Earth Hour

CN Tower during Earth Hour

How I took this shot:
There are tons of excellent tutorials on the web explaining how to capture star trails. But I wanted to capture something a bit different. And here is my experience to share with you. 

Location Toronto is located at the latitude of 43.6 degree North, and the height of CN Tower is about 553m from the base. These mean if I stand at the south of CN Tower looking towards North at the distance of around 580m (553/tan43.6) from the Tower, then I can see the North Star (Polaris) right at the tip of the Tower. As you know, Polaris is the star that is aligned with Earth's axis of rotation. So when Earth rotates, it looks stars are rotating around Polaris. My intention was to find a location that matches the position of the tip of the Tower at Polaris. In this picture you can see the Polaris right at the top of the Tower but slightly off towards left. Initially I found the location on Google Map, but on the spot I figured out it's a bit off and unfortunately the right position was falling in the lake! But I'm still happy with this one.

Timing I was checking out the weather condition regularly for that day. Even though the internet was saying the sky is almost clear for afternoon, but clouds were everywhere up to 6:00pm. I was almost thinking that's not going to happen. But hopefully after 6:00pm the sky started to open up. The Earth Hour started from 8:30pm but I was able to start to capture from 8:45pm since there were some clouds by then.

Camera Settings Using a wide or ultra wide angle is preferred in these shots. First focused on infinity and then set the AF to off. For capturing star trails typically there are two techniques. One is keeping the shutter open for your desired duration (such as 1 hour). This works well where there is no ambient light or "light pollution" such as rural area or out of town places. In urban areas, due to light pollution, this method does not work since the picture will be washed off after few minutes of exposure. Also more ambient light means less stars can be visible in the sky. I intentionally wanted to capture this shot during Earth Hour since I was hoping the buildings around have less lights. But it turned out the only building turned off the lights was CN Tower, which is quite disappointing! So in these situations there is another technique in which continuous long-exposured shots are taken for the similar duration of interest. Then the pictures are blended in post-processing. Due to high level of ambient light, the settings I used were f/4, ISO 100, shutter speed of 5 seconds, and white balance was set to fluorescent. Obviously these are the settings that worked fine for me in this particular situation. Depending on different condition and your subject, you might end up with various settings. But f-number preferably should be kept low (like 2.8, 3.5, 4) since as stars are moving, higher f-stop (which translates to smaller aperture) won't be able to register the light coming out of star on camera sensor. Between 8:45pm to 9:30pm I took 363 shots, each with 5 seconds of exposure, with roughly 2-second interval between two consecutive shots. Needless to say that having a programmable remote shutter release will help you a lot on this. I could not increase the exposure time beyond 5 second because otherwise it would brighten up the image unrealistically. Adding to that, the ISO was already at its lowest, and the f-number could not be increased for the sake of star lights.

Post Processing A freeware (by donation) called Startrails was used to stack up all these 363 pictures. Cool thing with this software is you can see the result on the go, while the program combines each shot to the previous ones. It also enables the user to provide a time-lapse video out of all shots. You also need to have a look at the instruction written by the provider. A final touch-up in Photoshop was included slightly cropping, using curve to adjust the contrast (globally and locally), small increase in color vibrant and slight reduction in saturation, sharpening, and finally adding the copyright text.

Few Notes A portion of Rogers Centre is also visible in the picture at the bottom. Few dotted lines on the bottom-left corner are commercial airplanes which is annoying to have them in the shot. Apparently the best time, for this matter, is after 1:00am when most planes have already landed. Another thing you notice is the the shape of clouds! When I was capturing the images, I saw few clouds are coming and I thought that's gonna ruin my shot. But now I see it actually looks pretty cool! The way that Startrails combines the pictures is that it picks the brightest point at each pixel among all captures during blending. That's how clouds look like this when moving. Next time I may try a longer exposure time (2 hours probably!).

UPDATE: This is the time-lapse video of 363 frames.