will FORD said:
ON my AR’s I prefer a FFP @ 50′ site-in. On ALL both of my 7.62 x 51 I use SSP. I have no problems with hold over with either…Just my Opine. BTW LOTS of prac~tizin helps as in SERGEANT YORK “I ain’t to good a this here prac~tizin”. lov that one.
On July 22, 2021 at 2:58 pm, Geoff said:
I would love to have a FFP scope but most are beyond my financial means.
$100 SFP scopes works fine for me. I don’t shoot more than 100 yards anyway. No place near me with a longer range that’s free.
On July 22, 2021 at 4:14 pm, Swrichmond said:
It’s really about what it’s for and how good a rifleman you are. If you think 300 or 400 is a long shot, or if you shoot shit ammo through a shit barrel, don’t bother spending money on a FFP scope. Reticles have come a long way and holdover is easy now. Wind is still a factor of course.
On July 22, 2021 at 6:10 pm, sammy whittemore said:
im a broken down medically retired former working stiff. i do have some means , and with all the choices out there, i went with primary arms optics, after trying everything else. their ACSS reticles are the shiznit. i have a 5x prism optic, a few FFP lvpo optics, and a 4 of their DM 3 – 18x types as well. i’m not jumping out of planes or the like. i have been unable to hurt them so far. i will bet my life on them.
to be fair, i have 4 aimoint PROs, and 2 eo techs. all my PA optics are the platinum line. i shoot up to 1000 yds with the big ones, and am very impressed. im just gonna be in my hidey hole and wait for the shitbags to come to me. to me, the lvpo is the old chebby 350 of the optic world. YMMV.. see you bastards on the beach. sam.
On July 22, 2021 at 9:13 pm, 60gunuh said:
Huh, it seems the nra is occasionally good for something.