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-   -   Those numbers mean something. (http://www.firearmstalk.com/forums/f65/those-numbers-mean-something-37424/)

Shihan 01-26-2011 02:49 AM

Those numbers mean something.
 
I can look at a tire an see, P225/60R16 63H M+S and I know it is a Passenger Tire with a width of 225mm, an aspect ratio of sidewall to width of 60, it is a Radial with a wheel diameter of 16 inches, load rating of 63 with an H speed rating(130mph) and M+S denotes All Season driving.

But if I see, 3-12x50, I have no idea. Break it down for the Layman.

Gatekeeper 01-26-2011 03:20 AM

3-12 X 50 would be
3 to 12 variable power magnification X 50mm Objective lens diameter

4.5-14 X 40 would be
4.5 to 14 variable power magnification X 40mm Objective

etc...

c3shooter 01-26-2011 04:17 AM

And a fixed power scope (like the little bitty .22 scopes) would be 4x15. 4 power, 15mm objective lens.

Shihan 01-26-2011 08:18 PM

How about a little primer on how to choose the proper power for different applications. Let's not be brand specific. Just say I want to shoot 500 yard with a rifle what power would be good.

What about objective lens size? What would I want 30, 40 or more? Would it be similar to a telescope the bigger diameter the more light is gathered?

jpattersonnh 01-26-2011 08:38 PM

Depends on the qaulity of the glass!!! I have old 4x scopes that will do it, and new 4x scopes that it is way past their ability.

DrJason 01-26-2011 08:56 PM

Quote:

Originally Posted by Gatekeeper (Post 429830)
3-12 X 50 would be
3 to 12 variable power magnification X 50mm Objective lens diameter

4.5-14 X 40 would be
4.5 to 14 variable power magnification X 40mm Objective

etc...

What is the importance of the objective lens diameter? Is larger better? As magnification changes does the importance of lens diameter change?

willfully armed 01-26-2011 09:25 PM

larger the objective, the more light that comes in.

jpattersonnh 01-26-2011 09:50 PM

Quote:

Originally Posted by willfully armed (Post 430353)
larger the objective, the more light that comes in.

Not if you use a high powered scope! As you increase magnification it diminishes light.

Gatekeeper 01-26-2011 10:09 PM

Quote:

Originally Posted by DrJason (Post 430322)
What is the importance of the objective lens diameter? Is larger better? As magnification changes does the importance of lens diameter change?

See "Exit Pupil"
Optics - The Advantages of a Large Exit Pupil

The Advantages Of A Large Exit Pupil
By Hugh Birnbaum
A significant characteristic of an optical viewing instrument is the diameter of the exit pupil. The exit pupil is the circular patch of image-forming light the instrument presents to your eye. If you point a riflescope toward a brightly lighted wall or a patch of clear sky (but not at the sun!) and position your eye about 10 inches from the eyepiece, along the optical axis, you will see a bright disc of light in the center of the field. That disc is the exit pupil. The larger it is, the brighter the viewing will seem, because more of your eye will be bathed in light.

You can calculate the size of a scope's exit pupil by dividing the effective objective diameter in millimeters by the magnification. For a 4X 32mm hunting scope, divide the 32mm objective size by 4 and you find that the exit pupil is a generous 8mm in diameter. With a 6.5-20X 50mm target/varmint variable scope, the exit pupil ranges from a large 7.7mm at 6.5X to a smallish 2.5mm at 20X. In a low-light situation, all other factors being equal, a lower magnification setting will provide seemingly brighter viewing than a higher one.

It is tempting to conclude that the largest obtainable exit pupil is the most desirable. But that's not always the case. The catch is that the pupil of a normal human eye opens to a maximum diameter of 5mm to 7mm, depending on the individual, even in extremely dark surroundings. Exit-pupil diameters that exceed about 7mm deliver more light than your eye can accept.

c3shooter 01-26-2011 10:32 PM

Early "night glasses" were binocs with a large exit pupil- matched up to your eyes at night. You got to use more of the light, and could see better in dim conditions.

In GENERAL, the more glass inside the scope, the more light gets soaked up by the scope- but coatings on the lenses, composition of the lens itself and the stickum that attaches one bit of glass to another makes a difference- and large objective (front) lens DOES gather more light- but what happens to light inside scope is another matter.

Then there is color, distortion near edges, field of view, yada yada yada. Like most things, you get what you pay for. There is a reason that a $500 scope is a $500 scope. But frankly, you don't always NEED a $500 scope. Durable and reliable, yes. But for a 30-30 lever?

One simple test of a scope is squaring the box. Zero scope. Then 10 clicks up, 10 right, 10 down, 10 left, then shoot. Still zeroed?

Too MUCH magnification can be bad- dimmer, small field of view- for hunting, at 200 yds, with a 24X scope, I would not be able to find the deer! for 500 yd shots on a groundhog, good scope.


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