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(The New York Times)   Gallery of what a clear night sky over major cities would look like without light pollution   (nytimes.com) divider line 62
    More: Interesting, light pollution, night sky  
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5838 clicks; posted to Geek » on 12 Feb 2013 at 6:02 AM (2 years ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



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2013-02-12 09:08:01 PM  

0Icky0: gaspode: Well there you go. maybe, given I have the most glorious view of Eta imaginable from here, I need to spend some time just laying on the ground looking at it to see if I can detect that hint!

Remember, you can't look directly at it.
I first noticed it off to the right when looking at the Southern Cross.
If I remember correctly, it disappeared when I looked directly at the nebula.


Yeah I know that trick, been watching Comet Lemmon the last days through binoculars in the same way, centre of the view offset makes it much brighter, fascinating to watch its progress past the pole..
 
2013-02-12 09:17:05 PM  

gaspode: Yeah I know that trick, been watching Comet Lemmon the last days through binoculars in the same way, centre of the view offset makes it much brighter, fascinating to watch its progress past the pole..


Man, I have to get out of Hong Kong if I want to see any of the upcoming comets.
 
2013-02-12 09:19:23 PM  
This is pretty much what any moonless clear night looks like above my house. Then again, I'm 4 hours from the nearest major city.
 
2013-02-12 11:37:59 PM  
Yeah, I'm sorry... I've seen the sky from above the upper Merced in Yosemite -- so dark zero ground visibility -- zero humidity at high altitude -- nothing near this spectacular -- these are long exposures
 
2013-02-13 09:25:46 AM  
Two points:

1: If you use a long exposure on night sky, the stars will show up as curved lines.

2: A camera can pick up hues that the human eye cannot. So, the "hues" you may see in photos of stars may appear vivid, but that does not mean it's been artificially altered.
 
2013-02-13 09:31:35 AM  

Rufus_T_Firefly: If you use a long exposure on night sky, the stars will show up as curved lines.


Unless you use a tracking mount. Of course, that makes the ground blur -- but if you're using Photoshop to strip two images together, you just make sure that the blurred ground is below the mask for the sharp foreground in the final image.
 
2013-02-13 09:51:07 AM  

jfarkinB: Unless you use a tracking mount...


Thanks, I forgot to add that method.
 
2013-02-13 11:15:14 AM  

Rufus_T_Firefly: 1: If you use a long exposure on night sky, the stars will show up as curved lines.


I would think that your average long exposure on your typical DSLR, about 32 seconds at maximum, wouldn't really curve/blur that much.  I could be wrong, and will see when I try it.
 
2013-02-13 11:39:19 AM  

Shadowknight: I would think that your average long exposure on your typical DSLR, about 32 seconds at maximum, wouldn't really curve/blur that much.  I could be wrong, and will see when I try it.


Depends on the focal length. If you're taking a really wide-angle shot like this, you might get away with it. Let's see...

The stars describe a 360-degree arc in 24 hours, more or less. That's 15 degrees per hour, 4 minutes per degree. In half a minute, 1/8 of a degree.

If the star's at the pole, this means no trail at all. Stars at the celestial equator will leave the longest trails.

Assume you're using a really wide lens, giving a 90-degree field of view across the long axis of the image. On a 16MP camera, that's around 4500 pixels, 50 pixels per degree. In 30 seconds, a star would trail across 50/8 = 6.25 pixels.

A 90-degree horizonal FOV represents a really wide lens -- something like 17mm on a 35mm sensor, or 11mm on an APS-C sensor. A more typical lens will have a narrower FOV, which means the trails will be longer (cover more pixels).

In my experience, even with a really wide lens (10mm on a Canon 20D), stars trail enough to "look funny" on a half-minute exposure. You can stack multiple shorter exposures, but it's not as good as a single long tracked exposure.
 
2013-02-13 11:50:04 AM  
jfarkinB: Lots of calculations...

Damn, man, and I thought I was into photography.  I would have never done all this smarts stuff, just tried it and saw what happened.  I bow to your superior shutterbuggery.
 
2013-02-13 12:07:02 PM  

Shadowknight: I would think that your average long exposure on your typical DSLR, about 32 seconds at maximum, wouldn't really curve/blur that much.


According to the photographer in the link I provided, you will see effects on stars (depending on the lens) after 15 seconds.
 
2013-02-14 01:22:13 AM  
yeah completely lens dependent, but if you arent going very high res then 30 seconds is not a bother. if there is no ground in the shot then there is no need to not track though. For full res use you would pretty much need to track for anything at all over 10 seconds.. you can use the 'long exposure then flash at the end' trick to bring some trees or something in if you are clever.

that said, 30 seconds in a dark place is plenty to get heaps of colour in your images, especially with a wide aperture, and if you are websizing it then you will get amazing results from almost no work.
 
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