Originally posted by TimKierath Hello, just trying to work out what options there are for a flash that fires faster than the "limit" of 1/180.
I thought that the Yongnuo radio triggers would help me out even with a "dumb" flash but it seems I'm still capped at 1/180. So far I've worked out: the genuine Pentax flashes of course (AF540, AF360), the Sigma supers... which are hard to find and a bit expensive considering they don't get good reviews. are those my only options?!
What is your subject, what are the ambient lighting conditions, and what are you trying to achieve with your image?
There are primarily two types of mechanical camera shutters - focal plane and leaf shutters. SLRs with interchangeable lenses, with rare exceptions, use focal plane shutters. Focal plane shutters are the size of the sensor and therefore have much more mass than leaf shutters which are typically mounted inside the lens itself.
Focal plane shutters also have two shutters (leading and trailing) each of which move at a constant speed no matter what the shutter speed is for the exposure. Variable shutter speed is achieved by changing the timing between the two shutters. For shutter speeds higher than the fixed curtain speed, exposure is achieved via a moving slit. Since the Pentax shutter takes 1/180th of a second to cross the sensor, that is the highest speed at which the entire sensor is exposed to light at the same instant.
High speed sync (HSS) flash strobes the flash at shutter speeds higher than 1/180th second as the slit moves across the sensor - but because the actual duration of the total exposure is always 1/180th second, HSS is typically a poor choice for capturing motion. Usually it is better at balancing flash lighting with very bright ambient lighting.
To do high speed motion photography, like catching a drop of water hitting the surface, the best technique is to use very dim ambient light so that the exposure is mostly controlled by the duration of the flash rather than the camera's shutter speed.