Hi Steve,
Glad you got some working cactus triggers in the end!
I'm no expert on using flash and I'm probably stating the obvious but thought it might be of use / interest to make a few comments with some things I've picked up recently (By the way this is using manual flash / camera settings so I don't know if everything is still applicable to ETTL and other camera modes) ...
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Originally Posted by stevegreen I think maybe a slight adjustment on the flash power would have sorted that. |
You can also adjust the brightness by moving the flash towards / away from the subject as the brightness of the flash falls off as it moves further away from the subject. This will also cause the shadows to be softer / harder as this depends on apparrent size of the light source as seen by the subject. E.g. the sun which is a massive light source casts hard shadows here as it is far away so the apparrent light size is small.
The affect of distance on flash brightness was most noticeable to me when trying to evenly light a wall in the background. E.g. if the flash is just out of frame on the left and aimed so it is firing across the surface of the wall, then the wall is brighter on the left than it is on the right. To get round this you can move the flash head quite far to the left and increase the flash power as required. This means that the difference in distance between the flash / left wall edge and flash / right wall edge is relatively small and so the light fall off isn't as apparent.
I seem to be going off on a tangent but another "aha" moment was when I learnt that the centre of the flash is more powerful than the edge. E.g. if you're lighting a group of people from one side then the people nearer the flash would be lit more brightly than the people further away. You could do as described above for lighting the wall evenly, or you could aim the centre of the flash at the people further away so that the people nearer the flash are light by light coming from the edge of the flash. This way the light fall of due to distance counteracts the light brightness from the centre / edge of the flash so you end up with evenly lit people. I think this is called feathering the light.
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Originally Posted by stevegreen Not easy when you have flash power, flash position, aperture and shutter speed to contend with........it's a massive amount of settings to try and get right when you have no idea what you are doing and why  |
There is definitely lots to think about! I've found it helpful to think of the photograph as a balance between the ambient and the flash. Controlling these two things comes down to two rules:
1. Ambient light is affected by both the aperture and shutter speed.
2. Flash light is only affected by the aperture.
If you want to adjust only how bright the ambient is you can change the shutter speed.
If you want to only adjust how bright the flash is you can adjust the aperture and then change the shutter speed by the same number of stops in the opposite direction to bring the ambient back to where you started. This saves having to walk between the camera and flash to adjust flash power as you arrow in on the ambient / flash balance that you're looking for.
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Originally Posted by stevegreen I had to PM Scott about that shot as I couldn't understand how he managed to get the shutter so fast |
I don't know anything about Nikon kit nor the 5D for that matter, but thought that I would mention a little about high speed sync on the 580. Ignoring the cactus triggers for the moment, if the 580 is on your 5D hotshoe then I think you may be limited to a sync speed of 1/200th. You can overcome this by enabling high speed sync. This allows you to use quicker shutter speeds by firing the flash multiple times as the slit between the first and second curtain travels over your sensor, so you end up with a correctly exposed image. Quicker shutter speeds allow you to overpower the bright ambient conditions or even when shooting directly into the sun as with Scott's photograph.
If you take the 580 off camera and fire it by the cactus triggers you could well still be limited to quite short shutter slow shutter speeds (E.g. 1/200th). The camera doesn't know you're firing a flash so will allow you to select say 1/1000th but you could find that none or only a small portion of your sensor was exposed to the flash so you get unpredictable results.
I agree, it's all good fun! I'm looking forward to hearing about what you've learned over the coming weeks.
Cheers.