Is there any disadvantage using the highest possible flash sync speed all the time? That is, leaving the flash sync setting at 1/320s (AutoFP) even when using a slower shutter speed?
Here are my concerns: I have D700 (Nikon) and it's default value for flash sync is
1/250s, while there's an option
1/320s (Auto FP).
The manual says:
1/320s (Auto FP)
Use auto FP high-speed sync with SB-900, SB-800, SB-600, and SB-R200 flash units. If other flash units are used, shutter speed is set to 1/320 s.
SB-700 and it seems to work fine with this option. Also, this seems to work fine with the built-in flash of D700.
One more interesting quote is:
When 1/320 s (Auto FP) is selected for Custom Setting e1 (Flash sync speed, pg. 305), the built-in flash and optional SB-900, SB-800, SB-600, and SB-R200 flash units can be used at shutter speeds as fast as 1/320 s; at faster speeds, Auto FP High-Speed Sync is available with optional SB-900, SB-800, SB-600, and SB-R200 flash units.
(I think SB-700 is not mentioned, because it's a newer model from D700, if I'm not wrong).
So, why would I choose 1/250 (fixed; the default one) or less, instead of always using
1/320 (Auto FP)? Or maybe this
Auto FP is something that I don't understand?
P.S. I'm talking about standard usage of the flash, using TTL, no front/read curtain, no more external flashes, etc.
EDIT just to be clear - I don't mean, that when I choose
1/250 (Auto FP) (or similar), I'll choose the same shutter speed. For example, if I may use 1/60 as shutter speed, combined with
1/250 (Auto FP) sync speed. And this should be fine, right?