Date: Mon, 08 Apr 2002 21:03:21 +0800 From: Raymond <[EMAIL PROTECTED]> Subject: Re: [LIB] [OT] RE: Digital cameras (danger Matt/Ray length exposition :)
Grr ... I should read my emails backwards so I don't end up posting similar responses to what others have already posted ... >Yup. But note the difference between 'aperture value' and 'aperture'. >Aperture value is focal distance of lens divided by width of hole through >middle (with fudge factors for modern zoom type optics) so the smaller the >hole, the bigger the aperture value = f-stop. >[for the curious, I still have a lens somewhere around where the f-stop is >an actual strip of brass with a series of different sized holes in it] Actually, I swear my digital camera doesn't even HAVE an expanding/contracting 'iris' and instead has a thin piece of metal with a few different sized holes in it and a solenoid that switches the holes in and out .... I guess for something that doesn't need to be continuously variable (because in between stops the CCD sensitivity can be adjusted to compensate) its probably cheaper and more reliable than an iris system ... >Yes, because depth of field is to do with the number of lines of >resolution in the final image, and how far either side of the focus point >they can be resolved. If your image sensor resolution is low, then you >can't actually see the higher resolution in the centre of the focus range >- you might consider it an enhanced depth of constant fuzziness. I don't >know if domestic electronic cameras do this, but all professional CCD tv >cameras use an optical low pass filter (i.e a carefully etched bit of >frosted glass) to prevent aliasing of un-resolvable image information. Are you *sure* its being used as an optical low pass filter? It does seem a little pointless given that you're not performing perfect sampling with a CCD anyway (plus you'd think you would get enough charge leakage to perform your pre-sampling low-pass filtering anyway). All the CCD cameras I've seen DO have a filter in front of the lens but its more an IR filter with a substantial anti-reflective coating on it ... - Raymond --- /~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\ | | "Does fuzzy logic tickle?" | | ___ | "My HDD has no reverse. How do I backup?" | | /__/ +-------------------------------------------| | / \ a y b o t | [EMAIL PROTECTED] | | | HTTP://www.raybot.net | | ICQ: 31756092 | Need help? Visit #Windows98 on DALNet! | \~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~/ ************************************************************** http://libretto.basiclink.com - Libretto mailing list http://www.silverace.com/libretto/ - Archives -------TO UNSUBSCRIBE------- Reply to any of the list messages. The reply mail should be addressed to: [EMAIL PROTECTED] - Then replace any text on the message's subject line: cmd:unsubscribe --------TO UNSUBSCRIBE DIGEST------ Do above but with this on subject line: cmd:unsubscribe digest **************************************************************
