Dave Barham examines the new ED 4-16x50 SF scope from Discovery Optics

When the Ed plonked this scope on my desk and uttered the words "Fancy yourself as a scope reviewer, eh?" I immediately accepted the challenge. I hadn't had a vast deal of experience with high-end optics until recently, but having cast my eye down a fair few tubes over the past six months at recent shows and in the field, I believe I am more than confident enough to give a fair opinion on what makes a good scope.

What is ED Glass?

Let's cut straight to the point and talk about ED Glass shall we? ED stands for 'Extra-low Dispersion' and it refers to the composition and optical properties of the glass used for the lenses on these scopes.

ED glass is specially formulated and includes rare-earth compounds to reduce greatly any chromatic aberration - colours not all coming into focus at the same time in the same focal plane - compared to standard glass lenses. What this means is that it goes a long way to help eliminate colour fringes, which in turn gives much clearer, sharper images.

I won't bore you with the details, but fringes are a primary cause of soft focus, which is why cheaper SLR camera lenses tend to go ever so slightly fuzzy when you extend them to maximum range. It is especially common with cheaper lenses with over 200mm zoom ratings.

First impressions

As soon as I opened the box I noticed the gunmetal grey colouration of this scope. What a refreshing change not to have the bog-standard black! It's CNC machined from a single piece of T-6061 aircraft aluminium, which provides excellent rigidity as well as cutting down the weight. This scope has been put through some rigorous testing and Discovery claim that it has been tested to 1,500G shock - I have no reason to doubt them either, it feels really solid.

Upon removing the scope from the box for a closer look I noticed the reverse taper on the ocular and objective bells. They both taper slightly, getting larger toward the turrets, which adds to the aesthetics and overall feel of the scope.

The operation of the ocular bell magnification ring is super-smooth, yet a little stiff for the first-time use. That's only because it's new, and after a little 'warming up' it soon settles down and is easier to turn.

The scope is nitrogen purged and fully sealed. As a result it is said to be waterproof to 10 metres - great news if you happen to chuck your rifle into a lake! In all seriousness, though, the nitrogen process helps to prevent lens fog inside the scope, which can be a problem on cheaper scopes. Imagine a typical summer evening, when you get caught in torrential rain and your scope gets soaked, swiftly followed by bright sunshine and 25 degrees C drying everything out again - that's when lens fog can be a real problem.

Pull and twist turrets

Since I have been getting more involved in scope cosmetics and functionality in recent months, I have come to the conclusion that turret covers are a pain in the backside. They never used to bother me as a kid, but having used plenty of scopes with designs that have done away with these covers I am definitely a convert.

This scope is no exception - not a turret cover in sight! Instead, to protect the turrets from being accidentally moved during transportation, this scope features a pull and twist system. You basically have to pull the turret out before you can adjust the windage or elevation. Once you're done, you simply push the turret back down into place where it locks itself, with no chance of it moving again until it is physically pulled up. It's a great system, and a huge plus point for me.

The adjustments themselves are positive clicks, too, so you know exactly where you are with them - there's no 'did that click once or twice?' with these turrets.

Sidewheel focus

Inside the 'box of never-ending goodies' I also found a large side wheel, which can be attached to the scope in a matter of seconds.

On the left-hand side of the turret set-up there is a simple parallax adjustment knob, which as you would expect on a scope of this quality, running from 10 yards to infinity.

Unscrewing said 'Discovery' knob reveals a four-way recess into which the two-way male connectors on the underside of the supplied sidewheel slot. I'm not sure why there are four recesses and only two male pins, but that doesn't affect the system in any way. Once you have pushed the wheel into place you simply screw the 'Discovery' knob back on and it's all systems go.

The action is smooth and precise, and it all feels very solid.

Interesting reticle

Although Discovery classes this as a mil dot, it is in fact a whole lot more than that as far as the reticle is concerned. You'll see from the diagram that the reticle does indeed have mil dots, well, lines really, but you will also notice that each 'mil dot' is broken down further into segmented half and quarter mil increments up to 5mm on both the horizontal and vertical planes, with a further breakdown into 1/8 mil from 5 to 8 on the horizontal.

You'll also notice that this reticle has a windage tree below the main horizontal crosshair. Although used mainly for long-range firearms shooting, if you get to learn your scope and how to use it in windy conditions, this can be a vital tool for us airgunners too.

Mega mounts

Before I jump to my conclusion, I have to mention the mounts supplied with this review scope. What a great piece of kit! Discovery supplied their two-piece mounts, which rather than having Allen screws to attach the base of the mounts to the rail, have large nuts instead. I always carry a small ratchet socket set with me in my toolbag, so attaching the mounts was really quick and very precise. Top marks again to Discovery for these.


I really like this scope. It's aesthetically pleasing, and more importantly, extremely good quality and a doddle to use. I love the fact that the mount is so easy to adjust and tighten, too. That makes strip down and cleaning after a soaking far easier, and it's something you can do immediately, in the confines of your vehicle, rather than waiting until you get home.

If you fancy dropping something a bit different atop your favourite rifle, then I suggest you take a good look at this offering from Discovery Optics.

Key features:

- ED Japanese FCD100 HOYA glass lenses provide an extremely low chromatic dispersion, bright and sharp image.

- One piece T-6061 aircraft aluminium, CNC machined and hard anodised scope tube, accurate and solid construction. Tested to 1500 G shock.

- 4 or 5x times optical design provide a long-range power for long-range shooting and hunting.

- Objective Fixed Technology makes the ED line more reliable and recoil proof for large calibre and lifetime use.

- Positive Pressure Nitrogen Filling gives 10 metres waterproof and better fogproof performance.

- Side focus from 10 yards and comes with a side wheel for easier use.

- Comes supplied with protective rubber lens covers.


Chassis: 30mm

Optical system: 4-16x

Objective: 50mm

Reticle: Mil dot

Ilumination: N/A

Focus/parallax: Side focus 9m/10yds to infinity

Field of view: 6.6 - 1.32m @100m

Eye relief: 85-100mm

Length: 312mm

Weight: 625g

Website: disoveryoptics.co.uk

RRP: £399