1" vs. 30mm tubes controversy

[Zachary]

There's something that's just doesn't make sense to me about 30mm tubes.  Specifically, perhaps a 30mm tube does not allow more than a certain percentage of light in.  I.E., if an Elite 4200 has 95% light transmission, then, regardless of the tube diameter, the light transmission is still 95%.

However, if you have a bigger tube, then don't you just multiply the additional area by the same 95%?  

For example, let's say that you look through a 1" pipe that is 1 foot long.  Okay.  Now, let's say that you look through a 1 foot long pipe that is not 1", but rather a whopping 6" big.  More light comes in doesn't it?  In other words, there is more light volume - isn't there?

Now, using that example, let's say that we have an Elite 4200 with 50mm objectives and a 1" tube.  Light transmission is 95%.  We look through the scope, and it is, of course, very bright.

If that same Elite 4200 had, let's say, a 6" diameter tube (which I know is ridiculous, but just bear with me), then wouldn't there be more light volume?  And thus more light?  And thus brighter?

So then, if you multiply 95% x 1" tube = certain number, and 95% x big 6" tube = a higher certain number?

Let's look at it another way.  What if the scope tube was not 1", but rather it was just  a measly 1/4" - kinda like a drinking straw - is the scope just as bright with a skinny 1/4" tube as it would be with a 1" tube?  It can't be, can it?

Believe me, I understand that bigger diameter tubes are stronger and have more elevation, but it has to allow more light, right?

We all have our opinions, whether it's based on common sense (at least what each of us believes to be common sense) and/or personal experience.  However, there has to be a a true optics expert in this field that can give us a definite answer.

What do you guys think?

Zachary

[Steelhead]

http://www.24hourcampfire.com/ubbthreads/showflat.php?Cat=&Number=283420&page=&view=&sb=5&o=&fpart=1&vc=1


This is a cut and past from the above link by John Barness.

Contrary to popular belief, 30mm scopes are not brighter than 1" scopes. The only reason they would be is if they allowed for a larger exit pupil at all powers. But this only occurs when a 30mm scope is set on magnifications below about 5-6x, depending on the objective lens--at which point the exit pupil is larger than needed by the human eye anyway.

Above about 5-6x, the exit pupil is the same size as a 1" scope with the same objective size. The reason? At these magnifications, the light-band isn't controlled by the scope tube. Instead it's traveling through the middle of the lenses.

The reason the top-grade European 30mm scopes appear so bright is quality glass. This can be matched, however, by quality glass in any 1" scope.

The real advantages of 30mm are two-fold: a slight increase in strength (a wider tube is stronger than a narrower tube, all else being equal), and greater range of adjustments. The last, however, is often negated by the use of larger lenses inside 30mm tubes. These don't provide a brighter image, because of the phenomenon described in the first paragraph here: At higher magnifications the light is traveling through the center of the lenses anyway. But the do provide good advertising copy.

Advertising--expecially by one particular firm--is the reason the 30mm-is-brighter myth got started. But the real reason many European scopes have 30mm tubes is standardization. As in America, early Euro-scopes had diameters all over the place, but eventually they settled on 30mm (just as we settled on 1") simply to make manufacturing easier, especially of mounts.

If you want a nice, bright, lightweight scope many manufacturers, both in European and elsewhere, make high-quality 1" scopes that tend to be noticeably lighter than 30mm scopes.

[Daniel]

Ditto what John Barsness said.

[bgjohn]

What about a larger field of view? :?
JM

[Dave in WV]

Last year I emailed several scope makers and asked them about this. What I got out of the asnswers was IF the proper LARGER internal optics were used in a 30mm tube it will be brighter. Many 30mm tube scopes have 1" tube sized internal lens and are not brighter. I do not claim this info to be correct but it does seem sound. The light transmission is controlled by the quality of the glass, coatings, design, and workmanship. The exit pupil does not control brightness. If is does then why do the European scope makers use twilight factor to express brightness? Using twilight factor, the higher the magnification , the higher the twilight factor.

[Graybeard]

Laws are fact. Theories are someone's idea that has yet to be conclusively proven.

There are certain optical laws that are incontrovertiple and cannot be changed. There are no free rides and all optical instruments are a result of compromises made by the manufacturer based on where in the market they wish to place their product.

Quality of glass and coatings is the primary determinor of brightness. At every glass to air surface you lose light due to scattering. Coatings can reduce that loss but can never completely eliminate it. The most useable light goes thru the center area of the glass and thus the cheaper scopes use glass not as well polished to the edges to save money with minimal loss of brightness and image quality. BUT make no mistake you can see that difference out near the edges of viewing area.

Many (not all) makers of 30mm tube scopes use internal lens no larger than those in one inch scope tubes. One EVEN places baffles in both to limit the path of the light to the more highly polished center section of their glass. Now what should this tell you about their glass? If the diameter of the internal lens falls below the theoritical exit pupil diameter found by dividing TRUE magnification into TRUE objective lens clear aperture you likely will reduce that exit pupil and brightness both. This applies no matter the tube diameter.

European scopes differ or in the past did at least from American scopes because of the difference in the way game laws read. In most European countries game laws allow you to hunt as long as you can see to shoot. You'll have a guide with you who says when it is time to knock off. So on a moon lit night with optics up to the task you can hunt right on thru the night. In America you cannot except in TX for hogs and in some places for varmints and predators.

So the Europeans want huge scopes with 30mm tubes and the largest internal lens they can get. They want monster objectives and high powers to allow a decent exit pupil even at those high powers. Yes IF (BIG IF) you have an exit pupil of 5 or more at the power you are using more power does allow you to see better in the dark. BUT you MUST have that exit pupil of 5 or more preferably about 7 for best night vision to allow more power to be useable and helpful.  The Europeans also want a big bold crosshair to better be seen in the low light at night. That's why they place their crosshairs in the wrong plane and they are magnified at higher powers. Just the oppposite of what most American hunting calls for.

Anyone who actually thinks they NEED a huge objective high power scope for American hunting under NORMAL American hunting laws is kidding themselves. Most hunting is daylight to dark or 30 minutes before and after official sunrise/sunset times. Any quality glass with quality coatings in the 2-7 to 3-9 range with a 36-40 mm objective is plenty bright enough for such hunting. Even in TX at night hunting hogs IF the moon is out and IF you aren't way back up under a bunch of trees such scopes still do fine. The Bushnell Elite 4200 1.5-6 is one super scope for such hunting. Even you use just about any kinda light for your night time hog or predator hunting such scopes are still all you need. If you can't place your bullet accurately at 9X then you're too danged far from the game to be shooting at it anyway. There is not a big game rifle at my house that wears a scope with more than 9X at the upper end. Most wear lesser power scopes and 40 mm is the largest objective size on them. To date I've never failed to get a shot at legal game during legal shooting hours as a result.

GB

[Daniel]

Well said, Greybeard.

[Cabin4]

I look at the tube vs light issue in a very simplistic manner:

The human eye is capable of accepting approx 5mm of light. So if you have a 20mm tube and 20mm objective lens with the scope set on 1 power, your eye is receiving 20mm of light but can only accept 5mm of what's it receiving. Turn this same scope up to 2power and your receiving 10mm of light (20mm / 2 power = 10mm of light). Again, your eye will only accept 5mm of light. Still more than enough light. Turn the scope up to 3 power and you get 6.6mm of light (still more than enough). Up to 4power and your at 5mm, still at max light for the perfect eye.

My example scope here is a Leupold VX2 1-4x20 it has a 20mm tube. Its an easy one to give this simple demonstration. I think all is the same when using a 30mm scope tube just adjust the formula for 30mm tube.

Objective lens size has more to due with FOV than with light as I understand it. Not 100% sure.

[GBO MGMT]

My example scope here is a Leupold VX2 1-4x20 it has a 20mm tube. Its an easy one to give this simple demonstration. I think all is the same when using a 30mm scope tube just adjust the formula for 30mm tube.

Actually the tube is one inch. The clear aperture of the objective lens is what is 20mm.

Objective lens size has more to due with FOV than with light as I understand it. Not 100% sure.

Objective lens has not one iota of impact on FOV. None whatsoever. There is an optical triangle composed of three elements. 1. FOV  2. Eye Relief  3. Magnification.

Change any one of them and you must alter the others. If you want max FOV you must give up something, either magnification or eye relief. If you want eye relief as on Leupold scopes you must give up either magnification or FOV. Leupold generally gives up a bit of FOV for more eye relief. This is the reason you have more FOV at lower powers, you give up the magnification and get more FOV and often more eye relief both in variables.

GB

[Dave in WV]

There is more to gain from a larger exit pupil than just gathering light. The larger the exit pupil, the more out of alignment you can have your eye to scope and still get a good picture. A large exit pupil is a good thing. You just have to decide what you are willing to give up to get it.  :wink:

[Zachary]

For me, eye relief are more important that FOV, but that's just me.  Also, I think that for scopes over 12x power, I prefer 50mm  objectives because I can have more eye alignment.

Zachary

[ercjr2001]

does eye alignment have anything to do with parralex?
If so how much?

[Dave in WV]

When the parallax is off enough, changing eye alignment will show a change in reticle position in relation to the target. Changing eye alignment doesn't change parallax. To keep it simple, parallax is the distance the reticle appears to be projected on the target.