Originally posted by chromo I never thought about the K-5 still doing pre-flash in standard mode.
The
only way for Pentax DSLRs' built-in flash NOT to fire a pre-flash strobe is to use a manual lens. In this case, the built-in flash fires one strobe at full power. If you plan to use optical slaves, the slaves have to either support p-TTL mode, or be able to ignore the preflash strobe. There are some optical slaves that can ignore the preflash strobe. But RF remote trigger is much more convenient.
As you mentioned, a way to get around this is to use an external flash in non p-TTL mode, attached to the camera's hotshoe.
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Edited to add: Originally posted by chromo Is it safe to put that AF 160 on my K-5 ? and are the YN-560's safe too ?
I know the AF160 is safe, using one myself. I think the YN-560 is safe.
About trigger voltage, you should learn how to measure it. A flash model may have many versions, with different trigger voltage.