Busting the myths.

Riflescope brightness is not as big a deal as advertising makes it out to be.

Differences in brightness from scope to scope are often undetectable to users.

Some features credited with brightness don’t even contribute.

Some high-end scopes aren’t as bright as some costing half that.

Maintaining a sharp image is as important as raw brightness. A sharp image at any brightness level looks “brighter” than a softly focused image. Resolution is a critical ingredient for making images seen through a scope appear brighter.

As for the wider main tube contributing to brightness, forget it. Doesn’t work that way. Regardless how much light enters the objective “window.” The higher the magnification, the less light that gets out. The amount of light that exits the scope at the eyepiece depends on the power level. Both objective lens and magnification work together to create the beam of light that exits the eyepiece. It is called the Exit Pupil (EP.) You can see it by holding a scope at arms length and pointed it at a bright surface. The little circle of light you see in the eyepiece lens is the EP. If you have a variable power scope, turn the power ring and watch the EP enlarge and shrink as powers goes down and up. The lower the power, the larger the EP and the more light that exits the scope.

While EP matters, extremely large EP does not because its effectiveness is limited by our own pupils. The human pupil opens (dilates) to about 7mm max. But this doesn’t happen until it’s nearly dark. In full daylight our pupils shrink to about 2.5mm. On cloudy days they might be opened to around 4mm. Place a 5mm diameter beam of light in front of your 4mm pupil and the extra 1mm rim just bounces off your iris. So why bother with a 50mm objective?

The magic hour for hunting is often the last few minutes of legal shooting light a half hour or more after sunset. Our pupils might then dilate to 6mm. They could use all of the 5mm EP and 1mm more. So step up to a big 56mm objective and what do you get? A 5.6mm EP. Not quite the 6mm you could fully use. You’ll need a 60mm objective at 10X to get the full 6mm EP. And if you want maximum brightness at the last minute or two of legal shooting light, you might need a 7mm EP scope. To get that, of course, you’d need a 70mm objective at 10X.

I’m not enough of a precision shooter, especially in dim light conditions, to nay say his observations.  Hunters can weigh in on this.  The most expensive scope I have costs around $600.