Portable Lighting – The Cone Macro Flash Concentrator

After getting the digital SLR, I ran into a small problem with the light: the slave flashes that I’d been using previously did not play well with the Canon 10D on-camera flash. Specifically, I couldn’t find a way to force the flash to only fire once for a photo. The best I could find was a button that would let me fire the pre-flash, and then have up to 15 seconds to take the picture on the second flash. This was incredibly aggravating, and I wanted something better.

After looking into the preferred methods of insect macrophotographers, the recommendation was to get a good macro flash unit. In particular, people with Canon gear have said good things about the capabilities of the Canon Macro Twin Lite MT-24EX. Then I looked at the price.

“Suggested Retail Price: $829.99

Holy Cow! That’s almost four times what I paid for the camera body! Ouch! And they don’t seem to be very available on the used market, either.

The next-most-recommended option was the Canon Macro Ring Lite MR-14EX. That one is cheaper . . . I guess . . . although $549.99 is still COMPLETELY OUTRAGEOUS! FOR CRYING OUT LOUD, IT’S A FLASHLAMP NOT THE LBNL ADVANCED LIGHT SOURCE! rather more than I really want to spend. Even used ones are still pretty pricey.

So, it was time for a serious rethink: the fundamental problem is to illuminate a small object, quite close to the camera, with light that is simultaneously very bright (to allow fast shutter speeds with a small lens aperture) and diffuse (to both fill in shadows and avoid specular reflections). Having this light actually electronically controlled by the camera is a big plus. Both of the expensive flash solutions above are basically approaching the problem the same way: put multiple light sources practically on top of the subject, blast the entire area with huge amounts of light from several directions at once, and hope for the best. But, aside from the cost of the flash units, I don’t really care for the fact that this also takes a lot of power, which means a lot more fiddling around with batteries just so I can spray more light around in irrelevant directions.

But, consider: I already had a flash on the camera. It was pretty bright, too. Quite sufficient for lighting up an entire room, in fact. It was certainly capable of providing enough light to adequately expose a volume of a few cubic centimeters that happened to have a bug in it. It’s just that the light was coming from the wrong direction for macro work. Most of the light generated never came anywhere near where I wanted it, as shown here:

And, the light that did hit the subject reflected straight back, making bright reflections off of any shiny surface and shadows elsewhere. And for extreme macro, the subject was so close to the camera that the lens would get in the way of the flash. But . . . What if we came up with a way to redirect the light so that, instead of the flash being a point source spraying photons all over the room, the light from the flash was captured and concentrated where we want it?

Hmmmm.[6] At this point, I realized that something I had played with years ago might be applicable here – a non-imaging light concentrator.

The basic idea of a non-imaging light concentrator is that if you just want bright light in a particular spot and don’t care about making the light form an optical image, you can design a reflector that will accept light from multiple directions, and concentrate it into the desired volume. The concentrated light then illuminates any subject in that spot from all sides, making a very bright yet diffuse light. This idea has already been used for concentrating sunlight for solar power applications, but as far as I can see nobody has applied it to photography. So, how about if I design one that will catch most of the light from my on-camera flash, and direct the bulk of it into the relatively small volume that I actually want to illuminate?

While an ideal light concentrator is made from mirrored compound parabolic surfaces, for my purposes we can do pretty well with just a white cone. If the cone is set so that light from the flash goes into the large end, the light that reflects off of the cone wall will end up concentrated in the volume at the small end, changing the distribution of the light to this:

So, what I ended up making was this:

– a wooden yardstick ($0.79),
– a sheet of posterboard (also $0.79),
– a 1/4-20 thread screw ($1.00 for a capscrew, or $2.50 for a clamping knob which is a bit nicer to work with),
– a snap ring to keep the screw from falling out of the ruler ($0.49),
– a piece of adhesive-backed craft foam ($3.00, but only because I had to buy a whole pack to get the thin strip that I wanted),
– and some packing tape to hold it all together (maybe a couple of cents).
Total materials cost was therefore on the order of $6, with two-thirds of the yardstick, 3/4 of the posterboard, and a whole bunch of adhesive-backed foam left over afterwards to use for other things.

– First, measure how far it is from your camera to the closest focus point you want to use.
– Then cut your yardstick to be long enough to go from the camera’s tripod-mounting hole to just short of that focus point.
– Drill a 1/4 inch hole in the yardstick piece, and put in your 1/4-20 capscrew.
– Put the snap ring onto the capscrew to keep it from falling out of the yardstick piece.
– Cut a piece of adhesive foam to put onto the yardstick, make a hole so that the capscrew can go through it. This will make a base for the camera to sit on without wiggling.
– Cut an arc out of the posterboard, like so (measurements are approximate, and were mainly chosen for convenience):

– Roll the posterboard arc into a cone so that the large end is about 7 inches in diameter, and the small end is about 5 inches. Tape it to keep it from unrolling.
– Tape the cone to the piece of yardstick so that the small end of the cone lines up with the tip of the yardstick piece.
– Fasten it to your camera by screwing the capscrew into the camera’s tripod mount threads, and you’re done! If necessary, use scissors to trim the cone so that you can reach the controls of your specific camera better.

And here is the resulting flash concentrator cone:

Cone for standard macro lens

I then made a second one for higher-magnification macro photography, where I screwed on an additional magnifier and the subject was only an inch or two in front of the lens:

Cone for close-focus macro lens

In both cases, the cone was cut so that I could still turn the focusing ring on the lens. The tip of the cone in each case was about an inch short of where the object being photographed sat.

So, what difference does it make? First, let’s look at an adult cricket (a dead one, to avoid being distracted by chasing a cricket around), using the 100 mm lens at 1:1 magnification with the lens aperture set at minimum size (f/32) to give the greatest depth of field (without the concentrator, it wasn’t practical to choke the aperture down this small because there wasn’t enough light to keep the shutter speed fast). First we’ll look at it without the flash cone, and then compare with the identical camera settings with the flash cone:

Adult without flash concentration

Adult with flash concentration

As you can see, with the cone the whole image was markedly brighter, shadows were mostly filled in, and it was generally much easier to see detail. Now, let’s look at a cricket nymph using the higher magnification setup (a reversed 50 mm lens mounted on the end of the 100 mm lens. This looks to give a magnification of about 2:1, which is more of an increase in magnification than it sounds like). Again, the camera settings were identical in each case:

Nymph without flash concentration

Nymph with flash concentration

Here, we see that the flash concentrator again made a huge difference. Without it, the subject was dark and practically indistinguishable from the background. But with it, the cricket nymph was uniformly illuminated with all features clearly visible.

Overall, the effect is similar to using a “White Box“, except instead of being an immobile stage, it is a portable thing attached directly to the camera, making it easy to use in the field. The flash concentrator cone is a bit bulky, but no more so than the supplemental flash units that would be needed otherwise. And best of all, it is

    – Cheap;
    – Easy to make;
    – Cheap;
    – Pretty rugged;
    – Applicable to most cameras with a built-in flash;
    – Did I mention Cheap?

While I’m sure that the expensive flash solutions can do a number of things that the flash cone can’t (at those prices, they had better!), the cone still goes a long, long way towards solving my long-running lighting problems. So, go ahead and try it out, and if any of you develop further refinements, please let me know.

3 Responses leave one →
  1. Victor Hugo Neumann permalink
    April 26, 2012

    Thanks a lot! It’s refreshing to see simple, elegant and CHEAP solutions.

  2. May 4, 2012

    Thanks! I’m working on a Mark II that won’t be any more expensive, but should make it easier to get at the lens while eliminating some distracting lighting artifacts. More details as things progress.

  3. September 13, 2012

    There are so many ideas like this – that before the Internet – never saw the light of day – because someone could not make a buck off it since people could make it themselves. Thanks for sharing a very clever idea and solution. Bravo! I wonder how many great ideas have been lost to history due to an all powerful profit motive. With the free interchange of ideas – more new and creative ideas spring forth.

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