2026-06-19 Vivitar Auto Thyristor 550FD Flash

The Vivitar Auto Thyristor 550FD is a dedicated flash that supports TTL. It's closely related to the Vivitar 2800-D family of flashes - the body is almost identical, but this flash has an additional TTL mode. The F might be for the Four operating modes.
My manual says "Printed in 1984", which sounds about right. Vivitar sold them for quite awhile, but keep in mind that this is an early 1980s design.

The "D" in the name means that it is a dedicated flash for, on this flash, Nikon cameras. By "dedicated", it means the flash tells the camera when it is charged, via a Ready pin on the hotshoe. That is all. The flash does not set the shutter speed or f-stop. The body may detect the "ready" signal and select the shutter speed, but this depends on the camera body, not the flash.

TTL mode: this is not P-TTL. This is the 1980s TTL, which required a sensor in the camera body. When the sensor got enough light, the camera told the flash to shut off. With any later DSLR, or earlier lenses, you should use Auto or Manual modes on the flash and manual mode on the body.
Auto mode (A1 or A2): the flash has a built in sensor that will shut off when it feels the scene has enough light. A1 is for "far" subjects, and A2 is for "near". There is a table on the back of the flash to determine the correct aperture for a given mode and ISO (assuming shutter is set to the camera's flash sync speed). The camera has to be manually set to match the table. Changing the ISO slider on the flash just adjusts the table display - it does NOT communicate anything to the camera.

Manual mode: Full power only. Use the table to figure out your shutter/aperture/ISO settings and set them manually on the camera using M-Manual mode. You can reduce the output by pointing the bounce head upwards, using a diffuser, etc.

The guide number at ISO 100 is 24 meters or 80 feet (meaning at full power, ISO 100, and subject at 6m/20ft, set aperture to f/4). The trigger voltage on every unit I've checked was 4 volts, which is safe for DSLRs. You may want to check first, just to be safe.
There are many, many more powerful or sophisticated flashes out there, but if you want to shoot "old-school" with something cheap, reliable, and fairly compact, the 550FD is a pretty decent flash - look how many still work after all these years. Most of the ones that don't work just need to have the contacts on the battery door cleaned (these things ate alkaline batteries, which then usually leaked). You can easily find one for less than ten dollars, or even 99 cents if you shop carefully.

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