1" or 30mm? Which one is better for light transmission?

This is a question that was PM'd to me.

I wanted to post and clarify.

30mm scopes were first made in Europe years and years ago for two reasons.

1. Everything was done by hand and a large tube was needed to be able to build the scope.
2. They are on the metric system.

When we started building scopes in the U.S. technology had advanced some and being on the Standard system we built our scopes with 1" tubes.

The German scopes were and are superior because they use better glass, better coatings and better craftsmanship. Most people assume that bigger is better and that must be the reason why German 30mm scopes are brighter.

It did not take long for U.S. and Asian scope makers to catch on to this and start offering 30mm scopes. It worked for a while but more and more people are learning the truth with the advent of the Internet.

When Leupold first offered a 30mm tube in a hunting scope, they named it the Euro. 30. A competitor dissected one and said, B.S. that scope has 1" guts with a 30mm tube. Leupold's spin doctors quickly changed the name of the new 30mm line of scopes to LR or Long Range and released press releases stating that this new line of scopes has 1" internals with a 30mm tube to allow for more elevation adjustments.

Bottom line is 30mm scopes are 30mm because of the Metric system, they can be brighter than a 1" scope with all other things being equal (# of internal lenses and diameter of objective especially) if the maker takes advantage of the larger internal lenses in a manner that manages the light better (cutting down on distortion and stray light loss). 30mm scopes are also stronger and usually heavier. Biggest advantage is more internal adjustment travel for long range shooting.

However, light transmission is going to based on the size of the Exit Pupil.

Exit Pupil defined:
The size of the column of light that leaves the eyepiece of a scope (usually measured in millimeters). The larger the exit pupil, the brighter the image. To determine the size of the exit pupil, divide the objective lens diameter by the power of the scope. IE; a 4x32 scope would have a 8mm exit pupil. 32/4=8.

All in all, the greater the Exit Pupil, the better low light preformance you are going to have.

I've got one 30mm scope and it is my brightest scope, but is also my most expensive scope. I've always assumed that the larger tube would carry more light, but written data suggests that a 30mm tube won't add any light transmission over a 1 inch tube. As to whether or not that's true....I'll accept what you said as correct and reasonable. As for the exit pupil size, I've read, during research on binoculars, that anything more than about a 5 is wasted on folks with aging eyes. Only the young can benefit from a larger than 5 exit pupil.

That is a common mis-conception as well as a wider field of veiw. Larger maintube contributes toward maximizig the amoutn of internal adjustment in your scope. "More Minutes = More Distance"

Good info man, thanks.

Great post, thanks for the info. I never considered that scope mfg's could/would just put 1" internals into the 30mm tubes. I will pay more attention to the exit pupil size now.

It has happened in the past.

But that has all changed. You should still pay attention to the exit pupil though.

TTT