Night Sky Photography

Canon 5D, EF35mm f1.4 L lens; Sky exposure: 29 sec, f1.4, ISO 1600 Foreground exposure: 481 sec, f8, ISO 1600

Over the past year I have been experimenting with night sky photography. It has been a challenging but rewarding venture.

Along the way I have purchased a wide aperture 35 mm lens (Canon EF35mm f1.4 L). The bright lens helps freeze the motion of the stars by keeping the exposure to around 30 seconds. Even at 30 seconds, if you look closely you can still see motion blur, but at normal viewing distance the stars look sharp.

From the beginning my goal has always been to include the landscape as part of the image. This presents a problem – how to keep both the foreground and the stars in focus, given the extremely shallow depth of field due to the wide aperture of f1.4?

My solution has been to take two exposures, one with the stars in focus and one with the foreground in focus.  These separate exposures are combined in Photoshop. Below are the two separate exposures for the image above. You may notice I have been able to use a much longer shutter speed for the foreground exposure. This is because I am not worried about the tracking of the stars in this exposure and the smaller aperture (F8) allows me to have more of the foreground in focus. In practice it has proved hard to get all of the steps right every time and I have quite a number of duds!

481 seconds, F8, ISO 1600

29 seconds, F1.4, ISO 1600

Here’s a few things I have picked up along the way:

• Try and keep the ISO as low as possible, 1600 works well on the Canon 5D. High ISO noise can degrade the final image quality and cameras vary in their high ISO quality .  There is a trade off here though – you do need to keep the shutter speed down and this requires increasing the ISO. Do your own tests.
• Use the ‘infinity’ setting on your lens focus scale to focus on the stars. Just screwing the focusing ring around as far as it can go will cause the stars to be out of focus, and focusing by eye is not precise enough at F1.4
• Watch for condensation on the lens! This can happen because of dew or cooling air temperatures. I have seen custom made warming pads for lenses but I haven’t had to go that far yet.
• You will need a torch! To aid focusing on foreground objects and to help manually focus the lens.

Here’s some other night sky pictures.

Canon 1Ds mk3, EF24-105 F4L IS USM lens, 297 sec, F8, ISO 400

This entry was posted on Friday, September 2nd, 2011 at 12:49 pm. It is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed.