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From: ken@sugra.uucp (Kenneth Ng)
Newsgroups: sci.electronics
Subject: Re: Those little autofocus cameras
Message-ID: <1991Jun17.020708.2493@sugra.uucp>
Date: 17 Jun 91 02:07:08 GMT
References: <1991Jun8.020128.23216@milton.u.washington.edu> <1990029@hpldsla.sid.hp.com>
Organization: Private computer - Bloomfield NJ USA
Lines: 31

In article <1990029@hpldsla.sid.hp.com>, tonya@hpldsla.sid.hp.com (Tony Arnerich) writes:
: They work through triangulation, just like the rangefinder cameras of
: the 60's.
: In no case does any imaging take place in the point&shoot's focus innards.
: tonya@sid.hp.com

I have a Minolta Maxxum 7000 and I'm quite sure it does not use rangefinder
technology.  From much experimentation I have deduced that it works by
maximumizing the contrast between adjacent elements.  And apparently
the elements it helps the contrast with are horizontal because it works
best with vertical contrast (ala buildings as opposed to venician blinds).
Modern/Popular Photography had an article on exactly how it worked once,
but I didn't quite understand all of it.

better

: One lens projects a thin vertical stripe of IR onto the subject. The
: other images onto either a scanning mirror (hooked up to the focus
: mechanism - this is exactly how the old RF cameras worked), or a diode
: array. Explanation #2 is just speculation, inspired by the high production
: volume of diode arrays for AF SLR's.

I did see one example of a LED diode array, it was in the NASA Tech Briefs,
an example on a rangefinder with no moving parts.  It had an LED array with
each LED pointed in a slightly different angle.  BTW: NASA Tech Briefs is
an *EXCELLENT* rag for seeing what can be done with technology.

-- 
Kenneth Ng
Please reply to ken@hertz.njit.edu until this machine properly recieves mail.
"No problem, here's how you build it" -- R. Barclay, ST: TNG