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I have seen sports photography where the background is completely wiped out (black) during daylight. I'm trying to achieve a similar (pure black background) effect with no extra gear, just a DSLR camera (Canon 20D).

I think this is doable using sync speed (where the sensor is fully exposed to the flash burst), closer flash burst to the subject, and some suitable shutter setting. How can I minimize light to the sensor before 120th of a second at ISO 100?

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I'd be interested to see an example. Maybe a ND filter was involved, to darken the background. –  sebastien.b Oct 19 '10 at 16:17
    
An example will help us determine how he did it, i.e. multiple flashes, a flash very close to the subject, etc. –  Eruditass Oct 19 '10 at 17:04
    

2 Answers 2

up vote 11 down vote accepted

To overpower the sun during the day you need either very high speed sync (i.e. with a leaf or electronic shutter), or tons of light and an ND filter.

The theory is that the exposure from a flash is practically unaffected by the shutter speed, so by using a high shutter speed you let in the same amount of flash but much less ambient light, allowing your flash to overpower the ambient.

The problem is, with most cameras, including your 20D you can't shoot past 1/250s when using the flash, as beyond that the second curtain starts closing before the first has fully opened and your flash is only visible in part of the image.

Some new flashes offer high speed sync, which pulses the flash to act like a continuous source. The problem with this approach is that when you up the shutter speed you let in less flash as well as less ambient so you don't gain anything. Some people combine several flashes to compensate for the loss of light, but in mist cases there's no difference between multiple flash HSS, and using tons of flashes with normal sync plus an ND filter. Here's a good post about using HSS to get the effect you want with multiple flash units: http://strobist.blogspot.com/2008/05/joe-mcnally-desert-shoot.html

Hit the comments for a lengthy debate on the merits of HSS vs. regular sync and ND filters (the short answer, you don't gain any extra power with pulsed HSS).

Older digital cameras used electronic shutters which don't suffer from the second curtain problem and so can sync up to 1/4000s without pulsing the flash, letting you overpower the sun with a single flash unit. See http://strobist.blogspot.com/2008/01/control-your-world-with-ultra-high-sync.html

edit:

With no extra gear, assuming you have a flash capable of HSS your only option is to get as close as possible with the strobe, light power squares with distance, meaning getting twice as close gives you 4 x the power, getting four times as close gives you 16 times the power! I would start at your base ISO, f/5.6 and walk the shutter speed up until you lose the ambient.

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my whole idea revolves around this "using a high shutter speed you let in the same amount of flash but much less ambient light". i was just thinking if by somehow i can tell camera's sensor dont collect light while opening and closing shutter and set the sync speed and shutter the same (120 of sec) with ISO 100. As flash light is more strong then ambient ones so it will bounce back more quickly so will get the least amount of ambient light around the subject. Result will not be hundred percent black but it should overpower ambient light to some extent. –  Ifi Oct 19 '10 at 19:28
    
In principal you can tell a sensor not so start collecting light until the shutter is fully open, this is how cameras with mixed physical/electronic shutters work. However the 20D doesn't work like this so your ambient conquering options are rather limited. –  Matt Grum Oct 20 '10 at 15:20

Are you sure those sport photos were mixing daylight and flash? For reasons explained by Matt, you'd need to get very close or have powerful flashes to get that effect, which is both unlikely when someone photographs sport events.

IMO there are two situations that might produce sport pics with black background and happen much more often:

  • daylight + shade: what you're looking at isn't powerful flash and full daylight, but actually full daylight and shade (such as dark part of platform). This "selection of background" possible to achieve with long telephotos, and on sunny days the light differences may be several EVs, enough to render background black
  • flash + darkness: what you're looking at is a staged picture taken either when it's dark or in a studio
  • stadium lights + darkness: might make enough difference to make background dark
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Yes I doubt the sports photogs were using any high speed trickery! It's probably just an artifact of using a long lens and the background being in shadow. If it's indoor sports then it's possible the flash is only lighting up the foreground and overpowering the ambient. –  Matt Grum Oct 20 '10 at 15:06

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