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Posted: 1/27/2007 2:52:37 PM EDT
| Anyone know the MOA subtension of the larger 0-200 aperture? |
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I tried to look it up but i can't find it. Subtension = span, i.e., does the aperture span 100 MOA edge-to-edge, 125 MOA, etc. Reason I ask is I'm curious about Leupold's Prismatic sight. They designed the outer ring to span 184 MOA. Why, I don't know and I'm just trying to compare some other "known quantity" aperture sizes to see if I can find a correlation. Their CQT spans around 212 MOA at 1x. That's really driven by their 2nd focal plane design and the fact that they designed the reticle to subtend right around 70 MOA (approx 6ft) at the 3x setting. This allows it to serve as a quasi-range finding feature. Makes sense when you are ranging a human standing upright. When you dial back down to 1x, you end up with about 212 MOA subtension. That doesn't make a lot of sense for CQB. Given their new Prismatic is 1x, it seems it's designed to serve better in the CQB role, so it would make sense to pick a reticle subtension much less than 212 MOA. The EoTech reticle spans 65 MOA. It's pretty universally recognized as being a good CQB optic. The Prismatic is 184. Things that make you go hmm....... Then I got to wondering if the 184 equated to the subtension of the large 0-200 aperture on the rear sight. Using my Eotech as a rough guide, I'm guessing just slightly less than two Eotech reticles side-by-side would span the aperture, that's when I'm using a NTCH hold. I'm guessing around 115 MOA subtension, but that's a guess. I could see the rationale if Leupold sized their aperture ring to coincide with the large 0-200 aperture. But if my rough calculations are close, the Prismatic's ring is probably half as big as the current 0-200 aperture, and I'm trying to figure out if that makes sense. As it stands their 184 aperture would span a typical body width out to around 10 yards. Beyond that the ring is larger than the torso. I guess I'm wondering why they didn't go smaller given they changed it from their CQT reticle -- I just wonder what their design rationale was. I guess I'll just have to get to see one in the flesh before I pass judgement, but the idea of a battery-free 1x optic makes a lot of sense to me. Intuitively, I just wish they would have downsized that ring a bit more than they did. |
| I don't think there is an answer to your question. The closer your eye is to the opening on the sight, the wider an area it will span. The farther away your eye is, the narrower your span is. This is because your field of view is essentially formed by a cone which has its point at your eye, and its circumference defined by the sight. If you are closer, that circumference is closer to your eye, so althought the circumference is the same, the cone will spread out larger. |
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Here's how to get a quick and dirty number. Anyone spots any errors, please correct me. If D is the diameter of the aperture, and r is the distance from your eye to the aperture: MOA = (D/r)*3437 Here's how to work it out: You need: - Aperture diameter (I think it's 0.200" for the A2 large aperture, but I could be wrong). - Distance from your eye to the aperture. To be precise, you'd want the distance from the back of your eye to the aperture, but be careful with that ruler! The distance from your eye to the aperture defines the radius of the circle with your eye at the center that the aperture is a part of. To find the diameter of that circle, use 2*pi*radius. I'll pick 5" from eye to sight, which will give us 2*3.14*5, or 31.42". If the A2 radius is 0.2", then its portion of that radius is (a2 radius)/(circle diameter), or 0.2/31.42, or .0064 (0.64%) of the total. A circle is 360 degrees, and a degree is 60 minutes of angle (MOA), so a circle is 360*60 = 21,600 minutes. The sight aperture is 0.64% of this 21,600 minutes, or 0.0064*21,600 = 138.2 MOA, or about 2.3 degrees. This will obviously change as you move your eye closer or further from the aperture. To plug in your own numbers, you can use this: (D/(2*pi*r))*21,600, where D is the diameter of the aperture and r is the distance from eye to sight. This simplifies to (D/r)*3437, which is close enough for government work. |
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