View Full Version : Requesting basic scope information...

10-09-2007, 10:26 PM
I am trying to learn more about rifle scopes. Are there any links out there that can explain what the numbers mean, such as 3x9x40mm? What is an objective lens? The different things to look for when buying a scope, how to tell which mounts and rings match your scope or rifle, why are some so expensive and others so cheap...etc.
Basically, I'm looking for a website that will explain to me scopes 101.


10-09-2007, 11:11 PM
There's likely some good info on webpages at www.riflescopes.com (part of SWFA).

The number "3-9x40" means scope offers magnification from 3X up to 9X, and that there's a 40mm objective lens (the one facing the target). Most regular adjustable scopes cover a triple or quadruple magnification adjustment range; you'll hardly ever see, say, anything like 2X to 20X adjustment except for pricey specialty scopes.

Some scopes have 1" tubes while others have wider 30mm tubes. Some folks say the 30mms are better/brighter but there are plenty of fine 1" tube scopes.

Some scopes have finger-adjustable windage & elevation knobs (tactical/varmint/target/sniper), while others (hunting and quite a few target apps) have knobs under covers that may require a dime to adjust screws. For many folks the latter is best.

Shorter range scopes may have fixed "parallax" (essentially focus) adjustment, while others have adjustable parallax - and more expensive ones often adjust this from the side instead of the front bell of the scope.

Fixed-power (nonadjustable magnification) scopes are fairly common, esp in lower magnification ranges. 4X is fairly common one. The higher the magnification the smaller the field of view (i.e., how much area out front you can see thru the scope) - and with higher magnifications time taken to find something thru the scope ("sighting time") can take an uncomfortably longer time for quick-response shots. (This is one reason some optic sights use 1X (no magnification) and just use a red dot - for fast on-target applications where precise long distance shooting isn't required.)

Scopes can be graded in two key areas: optic quality and mechanism quality. Really great optics don't do you much good if the reticle (the 'cross hairs') can't stay zeroed (on target) due to shock/vibration, or change unpredictably due to adjustment - however, scopes known for good or very good optics usually don't suffer this problem. They also are sturdy in the right places, purged with nitrogen, sealed well, have antifog/antiglare coatings, etc. You get what you pay for.

Cheap scopes (i.e, Red China) sometimes appear to be nice & bright on quick perusal. But when onditions change a bit - lower light, glare, etc - and then substanard performace really reveals itself. There's chromatic distortion at lens edges, scope can't focus well at extended ranges, and more importantly a reliable zero can be hard to maintain. Cheap mechanisms cause movement of scope zero (thus point of impact) since adjusting windage (left-right adjustment) interferes with/changes elevation setting (up/down adjustment) and vice versa. Some cheap scopes even change zero when magnification changes!

Poor optic planning/design can also result in a cheap scope having poor (too close) eye relief - that is, not a proper distance from eye to rear lens - or widely varying eye relief with change in magnification. You really don't want short eye relief on a magnum rifle :)

Some folks say to pay as much for the scope as for the rifle - a fancy rifle doesn't do much good if you can't see the target or maintain zero. However, there are quite good scopes at reasonable prices - newbies can do very very well with Burris or Nikon scopes. In fact the Burris 3x9-40 Fullfield II scope runs around $190 and is a very good scope and one of the best deals for a starting scope out there. Other folks here speak well of Nikon Buckmasters, and Leupold VXII scopes, and Bushnell has a few higher-end scopes in the Elite line that are pretty good. You can find a good scope for under $300 and often in $250 range. Higher magnifications beyond 3-9x cost more. Bigger front bells (50mm) that let in more light (but are heavier) cost more and for many folks are unnecessary. While all these scopes are quite good as you pay more you do get improved optic performance, better reticles, features like illuminated reticles, etc.

I and many others here will tell you to stay away from brands like Tasco ("Trashco"), BSA, Simmons, NcStar, Leapers.
Some of these cheap Red Chinese scopes have western- or European sounding names (Mueller) or Japanese-sounding names ("Nikko-Sterling"). Newbies finding a really good deal on a Leupold tactical scope should be cautious too since their are cheap (and illegal) Red Chinese copies floating around. If a deal is too good to be true, it probably is.

Scope mounts and rings are another area where it pays not to save money. Look at Leupold or Burris ring sets and mounts (military stuff for AR15 and Picatinny rail rifles is a whole 'nuther thing). Cheap/unsteady mounts can drift and even a thousandth of an inch imperceptible 'slop' can cause your bullet impact to move on the target (esp after your scope has been jarred around inside a rifle case while travelling on an airliner). Decent rings and bases can easily run $60 or more depending on size and type of mount on rifle - and some ring sets can go for hundreds, though this is likely outside the 'scope' of your needs (pardon my pun).

People can ruin scopes by mounting them incorrectly (under tension due to ring misalignment). If you don't know what you're doing, pay a smith to install one and ensure ring alignment - and get it boresighted (i.e, fairly close to zero so you're shooting "on the paper" at 50yds and can fine tune). Sometimes the combination of production variabilities in the mount, scope and rifle can stack up and the scope's natural optical center is way off from target zero. Rather than adjust the scope to its extreme settings to get it zeroed it makes more sense to 'shim' the base/rings with thin layer(s) of shimstock metal so as to keep scope's optical center fairly close to real-world zero.

10-10-2007, 8:25 AM
hey sig22018 (http://www.calguns.net/calgunforum/member.php?u=10336) ur in the same boat i am. my OLL has been sitting for almost a year since i can't seem to find time to understand scopes, and when i do, it's like another language to me. so i said screw it.. i bought an eotech 512 over the weekend, but i still need to learn more since i'd like iron sights to zero that, plus the eotech is really more for my future 16" build.

to leverage your thread, if you don't mind...

does the number next to width of view at 100 yds mean, the small the number, the greater the magnification? and the larger the number, the less strong the scope is? it sounds to me it is, but just double checking since i notice the scope price goes higher when the width of view becomes smaller at 100 yds

disregard my question on field of view. just answered above by bweise.

10-10-2007, 9:10 AM
Here are a few good links:

Rifle Scope Terms with Pics:

Chatty overview of optics:

Ken Marsh's shooting pages:

General mounts are pretty straightforward, but for ARs, it quickly becomes very complex, due to the wide variety of options available and the mix-and-match nature of AR builds. You can spend quite a lot of money on hardware only to find out it doesn't really work for your intended purposes.

Best bet on getting mounts and rings right is to come up with some ideas that you think will work after reading up, then ask people here to review it. There's lots of good advice around, much of it won the hard way!