Archived posting to the Leica Users Group, 2015/03/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hard on me? Not what I thought at all! I was just letting the inner professor out, not going all defensive on you. Astronomy is one of the few things I feel qualified to expound on to intelligent lay people. ?howard > On Mar 17, 2015, at 7:28 PM, Mark Rabiner <mark at rabinergroup.com> wrote: > > Thanks for the info Howard sorry if I was hard on you. > I shot it too that night and a few years later and it was not f16 rule for > sure but very dark red. I was at iso 6400 and my shutter speeds less than > recommended. As no film I don't think was iso 6400 I could say I got the > shot but could not have in the days of film. At least that's how I felt at > the time. > > > On 3/17/15 4:39 PM, "Howard Ritter" <hlritter at bex.net> wrote: > >> Mark? >> >> Actually, blur due to the Earth?s rotation is not really evident in this >> image. In 2 seconds, an object on or near the celestial equator (like the >> Moon) will move through 30 seconds of arc, which is 1/60 of the Moon?s >> angular >> diameter. In the small image, this is a fraction of a millimeter. I >> cannot >> detect this in my image even when viewed large. The image of the Moon is >> rather poor, since it was taken with a relatively short FL (for an >> astronomical object) of 400 mm, and focus was questionable, since modern >> lenses seem not to need infinity stops any longer (except when they do). >> If >> you look at the stars in the field, you?ll see that there is no >> ?trailing? due >> to the Earth?s rotation, which would affect them the same as the Moon. The >> stars do not quite appear as points, probably again due to imperfect >> focus, >> but they are round, indicating that the exposure was short enough that the >> tiny amount of trailing was small compared to image imperfections. And in >> any >> case, I was not going for a high-definition image of the Moon?s face, but >> of >> the eclipsed Moon in a starry sky. You?re certainly correct that a good >> image >> of the Moon itself, filling the frame or even bigger, would have to be >> made >> with a shorter exposure. Such images are usually made with telescopes on >> motor-driven mounts that track celestial objects. But since the Moon is a >> landscape in full sunlight when it?s not eclipsed, the f/16 @ 1/ISO rule >> of >> thumb works. A camera @ ISO 400 on an f/8 telescope would need a shutter >> speed >> of about 1/800 sec for the un-eclipsed Moon, and the blur due to the >> Earth?s >> rotation without the motor mount would be then about 1/50 of a second of >> arc, >> equivalent to about 100 feet of distance on the surface of the Moon and >> therefore totally invisible when viewed at any scale. >> >> I needed 2 sec @ f/8 and ISO 6400 because the darkest part of the fully >> eclipsed Moon is dramatically darker than the un-eclipsed Moon, on the >> order >> of 1/10,000th as bright, a fact that is not obvious to the visual >> observer. >> >> As for the orbital motion of the Moon, it?s in the opposite direction to >> the >> Moon?s apparent motion in the sky due to the Earth?s rotation, but it's >> negligible in any case. >> >> ?howard >> >> >>> On Mar 17, 2015, at 10:36 AM, Mark Rabiner <mark at rabinergroup.com> >>> wrote: >>> >>> 2 seconds an amazingly long exposure for the fast moving moon. >>> The blur is plainly evident in the image even quite small. >>> >>> http://forums.popphoto.com/showthread.php?338537-Moon-minimum-shutter-speed >>> >>> >>> On 3/16/15 5:13 AM, "Peter Dzwig" <pdzwig at summaventures.com> wrote: >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information > > > > > -- > Mark William Rabiner > Photographer > http://gallery.leica-users.org/v/lugalrabs/ > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information