I think I answered a lot of this in my post to Spawn. Again, is it easier to create a good optical system in a 34 vs. 30?...it depends on what a person defines as "good". If it HAS to have 33 mils of travel to be considered good then the answer is yes. However, I can just as easily give the same MTF, CA, spherical aberration, coma, astigmatism, etc. in a 30mm tube system (and smaller diameter erector asembly) as a 34mm tube system.. The mechanical designer will most likely just give less travel to the entire system and that will be the difference. I think most of these tactical scopes are always 34mm because they are trying to achieve BOTH 30+ mils of travel, large FOV, and good optical quality. But it's really the FOV and travel that is driving it, not the "optical quality" part...(or what I define as "optical quality" meaning MTF, CA, and the other aberrations)



Here's a cool fact. Take a FFP rifle scope. The reticle in a FFP scope sits under your turrets. How big is 1 Mil on the actual reticle? In other words, if you took the glass reticle out of your scope and put it under a microscope, how far apart would the lines physically be at a 1 mil interval? Since a mil is an angular unit we have to convert a linear unit to an angular Mil based on the optical system. And it depends on the objective focal length. So, I'll make up a plausible focal length for a long range scope of 150mm. Take 150mm divided by 1000 which gives you 0.15mm. So, on a glass reticle in a 150mm focal length scope a 1 mil increment on the reticle will (hopefully) be made to exactly 0.15mm apart. Every single scope has a slightly different focal length and it's usually not a perfect round number like 150mm. It might actually be 150.234, for example. This is actually why a lot of guys say "you made X reticle for Y scope, can't you just put that reticle in your Z scope?". Well, no, because they have very different front focal lengths. They also have different glass reticle outside diameters, and a few other different dimensions too. So the pattern may look the same and subtend the same in two different scopes but the physical reticle itself is different and requires a whole new design and tooling.



So, knowing that, the reticle sits on the end of your erector tube and the erector tube (and hence reticle) moves around by being pushed by the turret screws. If the reticle moves 0.15mm in the above scenario...guess what? You just moved your reticle 1 Mil, which means you would have just dialed 1 Mil on your turret, which means the thread pitch of the turret is really important to match all of this. AND, you can see that if you have a bigger tube you have more room to move, and therefore more travel. In fact the erector unit may, or may not be the same size as a smaller tube scope...it really has no bearing on light transmission since light is compressible...you just have more room to move and therefore more travel. Also, you can see FOV is tied to this, right? FOV is an angular measurement. So, more diameter means more room for the designer to design a bigger reticle (and therefore bigger erector assembly) and if you meld that with the proper optical design and ray traces this means a bigger FOV...oh, wait! Except if you make the reticle bigger you just reduced room for more travel!! So, you can see that FOV and travel fight one another and so you need to find an optimum balance between the two.

Now, if you have a requirement for 33 mils of travel and absolutely no less...AND you want a really good optical system, then a bigger tube is definitely going to make it easier, which I think is obvious. In a smaller tube the only other way to achieve it would be to have a shorter focal length hence shorter physical distance to achieve 1 mil of travel, hence less room required (and shorter focal lengths are usually harder to optimize for)...so, bingo! Here is a case where a larger tube would be easier to optimize for. Usually, however, a smaller tube design will just slash some of the travel to keep a more manageable focal length, which then makes it just as easy to achieve just as good of an optical system. So, if a 30mm tube gives you all the travel you need, and ample FOV, rest assured the designer gave it just as good, or maybe even better, "optical quality" as a 34mm tube...it just likely has less travel and maybe slightly less FOV than a 34mm equivalent scope. The "optical quality" part really comes down the design and a good optical designer using a great CAD optical design system with a lot of knowledge about optics to make the computer system work well for you, good grinding, polishing and coating, and great assembly techniques for precisely lining everything up to the computer theoretical model.



Oh, and get this. So, most scopes travel in 0.1 mil increments. So that means in a 150mm scope the reticle and turret screw travel 0.015mm. A human hair is about 0.080mm in diameter. So, 0.1 mil of travel in this scope means a movement about one fifth of one human hair. So, all these tracking tests (thank you Killswitch! You da man holding peoples feet to the fire! means we have our work cut out for us. If you turn your knob 10 mils and are off 0.1mil, that means you have a 1% error...which means you have a turret travel error of 0.015mm...that's 15 MICRONS of error over 10 mils (almost half a "thou" for you English machinists out there)!!<---sorry late night math...had to fix that one...and we are doing it!! And we love the challenge too

Now, I didn't really even get into first order optics at all. Just trying to keep this all in layman's terms plus I don't want to cross the line into the proprietary. Hope that was fun and informative. With that I'm off to bed. Thanks all!