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Old Mar 27, 2005, 2:53 PM   #1
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I would like to take such photo but my SONY DSC-V3 does not have "B" time....the maximum time is - as I remember - 30 seconds. But the lense should be opened for 30-40 minutes.

How to solve this problem?
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Old Mar 27, 2005, 9:25 PM   #2
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I've seenthis product mentioned for capturing star trails (it allows you to stack multiple images):

http://www.tawbaware.com/imgstack.htm


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Old Mar 28, 2005, 3:21 AM   #3
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Hi!

This software looks a real helper and just invented to solve such problems like mine. :idea:

I gonna buy a tripod (do you have any advice?) and try it as soon the weather will be clear - now it is raining here in Hungary (Europe).

Thank you!
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Old Mar 29, 2005, 4:11 AM   #4
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how do u do that star trails stuff? looks pretty cool. I might want to try it out.
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Old Apr 6, 2005, 10:24 PM   #5
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Folks, it's just a simple long exposure.

I've heard of some strange answers for this one. But here is the way to do it, without any software help

LONG EXPOSURE!

The first thing you have to do, is have a digital camera that can be programmed for ANY shutter time. If you don't own one (and i don't know which dSLR's support this) then yes, you will have to use software compilers.

Standard night sky around midnight, WITHOUT moon.

Shutter Time: 2 hours - 5 hours depending on camera and aperture

Aperture, i would use an aperture of 3.5-5.6

ISO: 100 (50 if you have it)

If you have noise reduction software, USE IT.

And NO, the stars moving in a circle, is NOT a photoshop trick, it actually happens. The earth moves on it's axis, and the stars will move in a circle motion. the ONLY star that will not move (only slightly during certian times of the year) is the North Star, as it is right on the earth's axis.

-Travis-
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Old Apr 7, 2005, 7:20 PM   #6
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Get a camera that will have a long time open, but expect to run down a lot of batteries, or hook up with a A/V adapter.
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Old Apr 8, 2005, 5:32 AM   #7
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what do u use to hold down the button to take pictures?
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Old Apr 8, 2005, 7:16 AM   #8
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Guys, I think you're all missing the point here. The original poster's camera is limited to 30 seconds.

This is one area (longer exposures) that film still has an advantage.

The sensors used in Digital Cameras have a problem with noise and hot pixels (where a pixel turns on to it's maximum brightness) when exposure times get long. As a result, sophisticated "dark frame subtraction" noise reduction systems need to be incorporated. These systems are designed to replace the hot pixels with values from adjacent pixels as they occur (and the longer the exposure, the greater the number of hot pixels).

To accomplish this, a second exposure (dark frame) is taken with the shutter closed to identify pixels that are likely to be hot in the actual exposure. Since the shutter times are the same in both photos, chances are, the hot pixels will occur in the same locations. So, the camera knows where to find them in the actual exposure. But, this is not foolproof.

It's not uncommon for an image from a modern digital camera to have hundreds of hot pixels on a relatively short exposure (15 seconds or so). But, you just don't see them because of the noise reduction system. However, the longer the exposure, the greater the chance of error (hot pixels in the actual exposure that are not in the dark frame exposure -- so they won't get mapped out), and the more of the image that is being lost due to hot pixel replacement (you'relosing real pixels as the noise reduction replaces them).

Pixels that are noisy, but not yet bright enough to trigger the thresholds for what is or is not a hot pixel also become a problem at longer exposures.

Now, a DSLR model is much better in this area. But even these are likely to have problems on very long exposures (you just may not see most of them after noise reduction is applied).They're better suited for this type of photography since their much larger image sensors are less prone to noise and hot pixels, compared to the smaller sensors used in non-DSLR models.

But, they're not as good as film for longer exposures either. Heck, not long ago someone was having problems trying to do this type of thing with a D30 in the forums here (and it has larger photosites for each pixel than mostother cameras).

Some newer models are much better. For example, the newer Canon CMOS sensors in their DSLR models seem to do abetter job onlonger exposures (I've seen some relatively clean 30 minute shots with them).

But, you don't*have* to take star trails with a single long exposure. There are software products designed to let you combine multiple images taken over a longer period of time for this purpose. One of them is Image Stacker:

http://www.tawbaware.com/imgstack.htm

Here are examples of Star Trail images combined using it:

http://www.tawbaware.com/maxlyons/cgi-bin/image.pl?gallery=8

Here is another technique for blending multiple exposures into one.

http://luminous-landscape.com/tutori...blending.shtml

Even film can have problems on very long exposures (reciprocity failure). So, combining more than one exposure can be a useful technique (and can be the only technique if you want to capture star trails with the vast majority of digital cameras, since noise levels and hot pixels would ruin the photos otherwise).


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