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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12513
Loc: Cumberland, R I , USA42N71.4W
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Re: William Optics 7x50 ED binocular minireview
11/20/05 06:33 PM
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Hi Pier,
your English is fine, no need to apologize anymore. We know you now.
Early tonight I re-checked the sharpness across the field. I mounted the binocular on a slo-motion head and observed nu Draco, taking notes.
Nu Draco is 62 arcseconds. That gives 434 arcsec apparent resolution.
visible out to 95%/100% to the right, towards the 3 o'clock position.
visible to 90% towards top, distorted further out.
visible to 80-85% towards bottom, distorted further out.
visible only to 70-75% towards left, distorted further out.
Stars begin to spread out like arcs.
This would indicate the sharpest point in the field is shifted about 1° off-center approximately towards the 2 oclock position.
There is no major difference in the field overlap when focused at infinity. This was noticed yesterday in daylight when focused at 200 feet. This must be seen in daylight as parallax when observing close objects. On stars, with nu Draco at the edge, I measured overlap within 2 arcminutes. That's negligible. In daylight I measured 1 foot in 200 feet or 15 arcminutes, a very noticable field error.
Stars are merged to within less than 1 arcmin.
edz
--------------------
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