Under-exposure using flash with K-m

My wife was trying out my (our!) new flash on her K-m last night, and all the shots were under-exposed by about one and a half stops, even with +1 dialled in on the flash, and we also tried +1ev on the camera. The under exposure occurs using TTL or bouncing it off the ceiling. It exposes perfectly when attached to my K7. Her camera uses 1/45th second and mine 1/180 with the flash attached, I don't undersdtand why they use different shutter speeds, or if this is in some way part of the problem? I'm pretty new to flash photography, any advice appreciated. The flash is a Tumax DPT386AFZ.

Apart from this I am very happy with the flash, and my entry for the weekly competition was taken with this and a home-made soft box I knocked up yesterday from a plastic container, some tin-foil, and the translucent material the flash was wrapped in!

I know the K-m flash sync speed is 1/180, so I usually set it to that (manually), set the aperture to what the flash expects, then use the Auto mode on the flash to set the exposure. No trouble so far. Mind you, it also seems to work fine if I use an old Pentax AF240Z with both camera and flash set to "P" - it generally shoots at around 1/45 and f8 or so depending on ISO setting.

1/180 is actually the maximum sync speed so any speed longer than that can be used. Are both your cameras using the same ISO? Best not to leave that setting on auto IMO.

The different shutter speeds will make no difference unless you are using manual or P-TTL. Does your flash support P-TTL?

Ahh, ok, that would explain a lot!

My knowledge of using flash came from a K1000 where you just set the shutter speed to "X" (aka 1/60 on that model). Oddly enough I couldn't find any reference to what speed equated to "X" on the K-m, but the Dimitrov site quoted 1/180 which seems ok with my Metz 45.

Max sync speed so X isn't connected to the flash but with the speed the shutter moves, the faster it moves the faster the max sync speed can be.

Both cameras are set to 200 ISO, using Av, but the K-m sets itself to 1/45 and the K7 to 1/180. All the settings are identical, yet the K-m under-exposes.

1/45 versus 1/180 should not make (much of) a difference with flash (if flash is the main source of light). The difference in shutter speeds is probably caused by a difference in p-ttl implementation in both cameras.

The difference in exposure is also caused by a difference in p-ttl implementation in both cameras (not necessarily the same difference).