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Optics Riflescopes

Leupold Mk8 3.5-25x56mm

by Tom Beckstrand   |  June 23rd, 2017 0

LeupoldMark83.5-25x56mm
Shopping for a set of features can turn into a prohibitively expensive affair if we name everything we want without considering what we need. However, when the checkbook can support a lengthy list of wants and needs, the Leupold Mark 8 3.5-25x56mm is the king of the optics jungle.

No scope packs more features into a single optic than this Mark 8. Everything from the night-vision friendly magnification range and illumination system to the locking turrets with zero-stop, revolution indicator and tool-less zero make this the most feature-rich scope produced to date. Optical quality is also exceptional, and there’s a long list of reasons why.

PRIORITIES
I’ve had the opportunity to talk to the optical engineers at Leupold on a couple of occasions and always came away impressed with their understanding and devotion to the subject. Optical engineers will always tell you that there is more than one way to build a scope, so it’s important to prioritize.

Leupold is tight-lipped about why they do what they do, but a former member of USASOC’s combat development team once mentioned to me that he helped write some of the requirements for the Mark 8 scope, and that Leupold was very focused on producing the scope exactly how those specifications were written, painful though it might be. The Special Operations crowd has some unique needs and a long list of priorities, both of which are pretty easy to identify once we start examining the 3.5-25X.

The pinch-lock turret ensures that only deliberate effort can turn the dial.

The pinch-lock turret ensures that only deliberate effort can turn the dial.

The easiest place to start listing features starts with the turret system. The Mark 8 has a locking turret that requires the shooter to pinch the top of the turret together prior to making an adjustment. The system was undoubtedly complicated to make, but is simple to operate. Pinch, turn, release. Once released, everything locks up tight.

I learned a hard lesson at a shooting competition when I moved from one firing position to another with an unlocked turret. I banged my rifle into the side of an opening and didn’t think anything about it because I was focused on hitting my target. I missed a couple of shots and then time ran out. When I looked at my turret, I realized it had spun almost an entire mil from what I dialed. When my turret impacted the opening, the wall adjusted my turret for me.

Leupold’s locking system would have prevented this problem because it takes opposing pressure to unlock and turn their turret. You have to pinch before you turn. Beating on one side won’t do it. It sounds like a small matter, but the Mark 8’s locking system is the best I’ve seen. There will be no impact-adjusted turrets with the Mark 8.

The turret sophistication continues with a tool-less zeroing system. There are two opposing pins that hold a collar at the base of the turret in place. Depressing both pins and holding them down allows the collar to be pulled up and off the turret, or up and spun around to zero the turret. The collar can be pulled off and any custom ballistic drop collar can be put in its place. It’d even be possible to have a bag full of collars for each cartridge and common environmental conditions.

The turret has a simple zero-stop that is easy to adjust. The shooter has to loosen a small hex-head screw that sits just above the collar on the turret. Once this screw is loose, the turret spins around until it hits a hard internal stop. Tighten the screw back down and the zero-stop is set.

SCOPE FORENSICS
The first thing about the Mark 8’s dimensions that screams for attention is the 35mm maintube. That’s a non-standard tube size, which means that mounting options will be limited and aftermarket support will

The ring around the base of the turret can be removed or re-zeroed by depressing the two retaining pins, and then lifting and rotating the ring to the desired position.

The ring around the base of the turret can be removed or
re-zeroed by depressing the two retaining pins, and then lifting and rotating the ring to the desired position.

be minimal. Why would Leupold do something like that?

Once we start examining the fine print on Leupold’s brutally honest specification sheet, we find the answer. First, some important background information. Every scope is different, but a general rule of thumb for scopes with a maximum magnification of 25X or so is that every .1-mil of elevation or windage adjustment requires .0008-inch movement of the erector assembly (depending on the scope’s focal length).

Scopes with large amounts of erector travel generally have smaller erector tubes and smaller lenses in them. A maintube only has so much space inside, and it can be filled with glass or be left empty so the erector can move around. The larger the erector assembly, the larger the lenses that can be put in it. Large lenses give a larger field of view.

The Mark 8 has a larger than normal maintube, an excellent field of view and is on the small side of average for amounts of elevation and windage adjustment. While the numbers all look good, they still don’t explain the need for a larger maintube. That extra millimeter of maintube is responsible for about 5 mils of erector travel but it doesn’t have a ton of travel in general. Something is taking up the real estate inside the maintube.

That something is a sophisticated illumination system. Leupold is the only optics company that offers night-vision compatible illuminated Horus reticles. I can’t imagine how complicated it must have been to work out the illumination system for this scope. Normally, etched reticles have a reflective substance filled in the reticle and then red LED light gets projected across the whole lens. The reflective substance bounces the red light back to the shooter’s eye and the parts of the reticle that have the reflective substance appear to illuminate.

That type of lighting arrangement works OK for first focal plane reticles and not at all for scopes that have to be night-vision capable. The problem is managing the LED light that gets projected onto the lens containing the reticle. The above technique sends a lot of light at the lens and only a small portion of it LeupoldMark83.5-25x56mm_4hits reflective material and bounces back to the shooter’s eye. The rest of it winds up impacting the inside of the maintube body where the lens butts up against it and is easily seen as the bright-red ring that sometimes appears around the edge of the field of view.

First focal plane scopes are even more difficult to illuminate because the lens housing the reticle sits right under the turrets. That’s some prime real estate, so cramming an illumination system in a first focal scope is an unpleasant engineering experience.

If illuminating a first focal reticle is tough, keeping it night-vision capable is a nightmare. Night-vision equipment doesn’t take kindly to red LED light running around willy-nilly inside a scope. That bright-red ring mentioned above will wash out an IR-amplified image in a heartbeat, so the “easy” way of illuminating a first focal reticle is out.

To top it off, the Mark 8’s illuminated reticles have multiple points that are lit up. The system that Leupold developed for this scope required very controlled portions of light routed through to the chosen illumination points and nowhere else inside the entire scope or else it wouldn’t be compatible with night-vision equipment.

#BLM – BIG LENSES MATTER
A senior employee of Leupold once told me that a single lens in the Mark 8 scope costs them several hundred dollars. That’s a ton of cash for the manufacturer to produce one lens. It’s also a big reason why the optical quality of the Mark 8 is so good.

A quick glance at the 3.5-25X tells us that it has a high probability of excellent optical quality just from its size and length. Long is a good thing when it comes to image quality in scopes. Long scopes have long focal lengths, which helps keep all spectrums of light in the same focal plane as they pass from one lens to the next. Combine the length of the Mark 8 with the high-quality lenses inside, and we’ve got the recipe for excellent image quality.

Image quality can be such a subjective term, but the Mark 8 is a joy to look through because it offers great resolution and contrast, a difficult combination to achieve. The edges of objects in the field of view are sharp with no detectable aberration, which is important when looking through a scope for hours at a time. The depth of field is also excellent. This is an often overlooked and misunderstood aspect of scope performance.

I’ve seen people complain when, past a few hundred yards, the parallax knob wasn’t needed to remove parallax from the scope because there was none. The depth of field was so great that objects remained in focus for several hundred yards at a time with no detectable parallax. I wanted to scream that an optical engineer worked very hard to make the scope perform like that.

Many know that parallax occurs when the field-of-view image isn’t in the same focal plane as the reticle. It takes a ton of optical horsepower and a lot of cash to take objects from significantly different distances and focus them all into the same focal plane. This is called “depth of field.”

The advantage to the sniper whose scope has great depth of field is that there’s no need to adjust parallax when shooting a multiple target engagement. Having one less turret to touch whilst spreading the good news means more shooting and less scope adjusting. A great depth of field is hard to come by, but it’s worth the money when it comes time to shoot for real. Depth of field is also rarely discussed, so good information is hard to find.

The Mark 8 has an exceptional depth of field, especially for a scope that has such a high-power zoom range and a large objective lens. Leupold achieved great depth of field by making the scope long and using several very high quality lenses (that also give it fantastic image
quality).

LeupoldMark83.5-25x56mm_5

No scope currently on the market has a list of features as comprehensive as the Mark 8.

The photographers in the room should think of depth of field in terms of f-stop. Numerically high f-stops give great depth of field but also have small entrance pupils or apertures. F-stop is determined by dividing focal length by entrance pupil. Think of the entrance pupil as the objective lens: It’s fixed.

With the size of the objective lens remaining fixed, depth of field will be determined by focal length. Physical length of the scope is a contributing factor, but so are the number of lenses and the quality of the lenses in a scope. The more lenses in a scope, the more focal length can be “lengthened.” Lots of focal length means large f-stop numbers and that gives great depth of field.

Two fairly accurate ways for a potential consumer to determine if a scope will have good depth of field are to look at how long it is and then take a peek through it to assess image quality. (Never assess image quality with indoor lighting.) Scopes that struggle with chromatic aberration will likely never have great depth of field. Chromatic aberration indicates poor focal length management, whether it comes from weak coatings or low-quality lenses. While chromatic aberration and short depth of field are different symptoms, the sickness is the same: poor focal length management. Short depth of field does not guarantee chromatic aberration, but chromatic aberration usually indicates weak depth of field.

Leupold’s Mark 8 3.5-25x56mm scope has a ton of unique features that wound up in the same place because some Special Operations folks generated a long list of esoteric requirements, and Leupold wanted to check every box on the list. Everything from the turret design to the illumination system to the fantastic image quality and great depth of field speaks to a discerning customer with a healthy budget and high standards. While not every sniper needs all the features, there are a handful that do.

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