More Optics Tips

Revelation Chap 20:1-6 KJV "And I saw an angel come down from heaven, having the key to the bottomless pit, and a great chain in his hand. (2) And he laid hold on the dragon; that old serpent, which is the Devil, and Satan and bound him for a thousand years, (3) And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that, he must be loosed for a little season, (4) And I saw thrones and they that sat upon them and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshiped the beast, neither his image, neither had received the mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years. (5) But the rest of the dead lived not again until the thousand years were finished. This is the first resurrection. (6) Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ and shall reign with Him a thousand years"

I have already established that I think most of us have scopes mounted on our rifles with too much magnification. For most big game hunting, I like 1.5X5X32, 1.5X6X32, 2X7X32, 2X7X35, 2X7X40, and yes the 3X9X40. I do not see the need or desire to have a scope with a bigger objective lens than 42mm or more magnification than is given by the 3X9X40. My feeling is that scopes like those listed above, mount low over the bore, give you faster target acquisition, a larger field of view on dangerous or running game,, all the brightness most of us ever need , and they don't mess up the ergonomics and handling abilities of the rifle. Last but not least, they just plain look good and add a sense of balance to the gun their mounted on. If you hunt prairie dogs out west, the above does not apply.

That being said, all other things being EQUAL, the larger the objective lens on a scope, the more light it allows in and the brighter the target will appear.

I think the catch to it, is all other things being equal:

Remember that we already talked about exit pupil, and relative brightness. The exit pupil of a scope is the diameter of the visible image that exits the eyepiece lens. To determine that, you divide the entrance pupil of the objective lens by the scope's magnification and then the relative brightness is that number squared.

On a typical scope say of 2.5X10X50, it looks like this: At 10X divide the scope's exit pupil (50mm by 10 ) and you get 5.0mm exit pupil. Relative brightness would then be 25. (5.0 times 5.0).

This should make a 50mm objective lens scope brighter than a 40mm objective lens, however the calculation above only works if the actual effective aperture of the scope in question is the same as the diameter of its objective lens. In other words on a less expensive scope, even though it has a 50mm objective lens, it may transmit light from only a 40mm portion of it center.

Just because you paid for the 50mm objective lens, does not necessarily mean your transmitting more light.

How does one test whether or not a particular scope is utilizing the full light transmitting properties of its objective lens? You can perform a simple test with a flashlight and a blank piece of white paper, along with a pencil and a ruler with a millimeter scale on it.

Shine the flashlight through the scope's eyepiece, while holding the blank sheet of white paper over the objective lens. There will be a circle of light projected on the paper. This circle marks the effective aperture of the scope which is the amount of light it actually allows through it.

Mark the edges of the circle of light and measure it with your ruler. If the circle of light is measurably less than your objective lens, it is not transmitting light from its full diameter. You may find that a quality, fully multi coated, high quality polished lenses, 40mm objective lens scope transmitting light from the full 40mm lens, actually appear as bright or brighter than it 50mm counterpart.

The human eye's pupil diameter varies from 2.5mm in bright sunlight to apprx 7mm in total darkness. Let's take a look at the Weaver Grand Slam 1.5X5X32 scope I am mounting on a Ruger model 77 Mark II in .350 Remington Magnum. At 5X the scope's exit pupil is 6.4 (32 divided by 5) and its relative brightness is 40.96 (6.4X6.4). This is a very bright scope, with a large field of view, lots of elevation and windage adjustment built in and a fine choice for a .350 Remington magnum. It also mounts low over the bore and makes target acquisition much quicker.

Dan
www.deer-hunting-information.com