Rifle Scope question about tube diameter

[squarles67]

This in reference to a hunting scope so I'm really interested in low light performance.

With a 30mm tube does the increased tube diameter gather any more light than a 1" tube (assuming the same objective diameter) or is all you're gaining increased windage and elevation adjustment range?

What are the other advantages of 30mm tube over the 1" tube?

Thanks

 

[Vern Humphrey]

There are two basic advantages to 30mm tubes. First of all, they sell for higher profits, and second they have more room for adjustments.

 

[Mike1234567]

Tube diameter has no affect on "gathering" light. The incoming light is gathered by the front lens, which may be corrected by other lenses, then the light collimates (the focal crossover point) somewhere near the center of the scope. Then it continues to the eye piece where more corrective lenses are probably used. The image radiates away from the center in opposite directions (the incoming and outgoing image). The only effect the tube has is, as the cone diameter increases (both to the front and to the rear), its likelihood of blocking some of the edge image. What this means is wider diameter tubes allow for a wider field of view. The exit pupil may also be affected.

Edited for clarity. Also, another poster mentioned greater reticle adjustment, which is true. I'm not a scope guy but an old skool photo guy.

 

[squarles67]

First of all, they sell for higher profits

That's the reason for my question, if I don't gain any low light performance it's not worth the extra money to me.

 

[jmr40]

30mm tubes used along with large, 50-56mm objective lenses probably help some. Probably a waste of time with smaller glass.

 

[dubbleA]

There are two basic advantages to 30mm tubes. First is that most will offer greater reticle adjustment and second the tube is physically stronger given the same tube wall thickness over a 1" model.

 

[briansmithwins]

Objective lens power and exit pupil (objective lens size in mm / magnification) determine low light performance. For best low light usability you want a exit pupil of 8mm.

Tube size doesn't enter into it. The bigger tubes can get you more mag range adjust, but you have to decide if that's important to you of not.

BSW

 

[redneck2]

Objective lens power and exit pupil (objective lens size in mm / magnification) determine low light performance. For best low light usability you want a exit pupil of 8mm.

This would be true, assuming all glass was equal. Actually, in the real world performance is very much determined by the quality of the glass and coatings.

I have some very expensive scopes, and some not so good ones. On cheaper scopes, it's almost like looking thru fog or haze if they're cranked up to highest magnifications. Expensive scopes are still crisp and clear.

I'm going on a bear hunt in Canada. Dark woods, black target. I'm getting a Leupold VX-R. I was going to get a Swarovski, and compared it to the Leupold. The Leupold was (much to my surprise) just very slightly clearer , $150 less money, and has the Firefly reticle.

FWIW...it's got a 30mm tube. If you've got a really clear scope, light gathering isn't an issue. I use a B&L 2x7 on my deer gun. I can see thru it well after I could use irons (at dusk).

 

[Bill_Rights]

I've worked a little in optics but haven't looked up the old information for scope-like applications before writing this. But in addition to the positive aspects of larger tube already mentioned, generally, the larger diameter allows a designer to use more gently curved lenses. This, if taken advantage of, gives less loss, less chromatic aberation and better depth of focus. This is true for the glass itself as well as for the coatings. All of this comes from just keeping the angle-of-incidence of the light closer to 90° to the lens surface. Alternatively, the designer could push the angles-of-incidence up to the usual small-tube values and get better performance of some other parameter, such as magnification adjustability range, as already mentioned.

It's a mass of trade-offs. The bigger tube just makes everything easier to get standard performance, or possible to get superior performance. As said, a highly optimized, expensive 1" tube scope could have equal or better performance in one or several parameters than a 30 mm tube scope. But if equally strigently engineered, the 30 mm tube scope would always exceed 1" tube scope performance. But it would be equally possible to achieve mid-level perfomance from a 30 mm tube scope using cheaper components, meaning that the 30 mm scope should be cheaper than the same-performing 1" tube scope, if the cost of the metal is small in both. As someone pointed out, this is unlikely since there is a military or "tacticool" premium price charged for 30 mm scopes. Its all a matter of many design choices. The designer just gets easier choices to achieve the same perfomance in the larger tube.

Seems like the OP was fixated on low-light performance. What optics parameters affect this would require some study. It might be specific to your eyes. Maybe get your eyes measured with this in mind. Then what is needed is a way to know or evaluate how different scopes are designed to optimize (or not) the relevant parameters. That's beyond my pay grade at the moment.

 

[madcratebuilder]

Higher end scopes well have a "Twilight" rating, giving you a way to compare different scopes. 30mm tubes are pretty much main stream, the new high end is 34 and 35mm.

 

[Mike1234567]

I just read another thread in which someone posted that certain scope manufacturers are making 30mm tubed scopes with the very same components as their 1" versions so there is no benefit to the larger tubes. That's just low... but it doesn't surprise me in the least. At any rate, this is just another thing to watch out for.

 

[Haxby]

Inside the main tube of any scope is a smaller erector tube. The lenses in this tube are about 0.5" across, and the light is focused to an area smaller than that.

A 30mm tube has a little more room inside for things like illuminated reticles. When somebody makes a scope with a 30mm tube, plenty of W&E adjustment, and an illuminated reticle, there probably isn't room for an erector tube that's any bigger than they put in a 25.4mm tube.

Twilight factor is a number derived from a mathematical formula. All 3-9X40 scopes have the same twilight factor numbers, no matter who makes them or how much they cost.

 

[Hizzie]

Focusing on overall scope quality and lense coatings will provide low light performance. Like diamonds, quality is more important than size.

 

[squarles67]

Thanks guys

I'm looking at Leupold scopes if it matters. This is for my deer rifle so I'm very interested in low light performance.

 

[Haxby]

For a Leupold to use in low light, look at VXII, VX-R, and VX3 models. These models are fully multicoated. You might as well go with at least a 40mm objective.
A heavy duplex, or the illuminated reticle in the VX-R, will help in low light.

 

[sansone]

I've worked a little in optics but haven't looked up the old information for scope-like applications before writing this. But in addition to the positive aspects of larger tube already mentioned, generally, the larger diameter allows a designer to use more gently curved lenses. This, if taken advantage of, gives less loss, less chromatic aberation and better depth of focus. This is true for the glass itself as well as for the coatings. All of this comes from just keeping the angle-of-incidence of the light closer to 90° to the lens surface. Alternatively, the designer could push the angles-of-incidence up to the usual small-tube values and get better performance of some other parameter, such as magnification adjustability range, as already mentioned.

It's a mass of trade-offs. The bigger tube just makes everything easier to get standard performance, or possible to get superior performance. As said, a highly optimized, expensive 1" tube scope could have equal or better performance in one or several parameters than a 30 mm tube scope. But if equally strigently engineered, the 30 mm tube scope would always exceed 1" tube scope performance. But it would be equally possible to achieve mid-level perfomance from a 30 mm tube scope using cheaper components, meaning that the 30 mm scope should be cheaper than the same-performing 1" tube scope, if the cost of the metal is small in both. As someone pointed out, this is unlikely since there is a military or "tacticool" premium price charged for 30 mm scopes. Its all a matter of many design choices. The designer just gets easier choices to achieve the same perfomance in the larger tube.

Seems like the OP was fixated on low-light performance. What optics parameters affect this would require some study. It might be specific to your eyes. Maybe get your eyes measured with this in mind. Then what is needed is a way to know or evaluate how different scopes are designed to optimize (or not) the relevant parameters. That's beyond my pay grade at the moment.

best description of 1" vs 30mm I have ever read.. thanks Bill

 

[45crittergitter]

Optical instruments do not "gather" light. They simply transmit, with varying degrees of efficiency, light which falls on the lens.

Also as mentioned, scopes with 30mm tubes can contain half again as many windage and elevation clicks as scopes with 1" bodies, according to Leupold. But when the adjustments are set away from center, the optical system is essentially bent, with the erector tube tilted inside the scope. This often results in serious parallax problems, and at the extremes of the adjustment range, each click moves the erector tube less consistently.

Also, a 30mm tube can (but most American scopes don't) accommodate larger erector lenses, for a brighter, clearer, image.

 

[Bill_Rights]

Thanks, Sansone. Others' points were maybe more practical for the buyer concerned with low-light performance. Larger objective lens, high quality glass and coatings and proper exit pupil may be something the buyer can identify and choose, and probably mean something, all other things being equal. I was talking mainly about choices of the engineer or designer, and it might be harder to find out how those got implemented in manufacturing. But I add some perspective.

What I threw out as an off-hand comment

low-light performance....might be specific to your eyes

has got me wondering. For example, I went through several red-dot or reflex sights, sending several back, before I settled on EOTech holographic types. The problem was, I was "seeing" tremendous speckle, streaking, graininess and so forth in and around the aiming dot. I found this distracting and maybe making precise aiming unlikely. I know that I was somewhat "spoiled" by illuminated reticles in regular tube scopes, which appear perfectly "crisp" to my eye. Friends who looked through these same red-dot sights did not complain as much as I did, though we did not have precise language to tell each other what we were seeing. Anyway, the speckle and so forth is still there, to some degree, in the EOTech hologram image, but I find it acceptable because it kinda "averages out" around the whole 65 MOA outer ring of the sighting image. The center dot of the EOTech 65/1 image is as fuzzy as any, but being only 1 MOA (tiny), I can't make out its internal shape so it doesn't distract me as much).

I complained about this red-dot experience to you THR guys, and several people seemed to know what I was talking about. I can search up that thread if interested. At least one or a few of them said that the issue was the make up of my retina (retinas? both of them?). As I recall, the theory was that the arrangement, in my eyes, of rods and cones, blood vessels and optic nerves made me see more speckle than other people. Huh? Wow! Ok, well maybe. At that level, it could even be how my brain processes the signals from the optic nerves. If that's true, it could depend on how much sleep, coffee, food or adrenaline I had affecting my brain at the moment.

Anyway, I was wondering if different people have different low-light perception? I bet "yes". For example, my son is known by coaches to have superior peripheral vision, which gives him an advantage on the basketball court. So the question would be how that maps into desirable scope features for each person, to obtain best low-light aiming? [Or just get night vision, which is probably a whole 'nother ball of wax, plus unsporting for hunting.]

 

[helotaxi]

Night vision unsporting? Hardly. For hunting certain things, it doesn't even begin to level the playing field.

 

[Bill_Rights]

more practical yet....

Helotaxi, Unless you're hunting bats on the wing, I'll not ask further lest we get this thread locked...

All,
Even more practical when it comes to the OP's question about low-light performance is: PRACTICE WITH WHAT YOU'VE GOT. That's what military marksmen and snipers do. Learn your equipment absolutely and train yourself, including your eyes and brain, to a reasonably high level. Then you'll really appreciate better optics.

So, I would say take your existing rifle and optics set-up to a farmer's field or woods at dusk (most ranges are either closed or lit at that time), set up a light brown target (if its deer you're after) and practice sighting against a backdrop of shadowy tree line or grass field (or whatever you typically will see behind your deer). You don't even really have to shoot live ammo (unless my adrenaline hypothesis holds). If you want, have a buddy with a flashlight stand down near the target (chamber and magazine EMPTY!), find your best sight picture, then have him turn on the light so you can see where you were aiming. Try to get better. Borrow and bring other people's rigs to see how they work. This process for a few evenings should be enlightening (endarkening?).

 

[Haxby]

Recap:

A 30mm tube does not gather, collect, or transmit more light than a 1" tube.

"Gather" and "collect" are valid terms for this. They're valid terms for binoculars or telescopes, so there's no reason not to use them for rifle scopes.

Better glass does make a difference.
Better coatings make a difference.

Practicing pointing a gun at your friend in the dark ties for the dumbest idea I ever heard.

 

[MistWolf]

The larger internal diameter of the 30mm tube does allow more light to pass than the smaller 1" tube. However, most makers install the same diameter erector in both which limits the 30mm. It also gives more room for the erector set for windage and elevation adjustments.

If a larger diameter erector set was used, the 30mm tube would pass more light

 

[MistWolf]

It's known that having astigmatism can make the reticles of an RDS look "out of round"

 

[Haxby]

There's a Youtube video where a spokesman for Zeiss says that tube diameter has nothing to do with light transmission.

 

[MistWolf]

That's nice, but I have to go with physics over YouTube.

A large aperture admits more light than a small aperture. That's what the tubes are- apertures. What limits light transmission in a 30mm tube is using the same diameter erector set as the 1" tube uses