Originally posted by ChrisA What I don't get is how 1/250 rather than 1/180 can make all that much of a difference in practice - it's less than half a stop.
Actually it is half a stop.
There are four things you can do to reduce the amount of ambient light in an outdoor photo (ignoring for a moment 'coming back later in the day' as that's not always a viable option)
A) Reduce the ISO
B) Close down the aperture
C) Add an ND filter
D) Increase the shutter speed
When balancing flash and ambient light, choice 'D' is the only one that does not also reduce the flash's contribution, and therefore the only useful option, especially if you are already at full power on your flash.
To increase flash contribution you can:
1) Increase the output
2) Move the flash closer
3) Focus the light by zooming or add a Fresnel-type attachment.
Let's look at these. 1) is a possibility as long as you are not already at full power, but there are drawbacks. At full power the flash takes longer to recycle, even good flashes take as much as 4 seconds, an eternity when action is going on
right now! It also increases the flash duration exponentially, so if your objective is to freeze motion, choice 1 is unacceptable. 2) - Moving the light closer is sometimes possible, but not always. If you're photographing, let's say, dancers outdoors, placing a lighstand close enough to get a good flash/ambient balance may result in injuries to the dancers and/or damage to your equipment. Choice 3) a Fresnel attachment can cause very harsh and unnatural light, and it may not fill your field of view, particularly if the light is already close.
So why not use HSS? Well HSS causes a huge reduction in flash power as soon as you cross the threshold, and it only gets worse from there. It basically reduces the flash's effectiveness by a factor of 4, so if you were at quarter power below 1/180, you're now a full power at 1/250th, not to mention the added problem of long recycle time, and if you were at half power at 1/180th you're now S.O.L. HSS is only useful with a good flash up to about 1/1000th, and then only if you can get the light very close. Add a softbox and you lose a stop of that light so now it's only useful at 1/250th and 1/500th.
You're right though, 1/250th is not all that different from 1/180th, but every little bit helps. Really I think if Pentax would put a 1/500th syncing DSLR out there, even an APS-C, strobists would flock to the brand, even with the antiquated flash system. It's that important to them. But the very best, and surprisingly one of the easiest solutions is what I call a "hybrid shutter", but most folks refer to as an electronic shutter. Such a camera could would really be a feather in Pentax's cap... at least for a year at which point Canon and Nikon would follow suit, unoriginal bastards.