|Posted by Joel on September 25, 2012 at 8:10 PM|
This is a tutorial which is near and dear to my heart. Whenever I do a shoot at night I will shoot a star trail shot. There are a few different strategies which I will discuss, and I will detail the method which I use. Also, I will discuss basic knowledge of astrology, and how this can add an extra element to a star trail shoot. This tutorial is in no way a full explination of how star trail shots can be done, it is merely a quick look into the concepts I use. If you would like to know more please email me and I will be glad to explain further. To start this tutorial off I will answer some frequently asked questions about the stars, and shooting star trails.
Why do star trails show up?
The first answer most people have for the existence of star trails is that the stars are moving throughout the night. Although it is true that the stars are moving, they do not move at a fast enough rate to capture with a camera. It is the earth that is in motion, and this is what causes the star trails. Imagine throwing a camera while taking a picture. You wouldn’t say the shot blurred because the subject was moving, it is the motion of the camera that creates the blur. The same is true with star trails, the motion you catch is not created by the stars, it is created by the earth moving.
So we are moving, why does this matter?
If we were documenting the stars moving they would all be in motion, and they would all move at the same speed. However, because the earth is moving there is a point which is always stationary; and this point is the north star. The stars seem to circle around this point, and the further away from this point you get the more the stars move in a given timeframe. Also, when you look to the south you will notice the stars seem to come away from each other. This is because once you pass the 180 degree point you begin to see the stars curve the opposite way. I have set an example of a North Star shot and a southward looking shot to show the differences below.
How can I use this in a photo shoot?
There are many ways to use this to your benefit. If you don’t have much time you can aim south and capture longer star trails in less time. You can also set the north star in a designated spot in a photo, and cause the stars to spin around that spot. I have included an example below.
How do I find the North Star?
As the old spiritual says, follow the drinking gourd; the big dipper points toward the north star. If you imagine the big dipper as a cooking pot imagine pouring water out of the pot. The water would fall on top of the North Star. Here is an image of the big dipper and the north star. I have highlighted the stars in red to make identifying them easier.
Where did it go? Why isn’t the north star in the same spot all year?
Again, back to an old spiritual; the reason that sweet chariot isn’t visible in the winter is because it has swung low. Swing low sweet chariot was sung to tell slaves looking to run north to wait until winter. They did this for a few reasons; water levels along rivers were lower, and night lasted longer, and as they got north they were able to walk along the ice on the river. Be sure to take the season into consideration when trying to find the North Star.
Any other questions?
If you have any other questions please let me know, I am glad to answer anything for you!
For this tutorial I will be expecting that all readers have read my Milky Way tutorial. Some information is the same, and because of this I have shortened a few steps significantly. Plus the other tutorial is just as good as this one, so If you haven't read it yet go do that now and come back to this one!
Step 1: Know the weather
NEVER try a star trail shot without looking the weather up. If there is going to be fog wrap your camera, and if there will be clouds stay in. If you don’t have an hour of clear sky it isn’t worth it.
Step 2: Scouting a location
This is the same as my Milky Way tutorial with a few twists. Always note the direction you are looking. North will capture the spinning of the stars, and south will show the lines moving horizontally. Always note where the North Star is, and set the frame accordingly. If the spin is set in an awkward spot the whole shot can be ruined.
Step 3: Shot settings
There are two ways you can go about star trail shots. You can set the camera on the bulb setting, trigger the shutter with a remote, and leave the filter exposed for the whole shot. The second option is the one I will detail. You can take bracketed exposures and blend them into a single shot in post-production.
How it works:
Set the camera to shoot multiple shots and attach a shutter remote. Set the camera to manual and put the shutter on 30 seconds. Set the ISO high, I would suggest a minimum of ISO 1600. The cool thing about bracketing exposures is the fact that the grain in the shots will be removed by stacking the images. Every time you stack an image you remove some grain from the original image. This means that the more images you stack the clearer the output image will be. I use a floating aperture, which means I change the aperture to wherever I need in order to get a properly exposed shot. Now you just need to point the camera and trigger the remote. When I do these shots I just let the camera keep on shooting until the memory card is full. The longer you leave the camera shooting the better the trails will look. Also, there will be less grain in the final shot because more images will be stacked together.
Step 4: Post production
In Photoshop select:
File: Scripts: Load Files into Stack
From here open all images from your photo shoot, you will have to wait a while for all the images to load in the stack. You will see the images load under the “layers” tab on the right hand side of the screen. Next you will click on the top image in the layer stack. You will see a drop box which says “normal” next to the word layers. Click it and scroll down to the word “lighten.” It will be subtle, but if you look closely you will see the stars start to trail. Continue this last step with all the images in the stack. You will most likely have airplanes in the shot. There is a fun trick to removing these, but if you want to know it you will have to wait for my next tutorial. Until then have fun shooting, and enjoy these sample shots!