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Checked field sharpness. Aprox measures - 60 arcsec seen out to 75% of field, about 120 arcsec total aberration at 100%. About equal with the Oberwerk Mariner. Better than all the other 7x50s except for the Prostar (which is on the order of 4x-5x better).

At 70% out about half to 2/3rds of aberration is curvature. At 100% about half to 40% is curvature. At edge seems like mostly astigmatism, but compared to all others is well controlled. Overall, I'd say field sharpness rates very well.

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Hmmm, checked field sharpness again last night. this time with specific placement measures.

Actual TFOV was measured at 7.1°, equals specified fov.

Has 60 arcseconds of total distortion between 65%-70% out from center. Has about 100 arcseconds distortions at about 90% out and no more than 120 arcsec at 100% out. At 50% out distortion is negligable. I'd estimate it at 10-15 arcseconds.

So within the central 50-55%%, the correction is excellent. At 65% out it begins to approach the average correction of most other good-better binoculars, but not the best. By 80-90% out it is average.

The amount of curvature measured at 70% out was half of the total distortion. So curvature is responsible for approx 30 out of 60 arcseconds distortion at 70% out. By 90% out most of the distortion was caused by other than curvature, seems like mostly astigmatism, and could not be focused out.

Net sharp fov for detail (to 1 arcmin distortion) is 5.0°. Net usable fov could be considered wider for scanning, perhaps 6.0°.

edz


edz

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