Guide Number. 190 (at ISO 100, feet) / 58 (meters); flash head at 105mm zoom setting or 45 AF points;Distance range -- 2 to 32.8 feet (0.6 to 10m) at center; 2 to 16.4 feet (0.6 to 5m) at periphery Custom Functions. Fourteen Speedlite Custom Functions built-in; set on Speedlite's LCD panel parts or devices (including, without limitation Flash. PC (Prontor-Compur) terminal and dedicated E-TTL II hot shoe. Built-in flash. Guide Number 12 meters (39 feet) at ISO 100. Covers as wide as a 17mm lens on the 70D (28mm equivalent felid-of-view on full-frame). Flash Sync Speed (maximum shutter speed with flash) 1/250. Shutter. Vertical focal-plane. Self Timer. 2 or 10 seconds. Advance The Olympus FL-300R is an easy-to-operate versatile external flash for your PEN. With an equivalent GN (Guide Number) of 28 at ISO 200, you can accomplish flash shooting with stable light and optimum brightness. It functions as a bounce flash and wireless remote flash with enough power for most any typical shooting situation. Whether the flash is Manual, Auto (thyristor) or TTL doesn't matter. Flash duration is about between 1/400 at full power to 1/20,000 at low power in most on camera flashes. This speed is reversed with most "studio" flashes. (Profoto, Elinchrom, etc.) HSS is a gimmick that greatly reduces output. But you are absolutely correct; Manual flashes The guide number is a means to discuss a flash unit's relative output power. How much light they are capable of throwing into a scene. To compare flash units, it is a presumption that ISO 100 will be used and that feet will be the unit of distance when guide numbers are discussed. Display - The digital meter needs light for activation so you may need to shine a flashlight on it. The display alternates between the meter read and the flow rate. The meter read equals the gallons (or cubic feet) used while the flow rate equals the number of gallons (or cubic feet) per minute flowing through the water meter. Olympus FL-300R Wireless Flash $168.75 More Details Overview Specs Reviews Learn Accessories About Olympus FL-300R Wireless Flash, Guide Number of 20" Meters at ISO 100, 65" Feet Remarkable for a tiny light flash I was surprised to find that the flash was capable of providing as much light as it did. Every flash system has a guide number, or GN. It is used to measure the system's ability to illuminate the subject to be photographed. It's good to know the GN when deciding to buy a flash and how best to use it. The GN represents the output of illumination that is metered at a distance of 1 meter (3 feet) from the subject at ISO 100. Recall that aperture is computed as the quotient of dividing the guide number of your flash by the flash-subject distance. Set the camera to use the calculated aperture. The flash is mounted in a FZ-10 and the flash-subject distance is 6 feet. A flash meter would be very helpful. The flash covering distance ranges from 0.6 to 20m. The corresponding range in feet is 2 to 65ft. SB-24 SPECIFICATIONS Guide number ("Leitzahl") in meters/feet for ISO 100 When you're using other films than ISO 100, multiply the values in the above table with the following factors: Flash angle of coverage Miscelaneous data The OM-4 was the first camera with a built-in multi-spot exposure meter (2% of view; 3.3˚ with 50 mm lens) which could take up to eight spot measurements and average them. (10 meters of film = 250 frames) and the Olympus T-system fl