Flash sync speed question (Re-post)

Hi!
I'm afraid I don' t get the idea of flash sync. What does it mean to set a camera to a certain sync speed and why do I have to do that? On my Oly E-330 I set it to 160th of a second, but more because I felt I should set it to something rather than because I knew what I was doing. Now I have noticed that when I shoot on land, it won't let me choose the shutter speed anymore when I set it to "Fire flash" - it is locked at 160. I guess my question is three-fold:
1) Do I need to set my cam to a flash sync speed for uw photo?
2) What is it good for?
3) What should I set it to? (I'm using two DS-51s)

Setting your shutter speed syncs the shutter curtain with the flash. many years ago I neglected to verify I set the shutter speed correcty.(1/60th of a sec. for this camera) and happily shot a complete roll of christmas pictures, only to be disapointed when the roll was developed and found half the frame did not get exposed. On land I assume your flash is communicating with the camera via the hot shoe and it sets shutter speed automatically. I doubt your underwater strobes communicate with the camera the same way, so manually setting the shutter speed to 1/60th of a second ensures propper shutter sync.

pteranodon:

Hi!
I'm afraid I don' t get the idea of flash sync. What does it mean to set a camera to a certain sync speed and why do I have to do that? On my Oly E-330 I set it to 160th of a second, but more because I felt I should set it to something rather than because I knew what I was doing. Now I have noticed that when I shoot on land, it won't let me choose the shutter speed anymore when I set it to "Fire flash" - it is locked at 160. I guess my question is three-fold:
1) Do I need to set my cam to a flash sync speed for uw photo?
2) What is it good for?
3) What should I set it to? (I'm using two DS-51s)

Click to expand...

Let's start at the beginning. A "synch speed" is any shutter speed where the shutter will be completely open for the entire duration of the flash. All cameras have a maximum synch speed, which is the fastest shutter speed during which the shutter will be completely open for the entire duration of the flash. Any shutter speed set at or slower than the max synch speed will result in photos that have received the entire flash exposure. Different cameras have different max synch speeds. In the old days, 1/60 was pretty much the standard max synch speed, but modern cameras often have max synch of 1/250 or faster. From your post, it seems as if your camera's max speed is 1/160. For flash photography, you must set your shutter speed at 1/160 or any slower speed. Most modern cameras (including yours, it seems) will not allow you to set a shutter speed faster than max synch if the camera detects a flash.

What is it good for? Well, max synch speed is a limitation on the shutter speeds you can use to get a full flash exposure, so you could say that it's good for nothing.

You should set your shutter speed to whatever speed will give you the exposure you want, but realize that exceeding the max synch speed when using a strobe will result in photos that are only partially lit by the strobe. The advantage of faster max synch speeds is the ability to cut ambient light with a high shutter speed and allow the strobe(s) to light more of the subject. -Clay