Scope Clarity: It’s Not The Glass

I get a bit irked when folks talk about the “good glass” in scopes. It’s not the glass…it’s the coatings! After touring several scope manufacturing plants and talking with several optical engineers, I’ve learned that glass is glass. They don’t buy “cheap,” “better” and “best” glass to put in these instruments. They WILL specify a certain type of glass with varying degrees of refractive index to deliver specific performance, but quality of Brand X’s glass isn’t any better than Brand Y’s or Z’s glass of the same type.

The coatings might be.

Coatings are not an afterthought. They make the difference between bright and dim. Once a scope’s objective lens has been ground and polished, maximum sharpness (resolution) has been achieved. The rest of the lenses in the scope can only degrade this. They are designed to reverse and erect the upside down image the objective lens produces. A parallax adjustment lens may be added for precise focus. Eyepiece lenses are used to magnify the initial image. That’s about it. Grind, polish and mount all these lenses properly and you maintain top-end resolution and sharpness.

As for brightness (more accurately, light transmission), the more lenses, the worse it gets. This is due to reflection. The reason you see a dim image of yourself in a window is because some of the light reflects off the window. In a scope, about 4 percent of the light striking each raw glass surface is lost to reflection. Another 4 percent is lost when the light leaves that lens. There can be eight- to 10 air/glass surfaces in a scope, costing you up to 80 percent of the light!

Anti-reflection coatings reduce this loss to as little as 0.02 percent per air/glass surface. It takes multiple layers of these to get to that level. This is a big difference between $150 and $1,500 scopes.

The next time you’re admiring a sharp, bright image through a scope, impress your friends (and probably the salesman) by exclaiming: “Wow, the glass in this scope is precisely ground and wears some killer anti-reflection coatings.”

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8 Responses to “Scope Clarity: It’s Not The Glass”

  1. Avatar

    john e. thomas jr

    Thank You for Ron Spider’s detailed info on scopes

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    I think sometimes we pick at the nitty gritty too much! When I say Great Glass, I am referring to the scope in its entirety, not just the “glass”. I did enjoy the facts about the amounts of reflection and such. I would have loved to go on a tour of a great scope manufacturing facility. And we all know, a scope can make or break the shooting experience. It doesn’t bother me if you say “good glass” though, because I understand what you are saying…. “That scope is awesome”…

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    Eugene Schwickerath

    About time an author states what really happens in a scope. Too many of the uninformed do not know what is really occurring in a good scope!! Thank You !!

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    Ed in Tx

    Good article. Lens is something I have wondered about.
    I have a ?? though. I have laped the rings for my new leatherman 4×16-44mm scope from SG. Mounted using levels on a pictiny rail. I have used a cartrige laser to dial it in, on a 308 savage axis. I have checked and rechecked this.
    When I go to the range. Im 1″ below bullseye(not a problem), but Im 12″ to the left,(sandbaged). Takes allmost all the windage to line it. Whats wrong lenes’, bent barrell? I have tried various ammo, Same results.
    Im new to hunting rifles. Thanks for some, any info..

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      Sir, it looks like you did things properly. While it’s possible that the pic rail or rings could be out of spec, the scope is probably bad. Return it to SG; install it’s replacement, and you will be good to go. If you can afford a better quality scope, do so.

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        Ed in Tx

        Thanks Gary, I have thought of that. I need to find packing slip. I made a mistake this is a leatherwood hi-lux scope, not leatherman. Not a top of the line, but what we used in ‘Nam. I think I paid SG about $100 on sale, 2yrs ago. I would like beter but at 68yrs old on fixed income. That is why I bought the savage axis on sale, price. Cant compare the scope to open an site, as it has none.
        If SG will replace the scope, maybe a replacement will fix it. This is my first hunting rifle. I thought I would try hunting at least once in my life. This has been my hold up.

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    Dave Rossi

    You the man, Ron. You the man.

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    Great article, I actually learned something even though I just read it on December 12, 2019!! Thanks for the info!!!