Date: Mon, 08 Apr 2002 07:44:27 From: "neil barnes" <[EMAIL PROTECTED]> Subject: Re: [LIB] [OT] RE: Digital cameras (danger Matt/Ray length exposition :)
>Date: Sat, 06 Apr 2002 08:24:31 +0000 >From: "Matthew Hanson" <[EMAIL PROTECTED]> >Subject: Re: [LIB] [OT] RE: Digital cameras (danger Matt/Ray length >exposition :) > >Aw shoot... Just when I thought I had David's explanation down, now I have >to get the broom and clean up these shattered pieces of comprehension I was >so confident with a few minutes ago. > >It made sense when David said: > > "Slow lens is a lens with a large aperture value when set > wide open (when the lens lets in as much light as it can), > eg. f/5.6.A fast lens is a lens with a small aperture value, > eg. f/1.8." > 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] >If the definition of a "slow lens" is as David describes, then I can see >where such a lens would be limited to slower shutter speeds when the lens >is >wide open, compared to the higher shutter speed capability of a wide open >lens with a f/1.8 aperture value. Yup. Bigger hole = more light = faster. > >And it made sense that if a lens is only capable of the highest aperture >value of 5.8 or greater, then I'd think that it WOULD in fact be limited to >the larger f/stops with higher depth of field. No? Not sure what you mean - if the largest aperture value is f5.6, then all other aperture values will have smaller holes, thus higher f-stop numbers, longer exposures, and greater depth of field. So yes. > > >>However, you must have good control of the focus to achieve this. Not what >>you want for point and click, and not what you want when you can't see a >>viewfinder image with the same resolutiuon as the final image.< >> >>Of course, one point I didn't mention - the depth of field is also >>proportional to the resolution of the image sensor - if that is low, then >>the depth of field is effectively increased, in that the image is equally >>soft either side of the focus point.< > >Let's see... if the image sensor resolution is low, then depth of field is >high. You getting this Raymond? 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. Neil _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com ************************************************************** 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 **************************************************************
