Explain scopes to me please

[thewillweeks]

Hey guys,
I've hunted for years, both with iron sights and with scopes but I've never actually bought a scope separate from a rifle (borrowed or the scope came with the rifle, etc). I understand the basics of magnification (I think) but could someone explain to me the benefits/costs of having a bigger tube?

I go to shop for scopes and I see 40mm and 50mm tubes on scopes with the same magnification marked on them, what's the practical difference? Also, is one preferred for mounting on an AR? I'm looking to put one on top of my Colt LE6900 and I'm not sure whats the most appropriate for my rifle. Also, can someone suggest appropriate magnification ranges for a .223? Thanks guys and gals!

 

[scythefwd]

the tube is the same size.. what you're talking about is the objective lens... The big one up front. The larger the objective lens, the brighter the scope will be at dawn and dusk usually.

 

[greyling22]

tubes come in 1" and 30mm. I'd stick with 1" because it is much more common, But probably you mean the objective lens (the front part of the scope)

theoretically, a bigger lens up from (50mm) will allow a scope to gather more light and be brighter and allow you to shoot longer.

In practice, the quality of the glass and coatings matters more than the size of the lens and a big lens just adds weight and bulk.

for magnification, how far are you shooting and how well do you want to see it? a 3-9x scope will allow you to see and hit a baseball at 200yds, but probably will not allow you to see .223 bullet holes on a paper target at 100yds. (at least I can't. but I do not have very good eyes)

 

[TTundra]

You're going to get lots of perspectives and opinions as well as facts from various users. Scopes have their foundations and then have an ever changing feature list. This is a nice article written by a guy at opticsplanet, hes hunted around the world and knows his stuff. But its a general guide to scopes and how to choose what you want/need. Its a few years old, but it will be a nice spring board for further questions you will have:

http://www.opticsplanet.com/howto/how-to-choose-a-riflescope.html

 

[HankB]

The total amount of light falling on a 50mm objective lens is greater than what falls on a 40mm objective lens - all else being equal, if the 'scope is properly designed, this means more light will come out of the eyepiece, making the 'scope look brighter.

The most common 'scopes today have 1" or 30mm tubes, and a few are made with 34mm tubes. Some people claim that larger diameter tubes will pass more light; these people are wrong, as photons don't flow like water. The real advantage of larger diameter tubes is that they allow for more windage and elevation adjustment. A secondary benefit is that they allow the optical engineer more freedom in design and placement of the 'scope's internal lenses.

As far as what's most appropriate for an AR . . . well, it depends on how accurate your rifle is and what you're going to use it for. An extremely accurate varmint rig used for shooting prairie dogs 'way out there might benefit by a target-quality glass up to 20x or so. On the other hand, an awful lot of ARs have zero magnification illuminated sights like an Eotech and serve their users just fine.

 

[j1]

Most magnify the object and make it brighter making it easier to hit.

 

[Krusty783]

'Appropriate magnification range' depends on you and what you're trying to do. Anything less than 100 yds and open sights or red dots are probably sufficient unless you are target shooting or tuning handloads.

Anything over 20x is probably overkill for an AR unless you are prairie dog hunting. 2.5-10 or 3-12 scopes should serve well for mid-range hunting applications. If you want to retain more close range capability, there are some good 1-5/6 scopes out or even 1-8 if you're willing to pay for them.

 

[jmr40]

The larger the objective lens, the brighter the scope will be at dawn and dusk usually.

Partly correct.

The brightness of the scope is determined by the quality of the lense. The amount of light that comes through a scope is determined by 2 things. The objective size, and magnification.

If you take the front objective size of a scope and divide by the scopes magnification you determine the diameter of the light beam that leaves the rear of the scope. This does NOT determine the brightness, just the size of the cone of light. High quality glass will allow the beam of light to be brighter than low quality glass. A good quality 32mm or 40mm scope will be far brighter than a lower quality 50mm scope.

A scope with a 50mm objective set on 10X and another scope with a 40mm objective, and equal quality glass, set on 8X will both allow a 5mm beam of light to hit your eye. Both let in exactly the same amount of light at those settings. The 50mm scope will allow a larger beam of light through if set on lower magnifications, but most human eyes will only open up to 5 or 6mm. Any more light is wasted and cannot be used.

In short a 50mm objective will allow slightly more useable light than a 40mm scope only when the magnification is set between about 6X up to about 8X. With less magnification the 50 lets in more light, but the human eye can't use it. At higher magnifications they both suffer in low light.

On an AR a 1-4X20 is all the scope you need. With a 20mm objective set on 4X you let in exactly the same light as a 10X scope with a 50mm objective. You don't really need any more magnification and it will be plenty bright in low light situations, especially on the lower magnifications.

 

[bush3755]

While the old "relative brightness" formula:

Objective diameter in mm divided by magnification then squared (50mm /10X =5, 5 x 5 = 25, relative brightness = 25)

...applies to telescopes, binoculars, camera lenses and scope sights, it only refers to the amount of light entering the objective lens at their front and its reduction by its magnification with no loss by lens glass type and their coatings. The amount of light lost passing through each lens will be as much as 3% to 6% in poorly coated ones to .1% to .2% in the very best ones. Therefore, two 10 x 50 scopes with totally different lens coatings on each of ten lenses inside them could have anywhere from 1% of the light lost that goes into the shooters eye to as much as 60%.

Magnification doesn't make the target appear brighter, just bigger. Rifle scopes are exactly like camera lenses. A distant object will be the same brightness on the image plane with the iris set to f/4 for a 10mm lens as a 100mm lens; both having the same lens coatings. While the camera front lens will be ten times bigger (25mm versus 2.5mm diameter) and make the object image that much bigger with the 100mm one, the amount falling on a given image point will be the same in each. The same shutter speed can be used.

More magnification for a given objective diameter means less light with the same light loss amount for all the lenses. So the target always is dimmer by some amount. Few people can easily tell the difference in a 20% difference in image brightness unless they're switching between two scopes back and forth with no more than a couple seconds delay between them.

Therefore, a 10x40 scope with well coated lenses will have a brighter image seen by the aiming eye than a 10X50 one with poorly coated lenses.

Here's a link to Canon's web site explaining light loss in camera lenses that applies to all lenses. Good technical explanation:

http://www.canon.com/technology/s_labo/light/003/03.html

 

[Hookeye]

Also remember the "optical triangle".

View attachment 724645


I run 40mm objective stuff because I like my stocks to fit.
If need be, will make a cheekpiece for proper cheekweld.

Fairly recent ad in hunting mag.......shows some guy with a big scope, with over an inch of clearance under the objective..........freakin' chin barely touching the comb. Yeeesh.

 

[JSH1]

What I want to know is how much better is a $500 scope compared to a $300 or $100 one. I doubt the $500 scope is 5X better than the $100 one. Is it even 5%?

I was looking at scopes last week and asked the salesman the difference between a Leupold VX-1 vs VX-2 vs. VX-3. What he said was each time a new new scope comes out or improvements are made model names get shuffled. So today's VX-1 is the same as a VX-2 from a couple years ago, etc, etc. I personally couldn't tell a bit of difference between them looking through them in the store.

 

[Lord Teapot]

Partly correct.

The brightness of the scope is determined by the quality of the lense. The amount of light that comes through a scope is determined by 2 things. The objective size, and magnification.

If you take the front objective size of a scope and divide by the scopes magnification you determine the diameter of the light beam that leaves the rear of the scope. This does NOT determine the brightness, just the size of the cone of light. High quality glass will allow the beam of light to be brighter than low quality glass. A good quality 32mm or 40mm scope will be far brighter than a lower quality 50mm scope.

A scope with a 50mm objective set on 10X and another scope with a 40mm objective, and equal quality glass, set on 8X will both allow a 5mm beam of light to hit your eye. Both let in exactly the same amount of light at those settings. The 50mm scope will allow a larger beam of light through if set on lower magnifications, but most human eyes will only open up to 5 or 6mm. Any more light is wasted and cannot be used.

In short a 50mm objective will allow slightly more useable light than a 40mm scope only when the magnification is set between about 6X up to about 8X. With less magnification the 50 lets in more light, but the human eye can't use it. At higher magnifications they both suffer in low light.

On an AR a 1-4X20 is all the scope you need. With a 20mm objective set on 4X you let in exactly the same light as a 10X scope with a 50mm objective. You don't really need any more magnification and it will be plenty bright in low light situations, especially on the lower magnifications.

considering anyone who bothers to practice twice a month can accurately shoot a 16inch ar15 out to 500yards with iron sights, saying a 4x scope is all anyone needs is really quite incorrect.

 

[Lord Teapot]

What I want to know is how much better is a $500 scope compared to a $300 or $100 one. I doubt the $500 scope is 5X better than the $100 one. Is it even 5%?

I was looking at scopes last week and asked the salesman the difference between a Leupold VX-1 vs VX-2 vs. VX-3. What he said was each time a new new scope comes out or improvements are made model names get shuffled. So today's VX-1 is the same as a VX-2 from a couple years ago, etc, etc. I personally couldn't tell a bit of difference between them looking through them in the store.

if you want a decent item but dont want to pay a fortune, go with nikon. not cheap not expensive, gets the job done and has good lense quality.

 

[Hookeye]

FWIW I run a 2-7X on my 16" AR

For yote to 300 I find it perfect.
Small enough it looks right too.

If you're gonna punch paper at 100 most of the time, I'd opt for 12X (minimum).

If running a heavy/long AR.........for target and hunting, maybe a 6-18X.
But walking from stand to stand over big fields with snow.............yeah, you'll ditch that target rig and build a 16" with smaller glass

 

[JSH1]

if you want a decent item but dont want to pay a fortune, go with nikon. not cheap not expensive, gets the job done and has good lens quality.

Nikon scopes still range from $100 to $1000. Picking a brand doesn't answer the fundamental question of what a buyer gets for the additional dollars spent between one model and another.