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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
Adjusting reticle vs. Adjusting mounting - Burris Zee rings
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<blockquote data-quote="bruce_ventura" data-source="post: 701281" data-attributes="member: 34084"><p>It's really a matter of degree (pun intended). It sounds like trebark is looking for a technical or at least plausible explanation, so here it is. </p><p></p><p>The objective lens on most scopes is a simple doublet achromatic design. This type of lens exhibits optical aberrations as the incidence angle of the light increases (i.e., as the viewing angle increases). As this angle increases, various aberrations, such as spherical, coma, field curvature, and off-axis chroma, will blur the image. Other aberrations, such as barrel or pincushion distortion, will cause the image to contract or expand. These effects become worse as the incidence angle increases. So, yes the image is clearer and the adjustments are more accurate near the center of the field of view. </p><p></p><p>For most scopes, the aberrations in the erector lenses are more noticeable than those in the objective. The erector aberrations are observed as you look from center to the edge of the field of view. The aberrations in the objective are difficult to "see" because the manifest themselves only as the elevation/windage knobs are rotated large amounts. </p><p></p><p>The first aberrations you will likely notice are field curvature and field distortion. Field curvature is a change in focus and can be removed by adjusting the AO or SF knobs. Field curvature causes an error in the adjustment at large viewing angles. </p><p></p><p>For viewing angles up to about 15 MOA, I have not been able to detect these aberrations visually on any but very cheap scopes. For viewing angles of 15-30 MOA (one-quarter to one-half a degree) the aberrations start to become visible to the trained eye. Above 30 MOA the aberrations become more obvious. At these angles image blurring occurs that cannot be corrected with the AO or SF knobs. </p><p></p><p>So, I recommend getting the scope tube axis aligned with the rifle bore axis to within +/- 15 MOA. This can be done with Burris Signature rings, or by using shims and windage adjustable bases. I also recommend using biased bases (or Signature rings) on long range rifles to minimize the elevation adjustment for long range shots. </p><p></p><p>FYI, in about a week HighPowerOptics will start renting rifle scope installation kits that allow you to align the scope to the rifle bore in this way.</p></blockquote><p></p>
[QUOTE="bruce_ventura, post: 701281, member: 34084"] It's really a matter of degree (pun intended). It sounds like trebark is looking for a technical or at least plausible explanation, so here it is. The objective lens on most scopes is a simple doublet achromatic design. This type of lens exhibits optical aberrations as the incidence angle of the light increases (i.e., as the viewing angle increases). As this angle increases, various aberrations, such as spherical, coma, field curvature, and off-axis chroma, will blur the image. Other aberrations, such as barrel or pincushion distortion, will cause the image to contract or expand. These effects become worse as the incidence angle increases. So, yes the image is clearer and the adjustments are more accurate near the center of the field of view. For most scopes, the aberrations in the erector lenses are more noticeable than those in the objective. The erector aberrations are observed as you look from center to the edge of the field of view. The aberrations in the objective are difficult to "see" because the manifest themselves only as the elevation/windage knobs are rotated large amounts. The first aberrations you will likely notice are field curvature and field distortion. Field curvature is a change in focus and can be removed by adjusting the AO or SF knobs. Field curvature causes an error in the adjustment at large viewing angles. For viewing angles up to about 15 MOA, I have not been able to detect these aberrations visually on any but very cheap scopes. For viewing angles of 15-30 MOA (one-quarter to one-half a degree) the aberrations start to become visible to the trained eye. Above 30 MOA the aberrations become more obvious. At these angles image blurring occurs that cannot be corrected with the AO or SF knobs. So, I recommend getting the scope tube axis aligned with the rifle bore axis to within +/- 15 MOA. This can be done with Burris Signature rings, or by using shims and windage adjustable bases. I also recommend using biased bases (or Signature rings) on long range rifles to minimize the elevation adjustment for long range shots. FYI, in about a week HighPowerOptics will start renting rifle scope installation kits that allow you to align the scope to the rifle bore in this way. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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Adjusting reticle vs. Adjusting mounting - Burris Zee rings
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