[Leica] I got published in Sky & Telescope magazine, but...

[Howard Ritter]

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 Earthąs 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 Moonąs 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, youąll see that there is no łtrailing˛ due
>> to the Earthąs 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 Moonąs face, but of
>> the eclipsed Moon in a starry sky. Youąre 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 itąs 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 Earthąs
>> 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, itąs in the opposite direction to the
>> Moonąs apparent motion in the sky due to the Earthąs 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:
>> 
>> _______________________________________________
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> 
> 
> 
> 
> -- 
> Mark William Rabiner
> Photographer
> http://gallery.leica-users.org/v/lugalrabs/
> 
> 
> 
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