Share your Astrophotography Photos

[lindam]

Are you a fan of astrophotography? Post your favorite photo you've taken and share the story behind it. Be sure to include the Canon gear you used.

[kvbarkley]

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@RobertTheFat wrote:

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@kvbarkley wrote:

Probably my third, but thanks.

I feel guilty because here in NM there is no shortage of dark and clear skies.

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You feel guilty because your state hasn't indulged itself in universal light pollution? Somehow that sounds backwards.

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No, I feel guilty because I have not taken advantage of it. I do have lots of pictures of balloons during golden hour. The Albuquerque Balloon Fiesta is one of the few events that takes place at sunrise. 8^)

[ebiggs1]

I am pretty clear to the South but not good towards the North.  Kansas City is 40 miles to the North.  Almost nothing to the South.

[ebiggs1]

Oh. BTW, that was the ef 70-200mm f2.8L II at 105mm @ f4 on a 1Ds Mk III.  ISO was1600.

[TheCanon]

How long of an exposure would this type of shot be?

[RobertTheFat]

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@TheCanon wrote:

How long of an exposure would this type of shot be?

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You can see where the center of rotation is, and you know that a full rotation takes 24 hours. So measure the radius of any of the circles being described; then use your high school geometry to compute the arc length from the chord lengh of the corresponding trail, and determine what percentage of a full circle the arc length is.

[ebiggs1]

You can see the brighter streaks of the stars is not too long. Could be an hour. The camera is pointed towards Polaris.

A good starting setting of ISO 400 at f/2.8 or f/4 might work.  Depending on how much light pollution, or dark skies, you have at your place, an exposure as short as 30 seconds might work. At darker sites, you might be able to expose much longer.  Exposures that are too long will deteriorate quickly because of noise and heat. Plus some other factors like atmosphere distortion.

Might be two shots, too!  

[ebiggs1]

Bob from Boston,

"You can see where the center of rotation is, and you know that a full rotation takes 24 hours."

Not really.  Several short exposures of, say 6 or 8, of approx. 5 to 10 minutes can do that.  It also eliminates a lot of error factors from long exposures. Another trick astro-photographers use is a 'fill flash' at the end to make foreground subjects show up more.  But in that shot I suspect the foreground trees would be washed out unless they were shot separately. Possibly in just one shot.  Don't you think?

[RobertTheFat]

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@ebiggs1 wrote:

Bob from Boston,

"You can see where the center of rotation is, and you know that a full rotation takes 24 hours."

Not really.  Several short exposures of, say 6 or 8, of approx. 5 to 10 minutes can do that.  It also eliminates a lot of error factors from long exposures. Another trick astro-photographers use is a 'fill flash' at the end to make foreground subjects show up more.  But in that shot I suspect the foreground trees would be washed out unless they were shot separately. Possibly in just one shot.  Don't you think?

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Yes, really. The Earth does a full rotation in 24 hours, regardless of how many exposures one takes to document the process. The answer to the question is the total exposure time; whether and how that time was broken into individual exposures is an implementation detail.

If the fill-flash method were what was used to illuminate the trees I'd expect them to show some color. As it is, they appear backlit (presumably by light from a city, given the pinkish color). I don't think it's necessary to posit a separate exposure for the trees, but it's certainly a possibility.

[Waddizzle]

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@TheCanon wrote:

How long of an exposure would this type of shot be?

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Comparing the length of outer arcs to how much time an hour hand on an analog clock would take to travel that far, I would say it looks to be roughly about an hour.  However, most clocks are 12 hour displays and the Earth takes a full 24 hours to do a full rotation. 

In other words, what ever your estimate is for how much travel by an hour hand is....double it.  I'd venture that the shot is somewhere around a 2-3 hour sequence of stacked exposures.  How many is anyone's guess.  I would not be surprised if the total was closer to 100 shots than 10 shots.

Others things to note are the angle of view and the angle to the apparent horizon of the center of axis of rotation, either the North Star or the South Star.  The angle of view isn't very wide, but it isn't very narrow either.  I'd venture to guess that a focal length between 50mm and 200mm was used. 

Furthermore, the polar stars are not as close to the horizon as the shot might seem to suggest.  I'd venture that it was taken at the bottom of a hill, looking up towards a ridgeline of trees at the top of the hill.  There are numerous free applications to help you find the North and South stars once you know your current GPS position, date, and time of day.

[RobertTheFat]

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@Waddizzle wrote:

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@TheCanon wrote:

How long of an exposure would this type of shot be?  

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Others things to note are the angle of view and the angle to the apparent horizon of the center of axis of rotation, either the North Star or the South Star.  The angle of view isn't very wide, but it isn't very narrow either.  I'd venture to guess that a focal length between 50mm and 200mm was used. 

Furthermore, the polar stars are not as close to the horizon as the shot might seem to suggest.  I'd venture that it was taken at the bottom of a hill, looking up towards a ridgeline of trees at the top of the hill.  There are numerous free applications to help you find the North and South stars once you know your current GPS position, date, and time of day.

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The last I knew, there was no South Star. Has one been discovered while I wasn't paying attention?