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From: Wolfgang Weisselberg on 5 Jun 2010 08:20 whisky-dave <whisky-dave(a)final.front.ear> wrote: > "Wolfgang Weisselberg" <ozcvgtt02(a)sneakemail.com> wrote in message >> whisky-dave <whisky-dave(a)final.front.ear> wrote: >>> No one heard of gravitational lensing ? >> Sure, but Earth's diameter is too small to detect any differences from >> parallel rays. > But trh sun isn't. You can't see the stars during the day anyway. >> You need Earth's orbit as a baseline to detect differences >> for close stars. > But the problem is how to you get two exactly parallel 'rays'. The solution is infinitely far away objects. Stars are sufficiently far away for any single telescope. -Wolfgang
From: George Kerby on 5 Jun 2010 14:07 On 6/5/10 7:20 AM, in article 62spd7-tk3.ln1(a)ID-52418.user.berlin.de, "Wolfgang Weisselberg" <ozcvgtt02(a)sneakemail.com> wrote: > whisky-dave <whisky-dave(a)final.front.ear> wrote: >> "Wolfgang Weisselberg" <ozcvgtt02(a)sneakemail.com> wrote in message >>> whisky-dave <whisky-dave(a)final.front.ear> wrote: > >>>> No one heard of gravitational lensing ? > >>> Sure, but Earth's diameter is too small to detect any differences from >>> parallel rays. > >> But trh sun isn't. > > You can't see the stars during the day anyway. > Almost right: Only one.
From: DanP on 5 Jun 2010 17:35 > I guess you could do a thought experiment. > If 2 lenses gather the same amount of parallel rays along > their lens axis, they must have the same diameter. Go from > there. Right, at maximum lens aperture bigger lenses gather more light. Close the bigger lenses aperture to match the small ones and you get the same amount of light. DanP
From: whisky-dave on 7 Jun 2010 08:28 "Martin Brown" <|||newspam|||@nezumi.demon.co.uk> wrote in message news:HS6On.18516$%u7.7097(a)newsfe14.iad... > On 04/06/2010 13:46, whisky-dave wrote: >> "Wolfgang Weisselberg"<ozcvgtt02(a)sneakemail.com> wrote in message >> news:q2lld7-h5u.ln1(a)ID-52418.user.berlin.de... > >>> You need Earth's orbit as a baseline to detect differences >>> for close stars. >> >> But the problem is how to you get two exactly parallel 'rays'. > > There are no such things as light rays they are a useful construction for > computing with geometrical optics. But they are photons too. > The light coming from distant stars arrives as a wavefront and the shape > of the image that is formed is determined by the shape of the aperture > that it goes through. Then that must be for everything we observe. > That is why certain number of leaves of diaphram are preferred. If you > want to see some brutal diffraction effects try putting a small square > aperture mask in front of your longest telephoto lens. But that is a problem with the viewing rather than the 'ray', 'wavelengh' or photon viewed. > > The stars you see at night with the sole exception of the nearby bright > planets are all unresolved and unresolvable with any amateur equipment. So, the planets too were once unresolverable. > They are as good an approximation to a point object at infinity as you are > ever likely to get. True, but that's not the point.
From: Wolfgang Weisselberg on 7 Jun 2010 21:53
DanP <dan.petre(a)hotmail.com> wrote: >> I guess you could do a thought experiment. >> If 2 lenses gather the same amount of parallel rays along >> their lens axis, they must have the same diameter. Go from >> there. > Right, at maximum lens aperture bigger lenses gather more light. > Close the bigger lenses aperture to match the small ones and you get > the same amount of light. Please clarify, what exactly do you mean "to match the small ones"? f/stop? Diameter? Area? What exactly? -Wolfgang |