Archived posting to the Leica Users Group, 2015/03/17

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Subject: [Leica] I got published in Sky & Telescope magazine, but...
From: hlritter at bex.net (Howard Ritter)
Date: Tue, 17 Mar 2015 20:09:17 -0400
References: <D12E30E8.353B0%mark@rabinergroup.com>

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



In reply to: Message from mark at rabinergroup.com (Mark Rabiner) ([Leica] I got published in Sky & Telescope magazine, but...)