1 ACCEPTED SOLUTION
Ahhh! This is completely different.
I suspect you'll find, as Skirball points out, that your camera likely has "Long Exposure Noise Reduction" enabled. This feature kicks in automatically for "long" exposures. The camera counts the exposure time for long exposures. When the shot is done, it takes a 2nd exposure but this time it does not open the shutter. So basically it is taking a photo with the shutter closed merely so that it can allow the "noise" from long exposures to accumulate. It then uses that to subtract noise from the original image.
This doesn't actually eliminate noise... it merely reduces some of it. This is because some noise is pattern noise can can reappear in the same spots and some noise is random. There are a lot of techniques we use when doing astro-imaging to reduce noise which are even better but that's getting off topic.
Meanwhile back to your star trace...
There's a free application you download called StarStax. It's one of the most popular programs for doing what you want and it's available on Winows, Mac, and Linux.
If you take one really long exposure, you'll find that your background image of the sky turns to mud and you can't actually see anything.
I'll give you an example.
This is a 4 minute exposure using my 60Da. The object you're having a difficult time seeing in this image is the Dumbbell Nebula (a planetary nebula) -- it's also known as Messieer 27.
But the real reason I'm showing you this is because this is what happens when you take a 4 minute exposure in suburban skies... all that brownish muddy backgrond isn't a defect in the camera... this is actually a very good exposure. This is what light pollution does. Had I allowed this exposure to just keep going, the muddy data would just keep building up getting stronger and stronger.
Obviously this is not what you want. Incidentally... if I had traveled far far away from the light pollution of any city or town, I could have captured a much longer exposure without things being so bad.
This next exposure is the same object... but using a lot of imaging processing to clean it up. Also, I took 16 of these 4 minute exposures as well as 8 dark exosures (exposures using the same exposure settings except leaving the camera covered so all it can capture is darkness and "noise" which the computer can use to help clean up noise inside the image.) There are some other techniques we use as well.
This is a processed version of the same object.
To get good star trails, you'll need:
(1) very good dark skies (the darker and farther from urban and suburban light pollution... the better.)
(2) a moonless night (the moon adds an astonishing amount of light pollution and if you take the images with the moon you might as well just be taking them light polluted urban skies)
(3) the remote timer and tripod you already have.
Set the camera to take 30 second exposures.
Turn off "long exposure noise reduction"
Set the camera to take exposures "continuously" (e.g. you'd normally associated this with shooting sports... e.g. capturing action at 5 frames per second, etc.) except you can actually put the camera into "continuous" shooting mode, set the shutter to 30 seconds, and then just press and lock the shutter button on the remote release and go enjoy some coffee for a few hours. The camera will take a new image every 30 seconds.
When you're done, import all the images into StarStax and let it process and merge the images.
The application will end up creating star trails... but since the exposures were shot in dark skies and relatively short (for night photography) exposure times of just 30 seconds, you should not have a muddy sky background.
You can find LOTS of YouTube videos on doing this, btw.
Good luck!
Ahhh! This is completely different.
I suspect you'll find, as Skirball points out, that your camera likely has "Long Exposure Noise Reduction" enabled. This feature kicks in automatically for "long" exposures. The camera counts the exposure time for long exposures. When the shot is done, it takes a 2nd exposure but this time it does not open the shutter. So basically it is taking a photo with the shutter closed merely so that it can allow the "noise" from long exposures to accumulate. It then uses that to subtract noise from the original image.
This doesn't actually eliminate noise... it merely reduces some of it. This is because some noise is pattern noise can can reappear in the same spots and some noise is random. There are a lot of techniques we use when doing astro-imaging to reduce noise which are even better but that's getting off topic.
Meanwhile back to your star trace...
There's a free application you download called StarStax. It's one of the most popular programs for doing what you want and it's available on Winows, Mac, and Linux.
If you take one really long exposure, you'll find that your background image of the sky turns to mud and you can't actually see anything.
I'll give you an example.
This is a 4 minute exposure using my 60Da. The object you're having a difficult time seeing in this image is the Dumbbell Nebula (a planetary nebula) -- it's also known as Messieer 27.
But the real reason I'm showing you this is because this is what happens when you take a 4 minute exposure in suburban skies... all that brownish muddy backgrond isn't a defect in the camera... this is actually a very good exposure. This is what light pollution does. Had I allowed this exposure to just keep going, the muddy data would just keep building up getting stronger and stronger.
Obviously this is not what you want. Incidentally... if I had traveled far far away from the light pollution of any city or town, I could have captured a much longer exposure without things being so bad.
This next exposure is the same object... but using a lot of imaging processing to clean it up. Also, I took 16 of these 4 minute exposures as well as 8 dark exosures (exposures using the same exposure settings except leaving the camera covered so all it can capture is darkness and "noise" which the computer can use to help clean up noise inside the image.) There are some other techniques we use as well.
This is a processed version of the same object.
To get good star trails, you'll need:
(1) very good dark skies (the darker and farther from urban and suburban light pollution... the better.)
(2) a moonless night (the moon adds an astonishing amount of light pollution and if you take the images with the moon you might as well just be taking them light polluted urban skies)
(3) the remote timer and tripod you already have.
Set the camera to take 30 second exposures.
Turn off "long exposure noise reduction"
Set the camera to take exposures "continuously" (e.g. you'd normally associated this with shooting sports... e.g. capturing action at 5 frames per second, etc.) except you can actually put the camera into "continuous" shooting mode, set the shutter to 30 seconds, and then just press and lock the shutter button on the remote release and go enjoy some coffee for a few hours. The camera will take a new image every 30 seconds.
When you're done, import all the images into StarStax and let it process and merge the images.
The application will end up creating star trails... but since the exposures were shot in dark skies and relatively short (for night photography) exposure times of just 30 seconds, you should not have a muddy sky background.
You can find LOTS of YouTube videos on doing this, btw.
Good luck!
