This is off topic but this is where I hang out

Most of you already know this but it will be helpful to new shooters

There are two basic kinds of rifle scopes for sporting purposes, fixed power and variable power scopes.

Fixed power scopes:
Fixed power scopes have the magnification set by the manufacturer and can not be changed.
Example 4x - 32mm scope:
The 4x is power or magnification, which means it will magnify an object up to 4 times larger than you could see with the naked eye.
The 32mm is the objective lens diameter, which is measured in millimeters. The larger the objective lens diameter, the more light it will gather brightening the view.

Variable power scopes:
Variable power scopes the magnification can be adjusted according to the distance of view needed by the user by simply turning the power ring at the back of the scope.
Example 4-12x - 40mm scope:
The 4 - 12x is power or magnification, which means it will magnify an object from 4 times larger than you could see with the naked eye and by turning the power ring it will adjust up to 12 times larger than you could see with the naked eye.
The 40mm is the objective lens diameter, which is measured in millimeters. The larger the objective lens diameter, the more light it will gather brightening the view.

Objective lens:
The objective lens is the lens in the front of the scope, the larger the diameter the more light gathering ability it has.

Adjustable objective lens:
The Adjustable objective lens has the ability to correct parallax at given yardages to keep the scopes on target zero for all yardages regardless of the shooters eye alignment in the scope.

Exit pupil diameter:
The exit pupil diameter is the shaft of light exiting the scope toward the scope users eye, this is expressed in millimeter measurement. It is also the true measure used to rate the brightness of a riflescope's sight picture. The larger the diameter the better it is for low light conditions.

Field of view:
Field of view is the measure of how much area you can see through your scope at 100 yards, generally, the higher the magnification, the less the field of view.
Example field of view of 40 feet:
With a field of view of 40 feet, simply means at 100 yards with a target in the center of the scope you will be able to see 20 feet to the left and 20 feet to the right of the target.

Eye relief:
Eye relief indicates the distance between your eye and the scope, which allows you to achieve the scopes entire field of view.
Example eye relief of 3"
An eye relief of three inches is simply your eye is 3 inches from the scope and your able to see through the scope its entire field of view.

Parallax:
Parallax is a condition that occurs when the image of the target is not focused precisely by misalignment of shooters eye on the reticle plane. This condition exists in all scopes and accounts for more inlarging of rifle group sizes than anything else. Parallax is visible as an apparent movement between the crosshairs and the target when a shooter moves their head and changes eye alignment in the scope. The higher the magnification the more visible this is, a good high power rifle scope will have an adjustable objective lens to correct this at all yardages

Jules, good post. Somthing you should add to this is the coatings on the optics. This is the #1 thing I look at on scopes. If you don't have the lens coatings let me know, I have a list of them, somwhere................................
Jeff

Your right Jeff. WOW! there are so many different types.
Lens coatings play an important role in getting the light gathered at the objective end of the scope transmitted through the ocular end to your eye. The lens coatings are partially responsible for delivering a brighter and higher contrast image. Although I have plenty of multi coated lenses "witch are very good" Fully multi coated lenses are the way to go.

Eventually, after looking at many different optical devices, most of us begin to wonder about the coatings that are applied to the lenses. We see "ruby coated" binoculars sold all over ebay, and when we flip through the Orion catalog we see lenses that are "coated," "fully coated," "multi-coated" and even "fully multi-coated." What does all that mean?

Coatings are applied to lenses for one overriding purpose, and that is to increase the lenses ability to transmit light. A plain piece of glass can reflect up to 15% of the light that falls directly on it, and as the angle of incidence increases, so does the reflectivity. In fact light is reflected back towards the source every time it goes across a boundary between two surfaces. Such as between air and glass, or between two types of glass.

When you consider that most modern lenses for telescopes have at least two elements, with some having up to four, and most eyepieces have at least three elements, some with up to six, if you do the math you soon realize that unless something was done, you'd end up losing most of the light that hit your lens.

That's where coatings come in. Coatings are magical in a way. In fact the more you learn about optics and the nature of light, the more magical they seem. But they work. The basic idea of coatings has to do with exploiting the wave nature of light in such a way that you can cause destructive interference in the light waves reflected off the surface.

Think of it this way. If you have a cable tied between two trees and you "twang" it, you will start a wave going between the two trees. If someone else "twangs" the cable at the same time, the two waves will either add together (constructive interference) and produce a bigger wave, or they will cancel each other out (destructive interference) producing a much smaller wave. If you can get precise enough, one wave can completely cancel out another.

In the same manner if you can get light to reflect off of two surfaces in such a way that the reflecting waves cancel each other out, the light energy that would have reflected instead has to go through the surfaces. This is the basic idea behind coatings on lenses. Usually you see lenses coated with Magnesium Fluoride because it is easy to use and is durable.

But if you only coat the outside surface then you only stop the reflections at that surface. Remember how many surfaces we have to deal with? So instead you want to coat each lens surface, or have a "fully coated" lens. Obviously a fully coated lens will transmit more light than a simple "coated" lens.

Okay, but what about "multi-coated"? Well, it turns out that a simple coating works best for a single wavelength of light, with different wavelengths being affected less, and some not being affected at all. Well, with some fancy computer modeling you could see that if you apply multiple coatings of different materials to a lens, then you can cancel out multiple wavelengths of light, improving the lens abiltiy to transmit any color. These are "multi-coated" lenses. And using the same logic as before, if you have every surface multi-coated, then you have a "fully multi-coated" lens. Which are obviously the best kinds to have.

Back to those "ruby coated" lenses then. What's up with that? Well, from what I can tell, ruby coated lenses are pure marketing gimmick. If you think about it for a minute you should realize that if a bright "ruby" red light is being reflected from the lens, then that much red light is not going through it. This results in an image that is disproportionately green, yellow and blue, giving an overall greenish cast to the view through the binoculars.

A coated or fully coated lens usually reflects a dark blue light back to the viewer. So if you use a white flashlight and shine it into the lens, a dim blue image should be reflected. A multi-coated or fully multi-coated lens should have an even dimmer image than the coated lens, and the tint will be more greenish than blue. Of course there are other ways to make a lens reflect blue or green light, so be careful out there and deal with reputable companies as much as possible. And the next time you are trying to figure out why one eyepiece costs $25 and another costs $50, check out the fine print and see which are "fully multi-coated" and which are simply "coated."

Jeff, if you have all the different types of coatings please add them in.

[ 05-03-2003, 18:35: Message edited by: Jules ]

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[ 05-03-2003, 18:34: Message edited by: Jules ]

Types of coatings>>
Coated - A single layer on at least one lens.

Fully-Coated - A single layer on all air-to-glass surfaces.

Multi-Coated - Multiple layers on at least one lens and all surfaces are coated at least once.

Fully Multi-Coated - Multiple layers on all air-to-glass surfaces