Articles

   Replacement Battery for Yashica Rangefinders
(April-2010)

   Battery testing on Canon film cameras
(March-2008)

   LED Ring Light
(A cheap alternative December-2006)

   LED Lamp
(January-2011)

LED Ring Light

Back when I started using eBay to sell stuff, I suddenly needed something I didn't have - good closeup lighting. Commercial ring lights for the part-time user are way overpriced. Professionals can afford them but what about the rest of us? The answer is to build my own.

Digital photography offers a big advantage over film - the instantaneous feedback of exposure. What this means is that for my ring light, I don't need fancy flash control. I just need a device that can light the scene, and let the camera's meter handle the rest. If the exposure looks bad, simply re-shoot.

My LED ring light consists of two parts - a ring portion that screws onto the filter ring of a lens and the battery portion.

The battery section is very simple. I started with a simple audio cable and cut it into a long section and a short section. The long section goes with the battery. A 9v battery clip is soldered to the cable on one end and a female RCA connector is soldered onto the other end. That's it. The picture below shows the result.

The short cable is used to provide power to the ring light LEDs. To get enough light, I used high brightness white LEDs. Mine came from an eBay seller from Hong Kong but you can find them at domestic suppliers as well. I bought a pack of 50 LEDs for $10.99 (includes overseas s&h). These are small (3mm) devices and are rated at 16000 mcd output with a color temperature of ~7000K. Forward voltage drop is about 3.3v at 20mA. Note that these are 2005 prices.

To hold the LEDs, I used a step-up 58-to-77mm filter ring ($7 with s&h). 58mm happens to be the filter size of the lens I'm using. The size difference to 77mm give me enough space to mount the LEDs. I used 16 LEDs though I had enough space for more. For each LED, I drilled a small hole and glued the LED with some epoxy. I also had to add some current limiting resistors. Since I'm using a 9v batttery for power, I can use one resistor for every two LEDs and save some room on the step-up adapter. Each pair of LEDs is wired in series (being careful to observe polarity) with a 100 ohm resistor. All 8 pairs are then wired in parallel. The combined power draw is about 160mA and that comes from the short cable which terminates in a male RCA connector. Below are pictures of the front and back of the ring.

I used a lot of epoxy to make sure the heat shrink tubing and wiring do not move even when bumped. The epoxy also helps to stiffen the area where the cable meets the ring since that will have the most stress in actual use.

There is no on-off switch. To use, screw the ring onto the lens and connect the 2 cable ends. Keeping the short end short makes it a lot easier to screw onto the lens. The cable can be an annoyance especially if the lens has a rotating filter ring during focusing. The rotation will drag the cord around in a circle. I typically do not screw the unit on all the way. This gives me some play with which to rotate the ring light thus letting the cable hang at whatever spot is convenient. Below is a picture of the unit powered up.

03-January-2010


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