Ken Kuzenski , Sep 25, 2005; 08:07 a.m.
James, I don't know the 3500 specifically, and I don't know where to find manuals. But most of those little thyristor Vivitars are pretty simple to use. There will be a selector switch somewhere, with two colors and a position in between. There will be a scale on the back with a sliding gadget and some color indicators. To use the flash, make sure your camera's shutter speed is at or slower than the sync speed. Pick one of the colors on the selector (the position with no color is "manual"--full flash output every time.) Say you've put the selector in the RED spot; look on the back, set the film speed on the sliding gadget, and you'll see what aperture to set your camera to. (If it's NOT suitable, try the OTHER color setting on the front and see what aperture is recommended at THAT setting.) If all is correct, you can now shoot regular on-camera flash at any distance inside the flash's ability to cover, at the pre-set aperture, and the thyristor will shut off the flash output when it's put out enough light for your photo. I'm not good at explaining things, but it's really very simple when you've done it a few times.
One other benefit of these simple thyristor flashes: Say you're outside and your subject is backlit, and there's plenty of light for ambient photography. Pick an aperture one stop smaller than the recommended (making sure it plus your shutter speed are correct for ambient exposure, and making sure the shutter speed is still at or slower than sync speed), and you've now got fill-flash, one stop down! Very very handy!
HTH. --Ken
