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Photographer's Note

(Please forgive the mistakes I should have made because of my poor English. Please correct me if you have the time)

Here is a little tutorial. In following it, you would be able to make that kind of picture with all type of numeric camera.

The first step is to take photos of the stars with a long opening time: between 15 and 30 seconds (more would result in having the earth rotation visible). These pictures must be taken with the biggest sensibility of your devise: 400 ISO for my example.
You must take several photos of the same sky or object. There is no limit but be sure to take at least 10 of the best quality.

Between the first and last photos, the earth would have rotated. So, the second step is to superpose the photo with software like Photoshop.
You have to superpose the photos two by two (the other layer must be invisible). You must align them horizontally, vertically and in rotation. In order to do this, put your layer in a subtraction mode. When the result is nearly black you are aligned.

When you have finished, make all the layers visible. Put an opacity coefficient of 100% for the first layer, 50% for the second, 33% for the third and so on. The algorithm is 100/n% of opacity for the nth photo. The aim is to minimize the noise of your devise.

At last but not least, admired the universe!

(bibliography : http://www.astrosurf.com)

sohrab, digi-mom, Emiel_Skyfreak has marked this note useful

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