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Thread: What length lens for ...

  1. #1
    PopsPhotos's Avatar
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    What length lens for ...

    http://www.space.com/11310-huge-aste...-november.html

    Mark your calendars for an impressive and upcoming flyby of an asteroid thatís one of the larger potentially perilous space rocks in the heavens Ė in terms of smacking the Earth in the future.

    Itís the case of asteroid 2005 YU55, a round mini-world that is about 1,300 feet (400 meters) in diameter. In early November, this asteroid will approach Earth within a scant 0.85 lunar distances. [Photo of Asteroid 2005 YU55]
    Initially, the object will be too close to the sun and too faint for optical observers. But late in the day (Universal Time) on Nov. 8, the solar elongation will grow sufficiently to see it. Early on Nov. 9, the asteroid could reach about 11th magnitude for several hours before it fades as its distance rapidly increases, Benner explained.
    One of my students has the 500-1000 mirror for her Canon. Maybe ...

    Pops

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    Steaphany's Avatar
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    Re: What length lens for ...

    Remember that the moon has a diameter of 3,476 km and at a mean distance of 384,400 km from Earth only leaves an object that is roughly 0.5ļ. A minor planet or asteroid that is only 400 meters across, even as close as 0.85 lunar distances, 326,740 km, will still look like a point.

    Think about the origin of the word "Asteroid", it means Star-Like since the early discoveries of asteroids were seen as star like points in the telescopes of the day.

    The key difference is that 2005 YU55 will be moving very fast compared to the background field of stars, and the closer it gets, the greater it's motion will be.

    Instead of going for a 1,000 mm or longer lens, go for a shorter focal length with a large aperture, to collect lots of light. Remember, the only way 2005 YU55 will stand out is if you can capture the back ground stars. You may want to calculate the lens field of view and select a lens that will capture enough sky to recognize the constellations. Now, here is a disappointment for many, Looking at the sky, you'll just see points of light. Unless you're well versed with the constellations, you may never recognize 2005 YU55, besides, you'll probably never even be able to see it.

    the asteroid could reach about 11th magnitude
    Even at the best of conditions with your eyes completely dark adapted, you can only see objects brighter than the 6th magnitude.

    Put your camera on an equatorial or alt-azimuth mount and shoot a photograph where the camera is tracking the star motions. Even a 1 minute exposure will leave 2005 YU55 as a streak as the back ground stars remain as points.

    If you only have a static tripod, then hook up your intervalometer and shoot a succession of frames that you assemble into a time lapse video. A time lapse will have the star background moving across the sky while 2005 YU55 will be zipping by in a completely different direction.
    Last edited by Steaphany; 10th April 2011 at 03:48 PM.

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    PopsPhotos's Avatar
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    Re: What length lens for ...

    I posted this partly as a joke, as the lead in when I found it was saying it would be a photo opportunity. Even so, I thought some here might be interested it watching for it. I know I will be out there, dumb as that activity might be.

    Pops

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    Steaphany's Avatar
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    Re: What length lens for ...

    Quote Originally Posted by PopsPhotos View Post
    I posted this partly as a joke
    Pops,

    Joke or not, it is an interesting astronomical event that could yield a challenging effort to capture something that doesn't happen every day. ( Set things up, hope it all works, and only later would you know if you caught this once in a lifetime event. ) Remember, 2005 YU55 will be 100 times fainter than the dimmest stars you could possibly see with unaided vision and the only proof you'll ever have that you actually caught 2005 YU55 with you camera is a streak of a long exposure or by comparing multiple exposures, as in a time lapse, to recognize it's motion.

    For students, it is a wonderful exercise testing many real world photography skills.

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