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Optics FAQ - Please read before posting new topics

The following are some of the most frequently asked questions concerning optics. If you are new to the site, chances are the answer to your question is here. If not, the search button will yield a wealth of information about most any topic. Please excuse the humor, it makes my writing (and hopefully your reading) this FAQ more enjoyable. So, without further delay here we go:

Q: What is the best scope to get for under (insert cost here)?

A: The quality of riflescopes is usually in direct relation to price. The best choice is to buy the very best scope you can afford, instead of buying a poor quality scope and quickly ditching it for the one you really wanted to begin with. If you absolutely can't afford a top quality scope, see the next question.

Q: OK, I can't possibly afford a top quality scope. Should I abandon hope?

A: No, there are several quality scopes available at lower price points. Leupold's Mark 2 series and SWFA's Super Sniper line are two of the better known "budget" optics.

Q: Wow! I really like the new (insert brand name) scope with the huge objective lense, illuminated reticule, mil-dots etc. With features like these, it must be good! Cheap too.

A: Beware cheap scopes with a long list of features. Chances are the quality of the lenses are poor, and the company is hoping you won't notice while you stare into the gaping maw of the monstrous objective (front) lense. Quality of glass is far more important than size of glass. A top quality 40mm objective scope will be brighter and clearer than a cheap 55mm space scope. Again, buy the best you can afford, and suspect any cheap scope with fancy features.

Q: What features should I look for in a scope?

A: A good scope should have repeatable adjustments, high quality glass, ample elevation travel and be durable. Other nice features are tall "target" turrets, a measuring/range finding reticule, illuminated reticule and an first focal plane reticule.

Q: What's a turret?

A: Turrets are the rotating dials on the scope body. Turret types include elevation (impact up/down), windage (impact left/right), parallax, and reticule illumination. Elevation and windage turrets most commonly have 1/4 MOA "click" values, but other values are available, including 1/8, 1/2, 1/3, and 1 MOA. Turrets can also be had with metric measurements for those who want them.

Q: What's a MOA?

A: MOA is an abbreviation for Minute of Angle, a mathematical concept involving degrees in a circle. For our purposes, MOA roughly corresponds to 1 inch at 100 yards, 2 inches a 200, 3 at 300, and so on. This is called "shooter's MOA". So, if a scope has 1/4 MOA "clicks" it will take 4 clicks to move the bullet impact one inch in the desired direction at 100 yards.

Q: How much magnification do I need?

A: How much magnification you really need depends on the intended application for your rifle. If your shooting will be at fixed targets at known distance on the range only (as in long range competition) then the sky is the limit. If you plan to use the rifle for hunting, engaging moving targets at a shooting school, or for "Tactical" competitions, you should consider having a scope with a lower power. The higher the power, the more restricted the field of view, the worse mirage gets, the lower the total elevation travel will be, and so on. Some believe that a good rule of thumb is 1x magnification per 100 yards, other prefer a little more. Look, think, and decide for yourself.

Q: What is field of view?

A: FOV, or field of view, is the amount of the surroundings you can see when looking through a scope at a certain power at a certain distance. A wide FOV is important when engaging non-static targets, who might move right out of your scope picture before you can shoot. That is, if you can even find the target in the first place with your Hubble sized, super-duper 40x magnification scope while searching for your target. Lower power corresponds to wider FOV, generally a good thing, and higher power corresponds to less.

Q: Money is no object, who makes the best scopes?

A: This is very much a matter of opinion. All of the big name makers make excellent scopes in their flagship lines, and the choice becomes simply which features you want more. Two companies particularly well known for best-quality scopes (and the attendant prices) are U.S. Optics and Schmidt and Bender. U.S. Optics will even custom build a scope to your desires. Leupold Mark 4s and Nightforce NXS scopes are also popular.

Q: What the heck is a BDC?

A: A Bullet Drop Compensator, or BDC, is a feature that allows you to simply dial the range to target and engage. BDCs are typically represented by a second set of numbers on the elevation turret above the MOA marks, (1,2,3, etc...) designating hundreds of yards. A BDC will only be accurate under the exact conditions that it was calibrated; that is, the same bullet, muzzle velocity, elevation above sea level, humidity, temperature etc.

Q: What is this stuff about focal planes?

A: This has to do with the position of the reticule inside the scope. Reticules on the first focal plane (FFP) will change size with the magnification, and allow range finding reticules to give accurate measurements at any magnification. Second focal plane (SFP) reticules stay a constant size at any magnification, and range finding SFP reticules are only accurate at one magnification, typically the highest.

Q: What magnification is my mildot reticule accurate at?

A: See the above question, read the manual, and call the company if you're still not sure.

Q: What are M1, M2, and M3 dials?

A: These are designations used by Leupold to signify the value of the elevation adjustments on their Tactical line of scopes. M1 is 1/4 MOA, M2 is 1/2 MOA, and M3 is 1 MOA. M2 and M3 scopes also have a BDC, as explained above.

Q: What difference does tube diameter make? Which is best?

A: Scopes come in several different body tube diameters. The two most common are 1 inch and 30mm. Larger tube diameters allow for more elevation adjustment and generally make for a stronger scope. The downside is the bigger they get, the heavier they are, and the smaller ring selection gets. The most popular tube diameter is 30mm.

Q: My local gunshop doesn't have/can't get the scope I want. Help!

A: The Internet is the answer to your prayers. Scopes are available everywhere. For better pricing on all kinds of gear and good customer service, consider becoming a member and contacting Mel.

Q: OK, I've got my shiny new scope, but those mounts are going to require me to sell a kidney. Are bomb-proof mounts a must?

A: If your rifle is destined for serious use (read: likely to see active duty in a military/police/protection of life setting) then yes. If not, then you can get away with rings and bases that didn't cost as much as your last car payment. Burris XTR rings being a popular example.

Q: What height rings do I need to mount my ________ scope?

A: Read the manual. Consult the manufacturer. Leupold has a chart in their catalog indicating which rings for which scopes on which rifles. If you decide to wing it, just remember: do not allow the objective bell to touch the barrel.

Q: Does my scope have enough adjustment to make it to 1000 yards?

A: This is determined mainly by your scope's total elevation, which should be listed in the manual or on the manufacturer's website. Look at the drop tables for your specific cartridge and figure out how much "up" is required to make it to 1000 yards. If you don't have enough, you may be able to get it with a slanted scope base, such as the 20 MOA bases now popular. To use these, mount the scope, dial 20 MOA down, and then proceed to zero. When you are finished, loosen the screws on the elevation knob cap and position it to read zero. You now have more "up" elevation, and should be able to make it to 1000 with most popular scopes. Consult your scope manufacturer if you're not sure.

Q: Which is better: one piece or two piece bases?

A: This is another matter of personal preference. It makes little real difference. One piece rails will allow for slanted bases and allow you to mount other gadgets like a bubble level, while two piece bases weigh less and allow easier access to the loading port.

Q: OK, I've got it all figured out. I bought the best scope I could find, with a big objective and a slanted base. But now I'm having trouble getting my face on the stock properly. What gives?

A: A good cheek weld (placement of the face on the stock) is important to accurate shooting. The height of the mounted scope combined with the height of the stock's comb determines your cheek weld. Large objective scopes must be mounted high to clear the barrel, and slanted bases raise the ocular lense (the one you look through) even higher. Having a bad or non-existent cheek weld on a precision rifle is a problem. It can be remedied by going with a scope with a smaller objective, on a shorter, non-slanted base. If your scope has 100MOA or more of total elevation adjustment, you should still be fine for 1k. If you must have the slanted base and large objective, get a stock with an adjustable cheek piece.

If you would like to see anything added to this FAQ, please let me know. If you can't find what you're looking for here, try the search button, or failing that, just ask. The friendly members here at the site will be happy to help you.

Stay safe and shoot true.

Bead Drawer
Originally composed July 21, 2006



Disclaimer: The author, this website and its owner and agents assume no liability for the use or misuse of this information. This FAQ shall not be construed as a product endorsement for any company, nor libel upon any company. The views expressed herein are not necessarily the views of anyone. This document is the intellectual property of the author and may not be reproduced without the author's express written permission.

Version history: 1.2
Last Updated: 10/7/09
 

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Ever think of being an author Bead?!


Anyways, you get an A+ :D

Great write up.

dom
 

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gunfan86 said:
Great writing. As a metric person I miss the mil-rad stuff, but that's where the search button is for.

For all of our metric friends, the mildot/milradian stuff is even easier. Milradians is based on a 1000 unit scale, and gee, isn't it convienent that the metric system is 10 based?

Here is the easiest way to estimate range using the metric system:

How many centimeters does one milradian cover on the target? Add a zero, thats the range in meters. No math. I love it.

You can use the same mil relation formula also, or a variation of the above. The metric system is awesome.

MEL
 

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Radians are technically unitless, only a ratio, so you can insert whatever you want for units (ie inches, feet, centimeters, decimeters, the length of your one-legged cousin Billy-Bobs left pinky that was lost up to the first knuckle in a tragic bar fight ;)) Just thought I would add that tid bit
 

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monteboy84 said:
Radians are technically unitless..
"radian" is the name of the unit. It's a measure of arc, used instead of degrees-minutes-seconds. Way easier to work with mathematically.


*edit*
Doh! I see now, you're saying you can estimate range with radians using whatever unit of measure you want, feet, meters, yards, inches, whatever. Yes. Same with degrees-minutes-seconds.
 

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taylorism said:
you're saying you can estimate range with radians using whatever unit of measure you want, feet, meters, yards, inches, whatever. Yes. Same with degrees-minutes-seconds.
Right, because a radian is only a ratio and adds no unit to calculations, a radian is the measure of angle at which the intercepted arc length is equal to the radius of the arc . . . .
 

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<soapbox>

Sorry to everybody, but I figure being perfectly correct is always a good thing.

So here is a little sketch which obviously exagerates the angles involved




So the unit of radian is defined as the arc length/radius Thus, in this figure, the angle of BAC (or BAD) is BD/AB (or BD/AD since the radius is the same in both cases). This number in radians is unitless (for example meters/meters or inches/inches you can't do inches/meters!). In a complete circle there are 2*pi radians.

In shooting what we actually care about is the amount we move on the target. This is represented by the ray BC. To determine the length of BC, we need to know the length of AB (this is the distance to the target). You then take the tangent of the angle (BAC). Thus, the distance on the target which is actually moved is AB*tan(BAC). Recall from high school that tangent(X)=sine(X)/cosine(X).

In shooting we make the "small angle approximation" (don't worry I use it in my PhD research too). We state that cos(X)=1 and sin(X)=X in this approximation. Its good for angles under 30 degrees (thats 1800 moa). Thus, we simplify tan(BAC)=BAC. THESE APPROXIMATIONS ARE ONLY VALID IF YOU USE RADIANS (not MOA). Thats why using radians is easy to figure out motion. Since 1 milliradian=10^(-3) radians, at 1000m, this means that the length of BD=1m (exactly!) and thus BC=1m (using the small angle approximation, its actually a dash more but off by a under a millimeter at 1000m).

Anyway, MOA is the a measure of angle (just like a radian). To be strict, you need to take the tangent of the angle and then multiple by the distance to the target. However, we again use the small angle approximation. If you take 1 moa at 100 yards, you get the 1.047" (inches).

In my opinion, there isn't much advantage to using milliradians unless you are good at measuring things at the target in terms of meters. I still think in inches, so I think I'm hosed on really using milliradians. For my needs 1 moa=1" at 100 yards (or meters) and 1 mrad=1/3" at 100 yards (or meters). However, I think its important to realize where we make assumptions.

</soapbox>

At least I feel better about myself now. Mods, if you don't want to leave this in a optics FAQs thats fine, my ego will survive no problem.
 

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very good, except you should be aware you need two right-triangles back-to-back to properly describe the arc. It's actually one equilateral triangle, which is then bisected into two right-triangles, to use simple formulae to reduce the dimensions. Also, C is on the same plane as D. When i get home I'll have time to post a sketch.
 

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lol I guess I never got around to posting that pic...oh well I think we got enough explanation here
 

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I gave up holding my breath to be honest. I think after you linearize using the small angle approximation it'll produce the same answer if you use 1 or 2 right triangles.
 

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Discussion Starter #20
UPDATED 10/9/09

Change Log:

*Repaired incorrectly displayed characters possibly caused by changes in forum formatting, including fractions, apostrophes, quotation marks, etc.

*Minor grammar and spelling fixes.

*Deleted/modified several passages.
 
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