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Light Transmission

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/21/2005 at 11:32
Chris Farris View Drop Down
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It is impossible for any scope to "gather" light. It can only transmit existing light. And, regardless of advertising claims you may have heard, there is no riflescope made that can transmit 100% of available light.

As light enters the objective end of the scope, before it reaches your eye it passes through several lenses. Each lens absorbs a small quantity of light. Residual reflection from the individual lenses will also prevent a certain amount of light from passing through the scope. In addition, undesired reflections within the metal tube can hinder the quality of the viewed image and the transmission of light.

Each lens has two surfaces. Thus, the total number of lenses within a scope (a variable-power scope can have between seven and ten) is multiplied by two, then multiplied by 0.25% to determine the amount of light lost in the transmission. Simple multiplication is not accurate, however, as each succeeding lens progressively reduces the total amount of transmitted light. It is a favorite technique of some scope manufacturers to claim light transmission values of nearly 100%. Of course, they're measuring the first objective lens only, conveniently forgetting about the other eight or nine!

Any higher transmission levels are physically impossible to achieve with current technology, and claims to the contrary are to be discounted. What does light transmission mean in practical terms? An average scope may transmit 85% or so, and inferior scopes substantially less. The human eye can distinguish transmission differences of 3% or more. Consequently, there is a very real difference in what you can see through a superior scope versus run-of-the-mill optics.

The very best rifle scopes human beings can create will transmit to your eye—under perfect conditions—a maximum of 94.5% to 95% of available light. There are but a handful of scope companies remaining that produce optics approaching these levels, Schmidt & Bender being one of them.

Under hunting conditions, when you might be trying to distinguish a target at absolute last light, these differences can be critical. It can determine whether you bag your game or whether you have long since called it a day.

 

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article courtesy of http://www.schmidtbender.com/

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/21/2005 at 12:46
koshkin View Drop Down
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A good article all in all.

 

A couple of comments though.

 

No mention is made of wavelength of light.  Our eyes have different sensitivity at different wavelegnths.  The claim that a human eye can only detect a 3% difference in brightness is incorrect and depends on a number of factors: wavelength, total light intensity and ambient illumination are the ones that come to mind.  For example, in a low light environement, a human eye can resolve slight illumination differences a lot better than in bright sunlight.

 

Also, perceived brightness of a scope depends on the resolution of the image.  I think Dail Clifford has once posted a lengthy discussion of transfer functions.  I was too lazy to go through it in detail, but Ihave some exposure to these matters through my work (I am an optical physicist and work with light sensors for various military and astronomy applications).  It all boils down to this: a clearly defined picture with sharp edges will seem brighter to you than a hazy one (Leupold newly released filters utilize that phenomenon).

 

All in all a good article though.

 

Ilya

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/31/2005 at 15:09
Chris Farris View Drop Down
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