I often get scope questions and one that I get a lot but people can’t seem to wrap their head around, is if a scope with a larger tube lets in more light than a scope with a smaller tube. No, for all intensive purposes, larger tubes do not let in more light. What you do get with a larger diameter tube is more windage and elevation travel. The amount of light gathered and sent to your eye, the exit pupil, is determined by the objective lens and the power that you have your scope set on at any given time. A 6-24x50mm variable power scope, set on 10x with a objective of 50mm is going to have an exit pupil of 5. It’s simply the objective diameter divided by the power your scope is set on. If you increase the scopes magnification to 20x, the exit pupil is reduced to 2.5. That’s why when you change your scope from 27x to 8x or something like that, the scope looks super bright crisp and clear with a larger eye box. It’s also important to note that the maximum amount of light your eyes can take in is about 7. On a bright morning, when it’s clear outside, most scopes will look great. Very often, new shooters will get a recommendation for a mediocre scope that is priced very low. They buy it, mount it, take it outside to try it out in the middle of the day when the exit pupil is like 8 or 9 and it looks phenomenal. They rave about it and then either turn up the magnification or use it in the evening and all of a sudden it’s not very good. Plus, there is much, much more to a scope’s quality than the light gathering ability and clarity! Always compare optics, side by side in the early morning or late evening. That’s when the good and bad become much more evident! At twilight, having a scope with an exit pupil of 7 or greater will look phenomenal, the light to your eye, through the scope will be much more than your naked eye can gather. Sorry, I’m getting off track again. 
The reason I am writing this post is because today my son was asking me what’s inside of a rifle scope. I had an old scope that was cheap and didn’t ever work right, so today we took it apart so I could show my son the internal components. Like I said, it was a very cheap scope so there aren’t as many quality components inside as you would find in a Tier 1 scope. Looking at the pictures you will be able to see that regardless of the diameter of the tube, the light has to go through the erector which is very small in diameter compared to the 30mm tube it was housed inside of. That is what I wanted to point out in this post but I figured I’d share a little more since I’m posting anyway.
Because this scope was cheap, everything was pressed into place, there was epoxy everywhere and it was very hard to get apart. We scratched it up and bent it badly but the main components are still there to clearly see. From right to left, the objective lens group that gathers light, the erector that houses the reticle in a FFP scope on the first lens in the erector, nearest the objective(in the first focal plane), and SFP reticle on the last lens, nearest the eye piece(in the second focal plane). Also in the erector(in variable power scopes) are angled slots that move the erector or parts within it slightly forward or rearward to adjust magnification in variable power scopes. The turret screws interact with the side and top of the erector to move the reticle to the ideal position. When the screws are turned, releasing tension on the erector, there is a spring attached to the outside of the erector that pushes it back to it’s original position. This spring can take a “set” which is why it is best to use your scope with the reticle nearest the true, optical center. The main function of the erector however, is to “erect” the image, to turn it right side up before the image reaches the shooter’s eye. Last, we have the ocular assembly(the eye piece), where focusing the reticle takes place, and where the last two lenses in the scope are held.
There is obviously a whole lot more to a scopes construction, inner workings and explanations of how they work. Because I’m asked about the light gathering capabilities between a 1”, 30mm and 34mm scope a lot, I just wanted to share the pictures of the erector’s diameter and the lenses since we took apart this scope. We just thought it was kind of cool. Although not many people really think about it, rifle scopes are a pretty complex piece of engineering. These scopes are often subjected to heavy recoil, multi-directional recoil, falls, possible tube damage caused by over tightening rings, possible water intrusion, etc, etc. If the scope’s lenses are not perfectly ground, polished and coated, the other components machined to exacting tolerances and if it isn’t perfectly assembled, purged, components epoxied in place when necessary, there will either be problems, it will fail or it will not hold zero! Even one of the lenses, not being absolutely, perfectly aligned with any of the other corresponding lenses, will cause the exit pupil to be off or something even more serious. There is just so much to these scopes and everything has to be right. The old adage, “you get what you pay for” usually holds true with optics! Of course, there are some great deals out there and new companies selling superb optics for a great price, like Arken, but generally, you’re not going to pay $300 and get the performance of a $1000 optic.
Quality optics are expensive because they are either made in Europe or Japan(LOW is one of, if not the best), they use the best optical glass(Schott), the grinds are flawless, they use coatings on all lens surfaces, not just the lenses exposed to air or just the objective lens, they use quality materials internally(Brass or stainless) vs. plastic, the scopes are purged with expensive gasses like Nitrogen or Argon, quality testing and quality control are more thorough and the warranty is usually 10-20 years or lifetime. Don’t let a 10-20 year warranty scare you either. Most scopes fail within the first year and will be repaired or replaced. Last, higher priced scopes come with far more extras…Zero stop, side focus, better turrets, smoother eye piece, exposed, lockable turrets, a close focus distance, lens shade, parallax wheel, etc… I’m rambling again!
Whoa, this post ended up being a lot longer than I ever intended. Sorry!
Have a great evening.
Stoti
Scopes internals as described above. The objective is on the right, the erector middle. This is a SFP scope the reticle is in the large part of the erector on the left end and the turret knobs are placed above and beside where they would interact with the erector, the eye piece and lens are far left.
The reason I am writing this post is because today my son was asking me what’s inside of a rifle scope. I had an old scope that was cheap and didn’t ever work right, so today we took it apart so I could show my son the internal components. Like I said, it was a very cheap scope so there aren’t as many quality components inside as you would find in a Tier 1 scope. Looking at the pictures you will be able to see that regardless of the diameter of the tube, the light has to go through the erector which is very small in diameter compared to the 30mm tube it was housed inside of. That is what I wanted to point out in this post but I figured I’d share a little more since I’m posting anyway.
Because this scope was cheap, everything was pressed into place, there was epoxy everywhere and it was very hard to get apart. We scratched it up and bent it badly but the main components are still there to clearly see. From right to left, the objective lens group that gathers light, the erector that houses the reticle in a FFP scope on the first lens in the erector, nearest the objective(in the first focal plane), and SFP reticle on the last lens, nearest the eye piece(in the second focal plane). Also in the erector(in variable power scopes) are angled slots that move the erector or parts within it slightly forward or rearward to adjust magnification in variable power scopes. The turret screws interact with the side and top of the erector to move the reticle to the ideal position. When the screws are turned, releasing tension on the erector, there is a spring attached to the outside of the erector that pushes it back to it’s original position. This spring can take a “set” which is why it is best to use your scope with the reticle nearest the true, optical center. The main function of the erector however, is to “erect” the image, to turn it right side up before the image reaches the shooter’s eye. Last, we have the ocular assembly(the eye piece), where focusing the reticle takes place, and where the last two lenses in the scope are held.
There is obviously a whole lot more to a scopes construction, inner workings and explanations of how they work. Because I’m asked about the light gathering capabilities between a 1”, 30mm and 34mm scope a lot, I just wanted to share the pictures of the erector’s diameter and the lenses since we took apart this scope. We just thought it was kind of cool. Although not many people really think about it, rifle scopes are a pretty complex piece of engineering. These scopes are often subjected to heavy recoil, multi-directional recoil, falls, possible tube damage caused by over tightening rings, possible water intrusion, etc, etc. If the scope’s lenses are not perfectly ground, polished and coated, the other components machined to exacting tolerances and if it isn’t perfectly assembled, purged, components epoxied in place when necessary, there will either be problems, it will fail or it will not hold zero! Even one of the lenses, not being absolutely, perfectly aligned with any of the other corresponding lenses, will cause the exit pupil to be off or something even more serious. There is just so much to these scopes and everything has to be right. The old adage, “you get what you pay for” usually holds true with optics! Of course, there are some great deals out there and new companies selling superb optics for a great price, like Arken, but generally, you’re not going to pay $300 and get the performance of a $1000 optic.
Quality optics are expensive because they are either made in Europe or Japan(LOW is one of, if not the best), they use the best optical glass(Schott), the grinds are flawless, they use coatings on all lens surfaces, not just the lenses exposed to air or just the objective lens, they use quality materials internally(Brass or stainless) vs. plastic, the scopes are purged with expensive gasses like Nitrogen or Argon, quality testing and quality control are more thorough and the warranty is usually 10-20 years or lifetime. Don’t let a 10-20 year warranty scare you either. Most scopes fail within the first year and will be repaired or replaced. Last, higher priced scopes come with far more extras…Zero stop, side focus, better turrets, smoother eye piece, exposed, lockable turrets, a close focus distance, lens shade, parallax wheel, etc… I’m rambling again!
Whoa, this post ended up being a lot longer than I ever intended. Sorry!
Have a great evening.
Stoti
Scopes internals as described above. The objective is on the right, the erector middle. This is a SFP scope the reticle is in the large part of the erector on the left end and the turret knobs are placed above and beside where they would interact with the erector, the eye piece and lens are far left.
