Sunday, February 17, 2008

Creating cool light trails

Canon 5D, 50mm f1.4 lens, manual exposure of 2.5 second @ f1.6, ISO 400, external flash

Here is another one of my favorite shots of Sawyer. We were sitting on the beach with a great bonfire going and the kids were putting sticks into the fire and then swinging them through the air. I had my camera handy so I figured I'd see if I could make a neat photo out of the action (bearing in mind, it was pitch black out.)

So, I mounted my 50mm f1.4 lens (the lens in my bag the best light gathering capability -- because of it's wide f1.4 aperture). I set the aperture to F1.6 (this lens is 'soft' @ 1.4 - it isn't even very sharp at f1.6, but I was choosing 'gather more light' over 'be razor sharp.) I set the ISO to 400. I used the focus assist feature of my external flash so the camera could focus in the darkness (I originally had the flash set to 'not fire', as the picture I was trying to capture was just the light trail.) I played around with the shutter-speed, eventually deciding that I liked 2.5 seconds (using manual exposure [f1.6, 2.5 seconds.]) This was very much a 'trial and error' process. This combination gave me a great light trail, but I couldn't see Sawyer in the picture at all - just the light trail. So, I thought "I'll use the flash to light Sawyer". I left the manual exposure settings @ f1.6, 2.5 second but turned on the flash and this gave me the exact same 'light trail', but Sawyer was now lit - this made me feel like a photography genius. The default flash settings over-exposed Sawyer, so I tweaked the flash exposure compensation, ending-up with a -1/3 flash exposure compensation. I did also tilt the external flash up about 30 degrees, so the flash didn't 'light-up' so much of the beach. The shot was done hand-held (the flash is what 'freezes' the Sawyer in the photo.) It took about 30 frames before I found the combination of settings that produced this type of photo. I then had to take about 30 more frames to get some 'good' light trails. So it's very much a trail and error process, looking at each image you capture and adjusting 1 setting at a time until you get the image you want. Knowing what to tweak to change the aimge you capture does require an understanding of shutter-speed, aperture, ISO and basic lighting.

Technical details:
  • Lens: Canon 50mm f1.4. I needed a lens that could gather as much light as possible, given it was pitch dark out.
  • Manual Exposure: I used manual exposure for this photo because I wanted 100% control over both the aperture and the shutter-speed.
  • Aperture: f1.6. Given it was pitch-dark out, I wanted an aperture that let in lots of light. The 50 f1.4 produces soft images from f1.4 to f2.0 - I choose f1.6 becuase 'light gathering' was more important that absolute image sharpness.
  • Shutter-speed: 2.5 seconds. Leaving the shutter open for this long is what creates the long light trail.
  • ISO: 400. Higher ISO speed increases the sensitivity of the sensor to light - in essense allowing the sensor to gather more light. But, higher ISO's also have more noise. ISO 400 gave me the balance of gather lots of light - without introducing any noise. In addition, I didn't want to gather 'too much light' as I wanted to keep a black background (at ISO 1600 I saw too much background which cluttered the image.)
  • Flash: I did use my external EX-420 flash for both 'flash assist' (this throws a pattern of red grid-lines on the subject to assist the camera's auto-focus system) and to light the subject. The flash is what illuminates Sawyer in the picture - without the flash all you would see is the light trail. I tilted the flash 'up' 30 degrees, which caused the flash to light the subject, but not the ground.
  • Flash Expsoure Compensation: -1/3. Without any flash compensation, the flash power was too high and Sawyer was over-exposed.

Here are a couple other photos from the evening:

Canon 5D, 50mm f1.4 lens, manual exposure of 2.5 second @ f1.8, ISO 400, external flash


Canon 5D, 50mm f1.4 lens, manual exposure of 2.5 second @ f1.8, ISO 400, external flash

3 comments:

k8et said...

you have some future poi (fire) spinners right there ;o)

http://www.flickr.com/search/?q=poi&w=33437158%40N00

it's a constant game of trial and error, but so much fun (from both the camera side and the spinners side, i do both)

brand new DSLR arrived today, I plan on watching this blog! thanks!

Clint Bogard said...

K8et: Congratulations on the new camera! I like your shots. Come back and share some of your 'winners' with the new camera.

The Rileys said...

I tried this out using my 400d and the 430EX flash. Very nice and even easier than I though it would be. YOu inspired me to give it a try Clint. See for yourself (scroll down to bottom): http://picasaweb.google.com/Photo.Memory.Studios/5208FtBragg

Thanks,

Slade Riley