Flash Fall Off

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bumfluff

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Mikey
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I'm pretty new to the art of photography so I hope you can help me. I am trying to take a photo where the flash falls off completely leaving the subject in the foreground and the background completely black. I am currently using a Fuji S6500fd, what conditions would I need to get this to work properly and how would I set up my camera to do this? Although I obviously don't have all the features and modes of big people's cameras.

Thanks
 
You need to know the guide number of the flash to work it out.If you divide the guide number by the f stop used it will give you the distence your flash will work at.
 
Hi bum,

shoot it outside, at night. Set your cam to -1 stop exposure compensation.

Have fun!
 
Flash guide no. 8.3 m (27.2 ft) 3 m
Aperture range F2.8 - F4.9

Thats the information I've found.
 
Don't bother with the numbers.

What you need to do (if you can, I don't know your camera) is set your camera to it's highest sync speed and pick a small aperture. Get your flash close to the subject (this makes the flash less powerful but will expose the subject correctly) and assuming your background is a reasonable distance away the fall off should make the background black.
 
How far away roughly should the background be? Would it be far enough away in normal sized room?
 
Difficult to say really as it's all relative to the distance your flash is from the subject.

Have a look at these three that I shot when I was experimenting and learning how to light (as you can tell by the not so great composition). There's plenty of ambient light in this room, I think all the normal evening lights were on so as you would normally have in your living room in the evening. The setting I used meant that none of that ambient light affected the exposure so all you can see is flash generated light. All were shot at the same settings: ISO 400, f16, 1/250s.

All I have done is move the flash closer to the subject in stages and dialled down the flash accordingly to expose the subject correctly. You can see clearly the effect it's had on the subject.

Buddha-1.jpg


Buddha-2.jpg


Buddha-3.jpg


EDIT - I should just add this was done with off camera flash remotely triggered. It's going to be a lot harder to get this effect using flash on top of your camera as the flash position is then restricted by where you can place your camera.
 
Hope this doesnt sound stupid, but what does it mean to set your camera to its highest flash sync speed? I shot with a canon 400D
 
Not stupid at all, there's a heck of a lot to learn about flash.

The highest flash sync speed is the fastest shutter speed your camera can take a picture at and still ensure the flash is synchronised with the exposure (ignoring special modes which can be faster). My 30D's highest shutter speed with flash is 1/250s and I'd expect your 400D would be the same.
 
bumfluff said:
I'm pretty new to the art of photography so I hope you can help me. I am trying to take a photo where the flash falls off completely leaving the subject in the foreground and the background completely black. I am currently using a Fuji S6500fd, what conditions would I need to get this to work properly and how would I set up my camera to do this? Although I obviously don't have all the features and modes of big people's cameras.

Thanks
Click to expand...

The power of the flash falls off according to the "inverse square law". That means that each time you double the distance to your subject the light becomes only 1/4 the strength at the closer distance. 1/4 is 2 stops.

So, let's say the distance to your subject is 4' and the background is 8' away. The background will be 2 stops darker than your subject. If you can double the distance to the background again, to 16', it will become 4 stops darker than your subject. If your background is no brighter than middle grey it will look pretty dark at that point.

Your simple choices are either to use a dark backdrop in the first place, and/or place the background as distant as you can from the light source, compared to your subject.

As has previously been stated, if you use the fastest shutter speed possible, for your flash, you will minimise the impact of ambient lighting falling on the background (and the subject). If you close the aperture down and pick a low ISO you will make the flash work harder (this is where the guide number is important), but so long as it is powerful enough your subject will be lit correctly and the background should disappear to blackness.

EDIT : I was trying to locate a good reference example, which I've seen before, but yesterday the critical example image was not loading for me. Anyway, the picture that goes with item #3 here - http://photography-on-the.net/forum/showthread.php?t=171657 seems to demonstrate the fall off well. There may be some other useful stuff there as well.
 
Yeah, I know the inverse square law from all my hard work in Physics jsut didn't apply it to the photography. I've had a bit of success anyway, although I haven't played with it too much.
 
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