When another brand's flash is attached to the Nikon D90, the zigzag icon on the camera's display will blink as a warning that the flash must be set to manual mode.
Any flash that uses a hotshoe mount, such one manufactured by Olympus, can be attached to Nikon's D90 digital SLR camera. However, the flash will only work in manual mode.
How Flashes Communicate
Flashes made for SLR cameras send data to the camera by electrodes that connect when the flash is mounted via the accessory shoe.
TTL vs. Manual Mode
Communication via those electrodes is key for through the lens (TTL) metering, which means the flash uses the camera's light meter to determine how much light is needed for the image. In manual mode, the photographer must set the flash's distance and output manually.
Because each camera manufacturer uses a unique electric signal to communication with external devices such as flashes, an Olympus flash cannot communicate with the Nikon camera well enough to use TTL mode.
Flashes Recommended For the D90
Nikon recommends only connecting Nikon accessories to its cameras. Specific flash units recommended are the Nikon Speedlight SB-900, SB-800, SB-600 and SB-400 and SB-R200 and the wireless Speedlight Commander SU-800.
Tags: attached Nikon, manual mode, mode Flashes
