The usual answer is No, the amount of light gathered is dependent upon the size of the objective (front) lens, and the amount that reaches the viewer’s eye depends on such things as magnification and lens coatings and glass quality.

In researching that question recently, though, I ran across a discussion by member jasonfaz on the Sniper’s Hide forum. In his second post there he goes into a lot of technical talk about how a larger tube can improve light transmission and says that the answer to the question isn’t always a simple “no.”

His comments are really too long to post here, but if any of our optical authorities would care to make the effort of reading them, I’d be curious about their reactions.

https://www.snipershide.com/sh...transmission.228561/

Interested to read the commentary on this one.
Hoping NikonUser pops in for some comments.

I specifically went with a 50mm objective to get as much as I could on my Tikka, since, as a hunting rifle, there are dawn & dusk possibilities.
Also went with a 4-20x, because my eyes suck.

Both were a massive improvement over the 3-9x40 Simmons on my 336.

quote:

Originally posted by P250UA5:
Hoping NikonUser pops in for some comments.

He already did -- 8 years ago.

fritz, I am sure, could have answered this.

In a nutshell, tube size makes no difference in light transmission. I will add a little caveat that this applies to the vast majority of riflescopes that I know or have heard about.

Now for a bit of an explanation. It is absolutely correct that a bigger lens will let through more light. That is why the size of the objective lens rules the amount of light coming into the riflescope. By extension, you would think that the bigger diameter of the main tube would contain bigger internal lenses that would also pass through more light. But that's not how riflescopes work.

A riflescope is a different optical device than any other ordinary thing like a telescope, spotting scope, camera lens, microsope, etc. The riflescope has within the main tube, another tube called the erector tube. This tube goes from just in front of the adjustment knobs, all the way to the end of the main tube, before the eyepiece.

At the front of the erector tube, you will find the first focal plane, and that's where the FFP reticle is located. Inside the tube there are lenses that flip the image and if it's a variable riflescope, you will find a series of (usually 3) zoom lenses, that will focus the image onto what is referred to as the second focal plane. That is where the SFP reticle will be located if it's an SFP design. The erector tube is attached at the rear of the main tube in such a way as it can move up and down and sideways. The front of the tube is held in place by a combination of knobs and springs.

After the SFP and attached to te end of the main tube, you will find the eyepiece assembly, focused on the SFP or rear of the erector tube.

The erector tube in an inch (25.4mm) tube is the same diameter as the one in the 30mm tube, and the 34/35mm tube and the 40mm tube. It's about 19mm. The benefit of the larger diameter tubes is to provide more adjustment range for the erector tube, and/or provide for thicker walls for the main tube.

The reason I used weasel words at the start is that it's possible that a vendor will have a slightly larger erector tube because they have a larger ID in the main tube. My understanding is that these erector tube all have the same ID and use the same size lenses. Even is one vendor decided to have larger internal lenses, the increment in size would be minimal and would not have much benefit over the standard size. Also, changing the size of lenses has a lot of impact on the optical design. I can't imagine someone using a 20mm internal lens when erector tubes are all 19mm. Everything would have to be bigger and longer.

So, yeah, a larger tube would provide more light, if it weren't for that pesky erector tube.

Thanks for discussing it again. I couldn’t really follow everything in the Sniper’s Hide post I referenced, but it seemed to me that he wasn’t discussing light transmission only. In any event, it’s good to know that variations in the innards would be minimal at most, even assuming a manufacturer wanted to go to the trouble of adopting something different.

But to ensure I understand correctly, if someone decided to go with a larger diameter erector tube, that would work against the greater adjustment range benefit provided by a larger main tube, and for no significant optical benefit—yes?

And although you may have discussed all this eight years ago (and I admit I didn’t check), a lot can change in optics manufacturing practices, or I would at least assume so until advised otherwise.

Thanks again.

The following is conjecture at best.

Let's say we have a 40mm tube. One of the big benefits of such as tube is to make it thicker (more stable) and provide a wider range of adjustments. The downside is added weight and bulk.

In a 30mm tube, if the walls are 2mm thick, you will have an ID of 26mm. The usual erector tube is 19mm. So you have about 7mm of adjustment range. In a 34mm tube, you can have a thicker wall for added stability and protection as March and others do. The thickness goes from 2mm to 4mm and the ID remains the same as before at 26mm. Some decide to use the 34mm tube to extend the adjustment range another 4mm. I believe the 40mm scope does added thickness and more adjustment range, but I don't know that for sure.

You can easily look at the specs of various scopes and figure out what's what. Nightforce, March and a few others will definitely state they have thicker walls. March brags about it in the 34mm tubes. The adjustment range is the same as a 30mm scope, but it's much stronger and stable.

Now, let's say you use bigger internal lenses. Adding a few millimeters is not worth the amount of effort and cost you will have to put into the new optical design. So you will want to go at least 4-6mm larger. At that point, you will have something, but everything will have to scale up and the scope will be bigger, bulkier and much, much more expensive.

However, I am happy to be corrected.

So, my question then is what about a sunshade?
On a 50mm objective with one does it knock it down to say a 44mm without?

quote:

Originally posted by NikonUser:
fritz, I am sure, could have answered this.

Sometimes it's best to let those with more gooder answerz reply.

Seeees the light, he does...

quote:

Originally posted by sigmoid:
So, my question then is what about a sunshade?
On a 50mm objective with one does it knock it down to say a 44mm without?

The sunshade doesn't reduce the amount of light going to your eye. You have to remember that the objective lens forms its image at the first focal plane and the erector tube only looks at part of it and then the zoom lenses and the eyepice at the other end will further reduce the area being sampled.

I always have my sunshade on because it protects my objective lens and there have been cases where I have had to shoot in a direction that was very close to the setting Sun and the shade made sure I did not get any artifacts from the Sun in the lenses.

I do the same with my camera lenses.

I always have sunshades on my riflescopes, including a couple that I had to fabricate myself by gluing together adapter rings and other models’ shades because there were no factory shades available. One range where I sometimes shoot faces almost directly east and especially in the winter when the sun is low, a shade is essential in the morning when I usually shoot.

I suppose if you don’t need them, you don’t need them, but they are a given for me.

The most important thing in "light gathering" is the size of the exit pupil. This is the diameter of the shaft of light that hits your eye. It is determined by the size of the objective divided by the magnification. So a 50mm scope at 5x has a 10mm exit pupil and delivers the most light you can get to your eye. So can a 40mm scope at 4x. As you get a little older your eyes lose their ability to dialate to the full 10mm and decreases if you smoke too much etc. 8mm is probably a more useful maximum number and is why you used to see a lot of 7x56 scopes and binoculars for night hunting in Europe. Also if you are wobbling at all you won't be able to keep the full exit pupil on your Iris' and that why a lot of Marine binoculars aren't usually more than 7x. After twilight while you can still see. Look into a dark area at low magnification and zoom it. If it's dark enough it will black out at higher magnifications.

Another important thing is "Twilight Factor". quote: "The 'twilight factor' can be calculated by first multiplying the magnification by the objective lens diameter and then finding the square root of the result. For instance, the twilight factor of 8x42 binoculars is therefore the square root of 8x42: the square root of 336=18.3"

The larger the Twilight factor the more detail you can see at lower light. Basically more magnification of a given amount of light will let you see more, but to a point when your exit pupil cuts out.

As for Tube size and elevation, a larger tube CAN allow more elevation but it sometimes it doesn't if they use larger erector lenses etc. ALLWAYS check the amount of elevation on the EXACT scope you are buying, there are 30mm tube scopes out there that have LESS elevation than you are used to in 1" scopes. Check and know for sure!

And also Coatings, lens quality, your particular eyeballs etc. also make a big difference too.

In general make sure that you get a large enough objective for the way you hunt. If you like to hunt with a 6x fixed scope a 6x42 is all you ever need. But if you like to zoom it you'll probably want a larger objective. One of my best friends is one of the larger Swaro dealers in the country. In one particular model he sells the 50mm mag 15-1 over the 44mm model, because why have the higher magnification if you can't use it when you need to!

Anyway hope this makes a least a little bit of sense. Fortunately for us Scopes are much better than ever and there are LOTS of good choices. Just double check the amount of elevation and the weight (some nice scopes are heavy as hell!) of the particular scope you are interested in buying........