Ring Flash, Around the Lens Or Around The Subject :)
Published by easymovet on Monday, November 12, 2007 at 16:22
Get the flash off the camera, even a ring flash!!!
The Ring Flash / Ring Light is a unique light source since it gives you a hard light but because the light comes from all around the lens the only shadow is a darkened halo around a subject, but the subject it self is uniformly lit.
My favorite effect of a ring light is the ring in the eyes and the topographical effect of the highlights it creates on the face, normally a head on light source would flatten a face but the ring flash makes highlights on relief areas of the subject. I fell in love with the effect in this image by Janosch Simon
(this images is SFW but his full portfolio may not be if you live in the US)
Creating a ring flash can either be done with expensive flash units that are actually capable of a circular arc in a circular flash tube/bulb, or by modifying the straight round beam of a hot shoe flash unit.
There seems to be two ways to go about it, diffuse the source then mask it, or use precise reflections to redirect the beam. The second would result in higher efficiency and a higher "focal length" of the flash since there would be more direct light.
In order to control the size of the ring on the face you have to change the distance of the ring or the size of the ring. Having it off camera would allow you to take telephoto shots and still have large ring in the eyes ( a telephoto shot with a tradition on camera ring flash would be far away enough to reduce the reflection of the flash in the eyes to a bright dot)
What i did was adapt this great design by 
The Feral Photographer and made the following changes.
1:made the circles NOT concentric, the light escaping from the diffuser causes the light level to get dimmer at the end opposite the flash, similar to , here it comes, the inverse square law. So i sized and located the inner circle to so that the distance at the far end was four times less than the flash end this would result in a uniform distribution of the light.
2: Made it larger, this means that i could use longer zoom.
Materials:
2 sheets of cardboard
mylar/tin foil
Tape, Knife
Diffuser material is a Target plastic bag
Final Effect:
click image for super hi-res image (copyright yo)
So Alexander Johnson took my image and had is skilled way with it creating this image:
Post Processing by Alexander Johnson - Thanks!
learn to light on strobist
Could you please elaborate on what you mean by making inner circle non-concentric and what distance is less at far end than at flash end? I think you are on to something, but can't visualize the construction.
A few photos of the work in progress or details would be very helpfull indeed. It's hard to visualize everything you say.
Thanks already
hey i did a re-edit of the photograph of the model using your ringlight, if you would like me to send it to you, send me a message at www.flickr.com/photos/apjohnson
Thanks for the clarifications. However, I don't quite buy the explanation about inverse square law and 1:4 ratio of distance between inner and outer circle.
Why would placing the inner circle closer to the outer circle make that part brighter, and placing it further make it darker?
I would have thought that making the far end narrow just limits the amount of light that can reach the far end of the ring.
mtreinik: Thanks for the great question! Think of it like a hose of water when you pinch it the water travels farther. Think of the percentage of "leakage" out of the amount of available light, at the thick side there is lots of light so we only want to "leak" a small percent, at the far end the diffuser accounts more like a quarter of the internal reflection area so more of the internally reflected light in that area will be leaked. Look at the model i based it after which has concentric circles, it is very clearly non uniform, whereas mine is perfectly uniform, not the least bit dimmer at the far end.
Again thanks for your interest!
thats cool riaz, but how did you get it to turn on right when you took the picture? soooo cooooool. and have you ever thought about using something other than cardboard...so many materials in the world.....
Hello,
I see that you got the result right, but I still don't understand the math behind it.
I understand the rule of energy dissipation power/distance, that's OK. But why did it work on this way here? The light is not dissipating in a simple way like the link you posted. I suspect there are some more complex math behind it, do you have any idea?
I would like to understand it so I can build a similar one :)
I will put some more thought on it too, will post again if I find something.
Thanks!