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02-24-2015, 06:23 PM   #1
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Vivitar 2800 with a K-50

Got a nice new K-50 for Christmas from my parents. I wanted this model specifically because its weather resistant and Dad had a pentax SLR when he was in high school. He had a lot of accessories for it. He has a couple of external flashes that I am trying to get working. Specifically, a Vivitar 2800 Auto thyristor model. I realize that the trigger voltage is too high for my camera, so I built the following adapter > circuits > optoisolated adapter l35316 -, and stuffed it in the base of the flash. It seems to work as when I press the red manual fire button (it ties the hot shoe lines together before the adapter), it fires no problem. What I'm wondering is how do I set up my K-50 to use this flash? I've looked around, and I haven't seen any good way to use a manual flash with this model.

02-24-2015, 09:48 PM   #2
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Does it also fire when you short the center pin on the flash?

Easiest modes to use are Av and M (on the camera). For Av, set aperture and ISO, adjust the flash to reflect those settings and fire away. The camera will adjust the shutter speed and will try to achieve a normal exposure as without flash.
For M, it's basically the same; you have the option to adjust the shutter speed to influence the effect of the ambient light; longer shutter speeds will let more ambient light in; iit will not effect the amount of flash as the flash duration is usually far shorter than the shutter speed (1/200 .. 1/20000 sec)

Note that the camera will not trigger the flash if the selected shutter speed is faster than 1/180s (so e.g. 1/90 is fine but 1/250 is not).
02-24-2015, 11:01 PM   #3
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The manual for your flash is available on the Butkus site:

Your flash will operate at full power (M position of switch on front) or low power auto-thyristor (blue position) or high power auto-thyristor. In red or blue mode set aperture according to ISO using the slide calculator on the back. In those modes the flash duration will be determined by the light sensor on the front of the flash. In full power mode, the aperture is determined using the slide calculator and distance to subject.

Use M mode with shutter speed at 1/180s or slower.


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