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Best Seat in the House

Photography, sports and life as seen through the lens of Seattle Times photographer Rod Mar.

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September 29, 2007 11:17 PM

A Flicker of Light

Posted by Rod Mar

(Warning: this post gets fairly geeky and technical and I have really no idea what I'm writing about, so I hope some of you will write me and explain the phenomena. So if you're waiting for more blondes doing beer-bongs , you'll have to wait some more).

I've written a lot about lighting challenges in the past year, including lights that change color from frame to frame . Sometimes in arenas with sodium vapor and mercury vapor lights, the color temperature changes from millisecond to millisecond, changes that are invisible to the naked eye but make balancing color difficult.

Friday night I encountered a new challenge — lights that flicker in output from frame to frame.

While shooting O'Dea's total domination of Bainbridge at West Seattle Stadium, I decided to shoot ambient light and to not use on-camera flash. On-camera flash is often a necessity , but if the ambient light is even close to providing enough light, I'll shoot available.

The light was dark, but not too dark. ISO 1600, with a shutter speed of 1/320th of a second. 1/320th is not quite fast enough to freeze player motion, but I figured that I could get enough close ones to have three or four publishable frames.

As I was reviewing frames to check the exposure in the first quarter, I noticed something odd about the images:


Notice how the exposure changes and is brighter in the middle frame? Weird. I was shooting with the motordrive on a Canon EOS 1D Mark IIN at 8 frames per second. Apparently the lights flicker fast enough not to be noticeable to the naked eye, but slow enough to be caught by the camera shutter.

Then I had a decision to make. Add the flash and eliminate the flicker? If I did that, I would have the possibility of horrible shadows and red-eye, but I wouldn't have the flicker. But heck, I wanted the challenge, so I decided to shoot available light and hammer on the shutter in hopes of shooting "through" the dark frames.

I'd been trying hard to get some nice frames of O'Dea's Jorhi Fogerson, and he finally came my way on a sweep to the right side. I've also decided to bump the shutter speed to 1/400th of a second, figuring the "bright" frame in each burst would be close to properly exposed at that speed:


This screen grab from Photo Mechanic (the photo editing program we use) shows all the pertinent technical information, as well as an informative histogram at lower right. The histrogram shows where the light is falling on a scale from shadow (left side) to highlight (right side):


Just so I can claim to be all techy and geeky about my work, here's the histograms for frame #4000 (the center frame of the second burst shown above:

Notice how much more light is in frame #4000 than in the histogram from the frame after it (frame #4001). You can see how much more light is falling towards the middle of the graph. Remember that the left side refers to the shadow/dark area, and the right side is the highlight area. The more light to the left, the lower the exposure, the more light to the right, the higher exposure:


I told you. Geeky.

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Posted by SeaHokie

2:54 PM, Oct 01, 2007

And to think Polaroid's "60-second excitement" once seemed the pinnacle of space-age photo technology!

Posted by Jeffrey Friedl

5:47 PM, Oct 01, 2007

What kind of lights do they have at the stadium? A lot of light sources flicker on and off faster than human perception. (Because they spend more time off than on, such lights tend to be energy efficient.)

If the light flickered off half way though your 1/400th of a second shot, it turns it into a 1/800th of a second shot, and hence the darker result.

Posted by Mr Michael

8:19 PM, Oct 01, 2007

Wow, look at the shift in the Blue/green side... yikes! Hard to tell from these histograms, but it looks like red is constant... which makes a kind of sense. It wouldn't be so bad if the lights' flickering was unsynchronized, that way everytime one of the lights is 'dim' the rest would still be bright... but I'll bet the flickering is synchronized to the common power source. If you want to go full geek, ask the guys at the "Pro" stadiums if they make sure to keep the flickering of their lights staggered... it wouldn't surprise me if they did that for the TV cameras' sake.

It's actually interesting, in a technical kinda way. I can't think of anything YOU can do to avoid it, and it's probably too much to ask the Stadium Maintenance crew to look into the problem. ;) However, whenever the parents ask why you couldn't publish a photo of THEIR kid making the touchdown, you can always blame the flickering lights.

I'll bet if you take a spinning top or something to the stadium you could get it to 'strobe' to a stop when it syncs up to the lighting... useless but fun trick... unless you could use that to tell ahead of time if there will be a flickering problem at other venues?

Also, why not set the camera's exposures to the dark frames? There seems to be more of the dim than the bright ones. Of course, you only showed us a few.

Posted by Hank Ebert

7:14 AM, Oct 02, 2007

Thank you, thank you, thank you!!! I thought I was going to have to send my camera back to the factory. I was shooting high school football and getting different exposures and color balances of the same scene. Someone posted this URL from the Fred Miranda photography forum. What perfect timing!

Great column on photography, by the way!

Posted by Rod Mar

12:01 AM, Oct 03, 2007

guys,

thanks for your comments. mr. michael, that's a great point about the staggering of lights at the pro stadium. i'm gonna ask.

as for setting the exposures for the dark frames, i was already at ISO 1600, 1/320-400 f2.8 for the underexposed BRIGHT ones, so the dark ones are probably ISO 1600, 1/200 f2.8 at best.

the mark II's are okay up to 1600, garbage after that.

i'm playing with some new mark III's, so i'll let you know how it goes. they're supposed to be good up to ISO 3200.

hank -- thanks for reading, and i'm glad i could help!

thanks again, everyone.

rod

Posted by Pete from Dayton

12:31 PM, Oct 03, 2007

Another option is to use the flash on, say 1/2 or 1/4 power (maybe even 1/8) to help out.

Take the flash and mount it below the camera (on the monopod) and it helps with the red-eye problem. (Not perfect, but then, what is?)

Since the first frame appears darker (if we are seeing the first frame of a play on the left,) then you'd have a balance and the flash wouldn't be overpowering.

I know, I wish they'd start high school games an hour (at least) earlier to help with lighting, too, but they haven't shown any interest in that idea so far.

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