Path: utzoo!attcan!utgpu!watserv1!watcgl!imax!dave From: dave@imax.com (Dave Martindale) Newsgroups: comp.graphics Subject: Re: digitizing images (was Re: Scientific Visualization again) Keywords: digitizing CD Message-ID: <1989Nov30.172716.738@imax.com> Date: 30 Nov 89 17:27:16 GMT References: <11726@phoenix.Princeton.EDU> <1989Nov25.142552.1702@hellgate.utah.edu> <3399@jhunix.HCF.JHU.EDU> <5646@eos.UUCP> <1989Nov27.024857.9480@ux1.cso.uiuc.edu> <126@tobler.UUCP> Reply-To: dave@imax.com (Dave Martindale) Organization: Imax Systems Corporation, Oakville Ontario Lines: 30 In article <126@tobler.UUCP> iony@tobler.UUCP (Ion Yadigaroglu) writes: > > This discussion brings to mind a project I've had for some time > (not in any way started). I was thinking of modifying a CD player > to make a microdensitometer. You would put the (small) strip > of film on a disk with a big hole cut out. Advantage would be > of course that you could re-use most of the CD player, including > laser, lens, motor, speed-controling circuit, stepper motor > for laser, and maybe even the feedback tracking circuit (to > position the laser). The only hardware missing is a good > intensity cell on the other side with its A/D converter. Well, it's not this simple. A CD player has a 2-axis positioning system (tracking and focus) that is specially designed to follow a spiral pattern of pits on a disc. All of the signals that drive the focus and tracking servos come from that spiral track of data. If you replace the very specific pattern of the CD data surface with an arbitrary piece of film, these servo circuits could not function. You'd have to replace the focus and tracking circuitry with something that can do high-accuracy positioning using its own references, instead of following a pre-written pattern. You could use a laser interferometer or similar system to provide the position feedback for the laser head. But it would likely be far cheaper to scrap the entire CD positioning system and use precision mechanical screws instead. The laser block out of a discarded CD player might be useful though. Brought to you by Super Global Mega Corp .com