Trijicon's AccuPoint

September 23, 2010 By J. Guthrie

It's All About Light

By J. Guthrie

Light. The optical systems are designed to transmit it, the scope's extra parts are placed around it, fiber optics move it from place to place, and tritium gas and phosphors produce it. So when you look through a Trijicon AccuPoint scope, know that light was the primary consideration of the designers.

While most shooters are aware of Trijicon's Advanced Combat Optical Gunsight, or ACOG, which has been a tremendous enhancement on the battle rifles of U.S. Marines since 2004, many are unaware that Trijicon has been producing a line of riflescopes — the AccuPoint line — specifically for hunters since 1998. The five different available AccuPoint models work well on law enforcement and home-defense rifles and shotguns, but Trijicon founder Glyn Bindon was an avid hunter and knew the shooting concept he pioneered was perfect for a wide range of civilian hunting and shooting applications.

An illuminated reticle is an important feature in many hunting situations. Most scope companies have models with illumination, but the catch is an additional hundred bucks or more on the price tag and a battery that can die at the most inopportune times. AccuPoint scopes get around this by the skillful application of technology. The primary way engineers deliver light to a reticle during daylight hours is to redirect ambient light into the scope tube by way of a fiber optic.

Tom Maciak is Trijicon's technology development and engineering supervisor and a mechanical engineer by trade. He and a team of scientists, machinists, and engineers spend a lot of time applying fiber-optic technology to riflescopes. While it may seem easy to just work a fiber optic into a scope, Maciak explained that they are, by nature, very fragile.

"The colored fibers you see around the ocular are collecting fibers," Maciak said. "Outside light is essentially going into a light pipe — it can get in, but it can't get out. The fiber is composed of a core and cladding, and the outside cladding's chemical composition keeps the light in, bounces it around, while the core transmits light along its length."

These amazing properties have been applied to an astounding array of technologies, but before Bindon, never to gun sights. The core is soft, but the cladding is much harder, brittle even. Trijicon has fiber optics built to its specs, but the basic rules still apply. Fibers travel through the scope tube along sweeping paths that avoid hard angles and are locked in place with adhesives or channels cut into the scope body. This insulates the fiber from the recoil shock they were never designed to withstand in the first place.

"We have to be very careful when handling the fiber to avoid cracks in the cladding, which would allow light to escape and create a less efficient system, dimming the reticle," Maciak said. "Fiber optics weren't designed to do this, and you can do a lot to screw them up. That's the genius of Glyn Bindon, who took this and made it work."

In addition to being fragile, the fiber-optic strands are tiny. Generally measured in microns, the AccuPoint's little reticle light pipes are only about the width of a human hair. The length of fiber optic controls the amount of light transmitted and, in turn, controls the light output at the reticle. Shooters can control reticle intensity by rotating the ocular bell, which acts as a sunshade, covering the fiber-optic strands. But the system is mostly self-regulating.

"A lot of engineering work went into figuring out how much fiber optic is enough to illuminate the reticle, and the final length is proprietary information," Maciak said. "We started with an inch of fiber and looked at using more than a meter — there was a lot of trial and error — and found there is a point of diminishing returns. Generally, there is enough light to illuminate the reticle to match the available ambient light plus a little more."

In the AccuPoint models with a BAC reticle, the triangular aiming point starts out round. Turning the round fiber into a triangle is another patented Trijicon innovation. Once the desired shape is created and the perfect length found, the fiber's end is cut at an angle and polished so that shooters can see the light transmitted by the fiber-optic collecting coils. Amazingly enough, the post reticle is simply an upturned, unsupported fiber sitting in the tube. While there appears to be a supporting wire, it is actually a clear fiber that appears black because of the constant backlighting. The fiber, though delicate, has very little mass and is unaffected by recoil.

Trijicon recently added traditional crosshairs to the AccuPoint line, including duplex, mil-dot, and German No. 4 reticle styles. At their center point, the wire reticles have a small, illuminated dot just like the original post reticle. The fiber optic is affixed to the wire with epoxy.

Each day the sun sets and darkness creeps across the land, and the AccuPoint's fiber optics are left, literally, in the dark. The majority of scope makers simply add a small LED unit to feed light to a fiber optic or etched reticle. That requires additional circuitry, a rheostat to control light output, and a battery. Trijicon went another direction and powers the reticle with a radioactive isotope of hydrogen called tritium, or 3H.

The fiber's length is critical for managing light. The system pipes in just enough

light to be slightly brighter than ambient light conditions.

"The glass lamp is coated with a phosphorus material and the 3H excites that phosphorus, causing it to give off light," Maciak said. "The scope lamps are larger than those found on our night sights. The 3H's half-life is 12 to 15 years, meaning that the lamp will produce half as much light after that period of time. But it is possible to replace the lamp if need be."

There are stringent, exhaustive testing requirements by the Nuclear Regulatory Commission, and the 3H cannot be accessed without tools. The scope's fiber optics and 3H lamp are bucked together so the reticle is powered day or night. The system's only disadvantage is there is only one 3H setting — it is what it is. Scopes with rheos

tats and LEDs can dial the light up or down depending on conditions and can be made to work with night vision equipment.

With all the considerations given to fiber optics and the addition of tritium lamps, it is easy to see why the ACOG has an unusual shape. Maciak said engineers first designed the optical system, added the extra parts, and then "shrink wrapped" the unit in an aluminum housing. Other than the slightly oversized ocular bell that holds the fiber-optic coils, AccuPoint scopes look ordinary in every way and still fit full-sized lens elements in their 1-inch and 30mm tubes.

In the Bindon Aiming Concept (BAC), the human eye is drawn to the magnified portion of its field of view and focuses on the reticle. When a target moves, the eye reverts to the unmagnified field of view seen by the other eye. This allows for precise aiming while maintaining a full field of view.

"We start with the optical system and design around the light rays so they are not clipped by any of the internal components," Maciak said. "We know where to put things and not put them."

Depending on the model, AccuPoints have 90 to 95 percent light transmission. Plenty of companies claim exceptional performance levels, but Trijicon engineers prove it with spectroradiometers. Maciak said the company uses the best possible, fully multicoated glass throughout its product lines, military and civilian. Lenses are ground and coatings are applied to spec via vapor deposition and then qualified before being used in an optic. Internal adjustment mechanisms get the same attention.

"Most of the internal components are aluminum, but the relay-cam components are brass or bronze because of the metals' natural lubricity," Maciak said. "The parts are held to half-thousandth-inch tolerances, allowing them to move smoothly but maintain zero by not moving off axis."

When paired with a Savage Long Range Precision Varminter, the 5-20X had no problem shooting the square in the author's tests. Precision machining, quality components, and exceptional quality control are standard features of AccuPoint scopes.

AccuPoint tubes are machined from 6061 T6 aluminum bar stock and are hard-coat anodized. Tubes are sealed with o-rings and nitrogen purged to prevent internal fogging. The erector tube is held in place with a ball joint at the rear and a steel spring up front that sits opposite the windage and elevation adjustments, a pretty standard arrangement. Before shipping, every scope is run through a battery of function checks — every scope.

"All of our optics are put through extensive tests," Maciak said. "They are nitrogen purged and leak tested with a mass flow meter that will sense any loss of pressure. The scope is put in a fixture to adjust the parallax, and an experienced technician runs a mechanical check on the adjusters and adjustments at the same time."

There are just five models in the AccuPoint line, but they cover the bases pretty well and are at home in both the hunting and tactical worlds. Probably the two most versatile scopes are the 1-4X 24mm and the 1.25-4X 24mm. Both can be had with the original BAC triangle or a German No. 4 reticle, and the only difference between the two is tube size, with the 1-4X 24mm sporting a larger, 30mm tube.

These two models, because of their wide fields of view, are great for dangerous-game rifles. While my dangerous-game hunting ex-perience is pretty much nil, I asked for fellow InterMedia Outdoors contributor Craig Boddington's thoughts. He needs no introduction. "I am not sure there has ever been a better dangerous-game scope," Boddington said in an e-mail reply. Simple enough. Muzzleloader and slug hunters would do well to take a close look at these scopes as well.

The 4X setting offers plenty enough magnification for long shots, and the lowest setting, with practice, is faster and more accurate than iron sights since the reticle and target appear on the same focal plane. The illuminated reticle is great for placing shots on dark game hiding in the shadows. For many of the same reasons, tactical rifles — carbines in particular — are a great match for the two scopes. Dialed up, hits at several hundred yards are easy, and dialed down, the optic and its illuminated reticle perform like high-speed reflex or holographic CQB optics.

Most hunters will probably lean towards the 2.5-10X 56mm or 3-9X 40mm variables, depending on how much glass they want sitting on top of their rifles. Both scopes can be had with standard, mil-dot, or BAC reticles, but the 3-9X 40mm's smaller 1-inch tube and objective save around 7 ounces and shave $150 off the price tag. Just last year I used a 3-9X 40mm with a mil-dot reticle on a South Texas hog hunt. Mounted on a Remington Model 700 in .30-06, the combination proved to be potent. Late into the evening, the small illuminated center dot was invaluable for placing bullets on black, mud-covered pigs. The dot sits completely inside the reticle and is very precise, even at long ranges.

Sitting atop the magnification pile is the 5-20X 50mm. Meant for long-range precision and varmint rifles, the scope is equipped with target turrets with quarter-minute adjustments and can be had with standard, mil-dot, and BAC reticles. At 20X, it is clear that Maciak's claims of high-end optical quality are true. Helped by a side-focus knob, at its highest magnification, the 5-20X 50mm presents a bright, crisp image from edge to edge.

In terms of price, the AccuPoints are an exceptional value. The attention to the optical system's design elevates their level of light transmission and puts the scopes' performance on par with more expensive brands.

As the saying goes, "often imitated, never duplicated." Other manufacturers have applied the same materials and technologies to their optics, but no one does it quite like Trijicon. The innovative way in which its reticles are illuminated almost outshines the exceptional optical quality of the AccuPoint line.

Specifications
Model:	1-4X24mm AccuPoint	1.25-4X24mm AccuPoint	2.5-10X56mm AccuPoint	3.9X40mm AccuPoint	5-20X50mm AccuPoint
Magnification:	1-4X	1-4X	2.5-10X	3-9X	5-20X
Length:	10.3 in	10.5 in	13.8 in	12.4 in	13.6 in. (16.6 in. with sunshade)
Objective Size:	24mm	24mm	56mm	40mm	50mm
Weight:	14.4 oz.	11.7 oz.	20.7 oz.	13.4 oz.	26.9 oz. (29.4 oz. with sunshade)
Illumination Source:	Fiber optics, tritium	Fiber optics, tritium	Fiber optics, tritium	Fiber optics, tritium	Fiber optics, tritium
Reticle Patterns	BAC triangle, German	BAC triangle, German	BAC triangle, standard crosshair	BAC triangle, standard crosshair	BAC triangle, standard crosshair
	No.4 reticle with dot	No.4 reticle with dot	with dot, mil-dot crosshair with dot	with dot, mil-dot crosshair with dot	with dot, mil-dot crosshair with dot
Reticle Colors	Amber(BAC triangle, No.4)	Amber(BAC triangle, No.4)	Amber	Amber	Amber
	Green(BAC triangle, NO. 4)	Green(BAC triangle, NO. 4)	Green	Green	Green
	red(BAC triangle)	red(BAC triangle)	red(BAC triangle)	red(BAC triangle)	red(BAC triangle)
Eye Relief:	3.2 in.	3.4-4.8 in.	2.8-4.1 in.	3.2-4.6 in.	3.8-4.1 in.
Exit Pupil:	17.5-5.1mm	16.9-6mm	16.3-5.6mm	13.4-4.4mm	10-2.5mm
Field of View @ 100 Yards:	97.5-24.2ft	61.6-20.5ft	37.6-10.1ft	33.8-11.3ft	97.5-24.2ft
Adjustments:	1/4 in. per click @ 100 yds.	1/4 in. per click @ 100 yds.	1/4 in. per click @ 100 yds.	1/4 in. per click @ 100 yds.	1/4 in. per click @ 100 yds.
Tube Size:	30mm	1 in.	30mm	1in.	30mm
Housing Material:	6061 T6 aluminum	6061 T6 aluminum	6061 T6 aluminum	6061 T6 aluminum	6061 T6 aluminum
Finish:	Type III, Class 2 dull and nonreflective	Type III, Class 2 dull and nonreflective	Type III, Class 2 dull and nonreflective	Type III, Class 2 dull and nonreflective	Type III, Class 2 dull and nonreflective