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From: kr@ken.UUCP (Ken Robinson)
Newsgroups: rec.audio,sci.electronics,rec.aviation
Subject: Re: Noise-cancelling microphone
Message-ID: <429@rlvd.UUCP>
Date: Mon, 1-Jun-87 04:40:23 EDT
Article-I.D.: rlvd.429
Posted: Mon Jun  1 04:40:23 1987
Date-Received: Sat, 6-Jun-87 10:27:40 EDT
References: <19549@sun.uucp> <1027@mips.UUCP> <689@cod.UUCP> <867@lll-lcc.aRpA> <2849@mit-hermes.AI.MIT.EDU> <2780@pucc.Princeton.EDU>
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Reply-To: kr@uk.ac.rl.vd (Ken Robinson)
Organization: Informatics Division, R.A.L
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Xref: mnetor rec.audio:1827 sci.electronics:782 rec.aviation:1814

In article <2780@pucc.Princeton.EDU> 6062871@pucc.Princeton.EDU writes:
>
>In article <19549@sun.uucp>, brent%terra@Sun.COM (Brent Callaghan) writes:
> 
>>I remember some years ago reading a similar article in
>>New Scientist about an optical element that had just been
>>invented for large telescopes that corrected images that
>>lay at the extremes of the telescopes' field.... The human
>>eye can resolve detail sharply over a small area at the
>>center of the visual field.  The new element would correct
>>off-axis images so that the high visual acuity would extend
>>over the whole visual field.  The amount of eye movement
> 
>I'm skeptical because, recalling my high-school biology, the human
>eye's resolution is best for images that are focused on the fovea,
>a small circle at the center of the retina that has a high density
>of light-sensitive (and color-sensitive) cone cells. This is the
>area that permits me to see what I am typing. Outside of this area,
>the density is lower, so the device won't do much good.> 

In fact large astronomical telescopes are used to record on *film*,
so that your comment on the small angular field of view of the eye,
while true, is not relevant.  Schmidt telescopes do indeed have a 
correcting lens before a spherical mirror.  This gives good accuracy
over a very wide field of view.

Ken Robinson                                     kr@uk.ac.rl.vd
Informatics Division
Rutherford Appleton Laboratory
Chilton
Didcot Oxon OX11 0QX