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by garik

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Since I am usually taking pictures under low light ambient conditions I have discovered the nifty 1.4 lenses (such as the Sigma 30mm/1.4 or the Canon 50mm/1.4 or also the Canon 85mm/1.8) for my Canon 550D. My main problem is not that there's not enough light to capture images, but that the autofocus – usually with one fixed AF point – is rather slow under those conditions, if it can focus at all.

My main subjects are dancers, who are quite naturally moving, so speed is an issue, especially with the narrow DOF the 1.4 or 1.8 aperture gives.

What can I do?

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4  
Should you not find an answer (as may be at the limit of what your camera and lens can do), I suggest the if you cannot beat them, join them approach: Manual focus, smallish aperture and slow shutter-speed (but still above 1/focal-length). That way you'll get the blur from the dancer's motion on a sharp background which will emphasize their movements. –  Itai Jun 26 '11 at 14:17
    
I ended up buying better camera bodies, in the end switching to Nikon (D700) because the focus system was way better. –  Sam Jun 28 '11 at 13:41

4 Answers 4

up vote 6 down vote accepted

some ideas, based on the assumption that AF systems have it easier in areas with more light, detail and contrast:

  • If the floor has some detail (e.g. it's made of wooden planks) focus easily on a well lighted area, lock focus and wait for dancers to get there. Then shoot repeatedly.

  • Use a simple focus trap, it's basically like this: focus somewhere, press the shutter release button, keep it down until the camera gets the subject focused in the point you selected and actually shoots. How (and if) it's possible to do this depends on your camera. It's quite easy with Nikon DSLRs, it also should work with Pentax cameras if you know what you're doing (I tried fiddling with a K200D but couldn't get it to work the way I meant). I don't know about Canons.

  • Most DSLRs have different types of AF sensors, often it's cross-type opposed to "just plain", cross-type being more accurate. You could try making sure you use those points (usually, on less-than-top-level cameras it's just one cross-type sensor, the center one) to get better AF, but I'm not sure this will make things faster.

  • Focus on most detailed areas of the dancer's body (face, edge of the dress, lines where clothes of different colors meet).

  • General advice: always look for detail or contrasts to speed up AF operation. Like a crack on a white wall, a bracelet or watch on someone's arm, the line between someone's hair and cheek skin, the lines beetween wooden planks on the floor.

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You can use the ST-E2 which gives you a focus assist beam without the bulk of a flash. http://www.amazon.co.uk/Canon-Speedlite-Wireless-Remote-Transmitter/dp/B0000C4G95/

There is further discussion on the matter here: http://www.jwz.org/blog/2009/11/alternatives-to-canon-speedlite-transmitter-st-e2/

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1  
+1, but wow, that is freakishly expensive for what it is. –  mattdm Jun 26 '11 at 15:30
    
Welcome to the world of Canon accessories, I hope you brought your wallet! –  Matt Grum Jun 26 '11 at 17:35
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Just for the record, my Canon Speedlite 430EX II does this also (costs the same, but works as an actual flash also) –  ChrisFletcher Jun 26 '11 at 17:40
    
@MattGrum - correction: welcome to the world of brand name accessories... –  ysap Jun 27 '11 at 17:16
    
The Metz 24 AF-1 is about £60 and not much bulkier. Has a focus assist light and is a compact (bounce) flash, but is not a wireless controller. –  mattdm Jun 27 '11 at 18:49

In addition to focus assist mentioned by Guffa, some more ideas to try:

  • Assuming lighting is uneven, anticipate when the dancers are in brighter areas - it will be easier to focus when there's more contrast. It will also work favorably for composition - brighter areas call for attention, so you want your subject there anyway.

  • Compose with more room around dancers. It requires you to either shoot from further away or use a wider lens - both way you will be shooting closer to hyperfocal distance so focusing takes less adjusting and missed focus is not as noticeable.

  • Use AI Servo focusing so the camera would try to keep focusing and be ready to shoot when you fully press shutter.

  • When you get a well-focused photo, switch to manual focus and wait until the dancers return to same spot.

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What I also learned about autofocus: more contrast = better –  danieldekay Aug 15 '13 at 9:44

You can put a flash on the camera that has a focus assistance beam. You can set the camera to not use the flash, but still use the focus assistance beam.

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Good idea – have to try that. But I would like to have as little disturbance to the dancers as possible… –  danieldekay Jun 26 '11 at 13:49
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@d'ombre: The focus assistance beam is usually a single color, red or green, so it's not as disturbing as a white light. Eventhough, maybe you should inform the dancers how and why you are using the flash, so that they know that there won't be flash photography. –  Guffa Jun 26 '11 at 13:53
    
Well, actually even the AF beam is disturbing. Not as much as a flash, but enough :( –  danieldekay Aug 15 '13 at 9:43

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