Throw Your Strobe To Great Lengths Using a Poor Man's Better Beamer
It is not really possible to defy the inverse square law. I know I tried and failed miserably. But you can stretch it.
A better beamer is a device that does just that, it extend the distance the light from your strobe travels. So while the inverse square law is still in effect, it stretches over a greater distance.
Physics bla-bla aside, it means that light coming from your strobe will go further. Some strobes, like the SB900 has an impressive zoom functions that does just that.
Flickr used lonelyhome contrapted a poorman's better beamer using a cheapo Fresnel lens (around $1) and some plastic (I assume cardboard will do too).
The picture is really self explanatory.
and the test shows that it actually works improving exposure by 1 stop over distance
If you are out there planning to shoot far away birds, this may be just the stop that is missing
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Comments
Is it really Better?
I am trying to comprehend how this improves the projection distance of the light source. If I applied this logic to my car headlight beams would they not still reach the same distance? All this attachment seems to do to me is create a snoot effect?
It doesn’t make the light
It doesn’t make the light go further (that would be silly!), it collimates the light into a tighter beam. Superficially it is similar to putting a snoot on but the big difference is that rather than wasting the light not going in the right direction, as a snoot would, the lens bends the light so it is all headed in the right direction. See the two photos above? With a snoot the brightness at the centre would be the same, just the fall off towards the edges would be sharper. With the right photo it is clear that the centre is much brighter, about a stop according to the commentator, that’s a fair bit. Depending on how good the focussing is the comparison will be more favourable the further you are away.
Generally, when you are using
Generally, when you are using it, you are zoomed in to the point where you don't see the darkness around the sides, that was just there to show the concentration. PLus it usually isn't that bright, because it is used for fill flash for the most part. If it was used for more than fill, you get the evil shadows. I have it, and use it here and there. I used it more when I didn't have a sb-900! :-D
The fresnel lens focuses the beam
In response to Litte Rock Photo:
The extra range/stop is achieved by focusing the flash beam more compactly. Notice that the spot in middle is brighter but the area outside is darker. Light that would have spread out over a wider area is now concentrated into the center.
Thank you for explaining! I
Thank you for explaining! I understand the prism concept. Would it improve any with the top and bottom sealed to better bend those escaping photons? Not trying to be an arse here, I just want to learn and improve my understanding from the post. Thank you for the feedback!
Probably not much
You could seal it all around and line with reflective material. The improvement from this would depend on two things:
1. The fraction of flash light not going through the fresnel lens (but instead going off to the side or bouncing off the lens).
2. The ability of the lens to send off-angle light (from reflections off the side) out straight toward the target.
I suspect the answer to 1 is no more than 10 or 15%. And I suspect the answer to 2 is "not very good'. Since things are logarithmic (100% more light for 1 stop), I doubt whether you would gain enough to make much difference. But one could wrap some foil around it and do a quick test to see.
Question
So where do you find the cheapo fresnel lens that goes on the front?
@ Little Rock Photo
Most of the higher end flashes already have lenses like this in the flash head so it can "zoom" the flash as your lens zooms in or out. This is just extending the concept further to get even more distance by adding an external lens. If make this project and your flash does have zooming capability make sure to set it to the furthest zoom so as much of the light is focused onto the fresnel lens as possible.
@James
Thank you! I will read up on it more. As an available-light shooter I like learning from this sites users experiences.
WARNING!!!!
Do not accidentally or on purpose, point it towards the sun...it acts in reverse and the sunlight will melt your very expensive flash, lens hoods, etc. in less time than you can imagine. Think magnifying glass and ants on the sidewalk.
Last year, I lost a lens hood...I kept smelling burning plstic and couldn't figure out where it was coming from...I found out later...lots of meted plastic teardrops all over the side of the hood where the BBeamer was. It is mentioned in BBeamer's documentation, but not here.
This could work too...
I forgot about an instructable I had written up a few years ago for a small light diffuser, in the comments one user suggested making a "better beamer" using the same design but replacing the diffusion panel with a cheap fresnel lens. http://www.instructables.com/id/Yet-Another-Flash-Diffuser-designed-for-...
Anyone know where you can get that black plastic in larger sheets? I've had so many other ideas using this stuff but I need bigger sheets than a duotang or file folder provides.
plastic sheets
Try interstateplastics.com . They should be able to take care of you.
Distance from flash
Does anyone know if the distance the fresnal lens is placed from the flash will make any differene, and if so what is the ideal range?
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