The Canon Speedlite 133D is specifically designed for adding Canon Auto Tuning (CAT), the manufacturer�s patented automatic flash system, to compatible cameras. This particular unit delivers the speed and stability photographers demand in rigorous, low-light shooting environments. The CAT system is reputed for providing the lighting benefits of electronic flash, meaning adjusting exposure so nighttime photos have a similar clarity as those taken during the day, while offsetting battery consumption issues and other known limitations. With a remarkably efficient electronic circuit onboard, this Canon ring light/macro flash makes optimal use of battery power and, when set in the manual position, does not light up until the capacitor has a full charge. This ensures that under exposure is not a problem. The Canon Speedlite 133D offers brief recycle intervals so flash photographers can reload in a hurry, while the build of the ring light makes for a unit that sufficiently distributes the necessary quantity and quality of marginal light. Although this automatic flash is designed for exclusive use in the CAT system, it works with a variety of other lenses, including the EF, Ftb, and F-1. In fact, connecting the Canon ring light/macro flash to a different body is as simple as switching it to the manual position. Easy to use, versatile, and extremely powerful, the Canon Speedlite 133D is a comprehensive flash photography system that makes a nice companion for a range of shooting projects.