Now, the next BIG contest is ON!
in [Digital Cameras]
|
Prev: Here Comes the 3-D Camera: Revolutionary Prototype Films Worldin Three Dimensions
Next: Why the Nikon Coolscan V ED is so expensive event on vintage market ?
From: J. Clarke on 19 May 2010 07:37 On 5/19/2010 5:38 AM, DanP wrote: > On May 18, 6:21 pm, rfisc...(a)sonic.net (Ray Fischer) wrote: >> DanP<dan.pe...(a)hotmail.com> wrote: >>> To close the subject, after some reading and thinking lens diameter >>> does not affect the amount of light captured. >>> But a smaller lens needs to be polished more precise than a big one to >>> have the same IQ. >>> In real life better quality lenses have a bigger diameter. >> >> When lenses are (effectively) perfect the only way to improve >> resolution is to increase the aperture diameter. >> >> -- >> Ray Fischer >> rfisc...(a)sonic.net > > Say you have a f/2 50mm prime lens with an outside lens diameter of > 32mm and another one with a diameter of 72mm and for the sake of the > argument both perfect. > > The 72mm can have a lower f number but if both set at f/2 it will > produce identical results as both will let in the same ammount of > light. The results will not necessarily be identical. The 72mm is still passing light from all parts of the 72mm circle to the sensor, even when stopped down to f/2, however there will be filtering of the paths taken and some other effects. > This is because although both are set to f/2 the aperture size > measured in inch/mm is smaller on the 72mm lens. Why would it be smaller on the 72mm than on the 32mm? > If you want to set the exposure time manualy on an old film camera you > will read a light meter, consider the film ISO and the lens aperture > (f number). > So the size of the lenses is irrelevant. > > Am I missing something? > > > DanP
From: whisky-dave on 19 May 2010 08:55 "Wolfgang Weisselberg" <ozcvgtt02(a)sneakemail.com> wrote in message news:nlf8c7-faj.ln1(a)ID-52418.user.berlin.de... > DanP <dan.petre(a)hotmail.com> wrote: > >> To close the subject, after some reading and thinking lens diameter >> does not affect the amount of light captured. > > But it does. Take a distant star --- all lightrays are for all > purposes of a lens or telescope completely parallel here on Earth. > Obviously a larger lens diameter means a larger area and thus more > rays i.e. more light is captured. (I understand that's one of > the reasons Canon's 200mm f/1.8 are popular for some computerized > skywatching tasks: comparatively large front lens at a manageable > pricepoint.) http://en.wikipedia.org/wiki/F-number >> But a smaller lens needs to be polished more precise than a big one to >> have the same IQ. > > ... since a smaller sensor needs more enlargement. > >> In real life better quality lenses have a bigger diameter. > > In real life better quality lenses are faster, too. Is that true, I'm sure I have had lenes were this didn;t make any sense. I remmebr whne peole tested lens and the faster the lens didn;t make it better quaility, the quaslity was dependent on the manufacturing technigues rather than the size of the glass element.
From: Allen on 19 May 2010 09:42 whisky-dave wrote: > "Wolfgang Weisselberg" <ozcvgtt02(a)sneakemail.com> wrote in message > news:nlf8c7-faj.ln1(a)ID-52418.user.berlin.de... >> DanP <dan.petre(a)hotmail.com> wrote: >> >>> To close the subject, after some reading and thinking lens diameter >>> does not affect the amount of light captured. >> But it does. Take a distant star --- all lightrays are for all >> purposes of a lens or telescope completely parallel here on Earth. >> Obviously a larger lens diameter means a larger area and thus more >> rays i.e. more light is captured. (I understand that's one of >> the reasons Canon's 200mm f/1.8 are popular for some computerized >> skywatching tasks: comparatively large front lens at a manageable >> pricepoint.) > > http://en.wikipedia.org/wiki/F-number > > >>> But a smaller lens needs to be polished more precise than a big one to >>> have the same IQ. >> ... since a smaller sensor needs more enlargement. >> >>> In real life better quality lenses have a bigger diameter. >> In real life better quality lenses are faster, too. > > Is that true, I'm sure I have had lenes were this didn;t make any sense. > I remmebr whne peole tested lens and the faster the lens didn;t make > it better quaility, the quaslity was dependent on the manufacturing > technigues > rather than the size of the glass element. > > The whisky is showing in your post. Don't you have a spellcheck program? Allen
From: DanP on 19 May 2010 09:47 On May 19, 12:37 pm, "J. Clarke" <jclarke.use...(a)cox.net> wrote: > On 5/19/2010 5:38 AM, DanP wrote: > > This is because although both are set to f/2 the aperture size > > measured in inch/mm is smaller on the 72mm lens. > > Why would it be smaller on the 72mm than on the 32mm? The same f number has to let in the same ammount of light, so bigger surface captures more light, smaller aperture (measuren in inch/mm) makes it right again. Just remember the old days when exposure time used to be established by the light meter, ISO and aperture f number. And it worked for any combination of film (same ISO number), cameras and lenses. Being a bigger size the light is scattered more by the big lenses because of the longer light path and thus smaller aperture (measured in inch/mm) is required to have the same DOF. DanP
From: Ray Fischer on 22 May 2010 16:21
DanP <dan.petre(a)hotmail.com> wrote: >On May 18, 6:21�pm, rfisc...(a)sonic.net (Ray Fischer) wrote: >> DanP �<dan.pe...(a)hotmail.com> wrote: >> >To close the subject, after some reading and thinking lens diameter >> >does not affect the amount of light captured. >> >But a smaller lens needs to be polished more precise than a big one to >> >have the same IQ. >> >In real life better quality lenses have a bigger diameter. >> >> When lenses are (effectively) perfect the only way to improve >> resolution is to increase the aperture diameter. > >Say you have a f/2 50mm prime lens with an outside lens diameter of >32mm and another one with a diameter of 72mm and for the sake of the >argument both perfect. > >The 72mm can have a lower f number but if both set at f/2 it will >produce identical results as both will let in the same ammount of >light. I referred to resolution. Are you having difficulty following along? And "aperture diameter" refers to the size of the primary element. It does not refer to "aperture" or f-stop. -- Ray Fischer rfischer(a)sonic.net |