Originally posted by Culture Why do people complain about the 180 flash sync speed for Pentax compared to Nikon that has 250. I mean the difference is not even half a stop. Can the difference have that much effect on the ambient light during flash photgraphy?
The easiest way to understand the problem is to get out there and try it yourself. Go out on a bright sunny day with a friend, and bring your camera and a HSS capable flash unit. Now, put the sun behind your subject to give a nice glow to the hair, and to keep him/her from squinting. Put your camera in Shutter priority and set, oh 1/4000th as the shutter speed, and take a shot. That's about the shutter speed you'd like to use to get a nice portrait, but obviously you won't get a flash and your friend will be completely backlit.
So now switch over to manual and start stopping down your lens until the point where you can activate your flash. 1/4000th>1/2000th>1/1000th>1/500th>1/250th>1/180th That's 4 and a half stops (1/180th
is half a stop under 1/250th by the way) So if you started at f/1.4, your lovely portrait will now be at an uninspiring f/6.7.
Now that you are at (or below) your max sync speed, you can begin to compress the dynamic range of the scene with a flash and get some blue back into those blown out skies. Unfortunately your lens is at f/6.7 which has reduced your guide number from 50 meters down to 7.5 meters. Now that's at full power, but for reasons that I won't go into (but you can read up on it), you really don't want to shoot at full power if you can help it. You really want to be at quarter power or less. So that brings your working distance down to 3.7 meters. Did you want to add a softbox to make those shadows a little less harsh? That will cost you another stop. Are we done yet? Nope. The light from the flash is cooler than the ambient light, so that will require maybe a 1/2 CTO gel to keep your subject from looking cyanotic, that's another half a stop. So our final working distance is about 2.2 meters, hope you only wanted a headshot.
BUT, you say, there's always High Speed Sync! Well, try it. As soon as you cross the max sync barrier, your guide number drops to about a quarter of the full power of the flash. As you crank your shutter speed higher to cut out more ambient light, more and more light from the flash is wasted bouncing off the ever-widening shutter curtains, and very little actually makes it to the sensor. By the time we get back up to our original 1/4000th, you working distance is about the end of your lens, so hope you brought a macro lens (hey, they're good for portraits... of nose hair)
Ok, so what is the point? Well as you have observed some users complain that Pentax has a slower max sync speed than Canon or Nikon, these folks are also missing the point. The point is that Canon and Nikon's sync speeds
are also too slow, but when trying to balance ambient light,
every stop counts. Ideally there would be no such thing as max sync speed, you'd be able to sync all the way up to the camera's maximum shutter speed. There are some cameras, like the Nikon D70s, that can do that by using a hybrid electronic/mechanical shutter, but there are some problems getting that trick to work with a CMOS sensor. Leaf shutters in lenses would be a good compromise, but there are far too few of those out there and none for the K-mount. Those who say 1/180th should be good enough are obviously not trying to take the same types of images as those who advocate for higher sync speeds.
[edit: Oh, almost forgot, because of Pentax's implementation of HSS, you need a HSS flash attached to the hotshoe. This means that unless you have multiple flashes, you won't be able to stand back with a telephoto lens, you need to be close to the subject. Don't get me started on the Pentax flash system]