flash sync shutter speed confusion

[negative_optimist]

I've gone out and bought myself a Nikon 700 speed light as a start into flash photography. Flash has always confused me since trying to use one with an old film SLR and since then I kept away. My current problem is actually understanding how to use this with my D90. I'm familar with the sync shutter speed. My old film camera was 100th of a sec and that was simple. The D90 acts like it's unsure and restricts the shutter to 1/60 when shooting in appature priority but lets me go to 1/200 in manual. So what is the sync speed. I checked the manual for the camera and can't find a reference (it could be there somewhere). Does anyone know why it restricts to different speeds and whst the sync speed actually is? The flash also supports faster shutters but I dont know how to break the 1/200 barrier to test it out. Any help will be welcome. I'm slowly getting there.

[Cathus]

don't know about Nikons so can;t answer the 1/60 question.

regarding High Speed Synch, there will be a setting in your camera's menu to turn this on, there should also be a setting on the camera, you can use either.

Basically High Speed Synch allows you to use any shutter speed & fires the flash multiple times as the shutter window goes across the sensor, it's so quick you don't spot that it is several flashes rather than the one flash you normally get with under 1/200 or whatever the synch speed is.
within your synch speed range the flash fires when the shutter is fully open, with higher shutter speeds the shutter is never fully open so to light the scene seen by the sensor it needs to fire several times.

[greenwing]

You can set the Flash Shutter Speed in the menus, e1. That sets the slowest shutter speed that will be used by Aperture Priority or Program modes when you have a flash active, unless you use Slow or Rear sync, in which case the shutter speed is set for the ambient light, and the flash is basically ignored. 1/60 is the fastest Flash Shutter Speed available. In any case (in A or P) if ambient light and other settings (ISO, Aperture) demand it the shutter speed may be faster than 1/60, up to 1/200 (or beyond if Auto FP is available).

In Shutter priorty or Manual you set the shutter speed, so the Flash Shutter Speed is not important. The fastest shutter you can choose - unless you enable Auto FP Sync - is 1/200. That's the fastest shutter speed at which the front curtain is fully open, and the rear has not started to close, so the sensor is fully exposed.

Auto FP is set with menu e5. It makes the flash fire for a longer period (but still only brief) to cover the entire period that the shutter is partly open, probably about 1/200 sec for your camera. This lets the flash expose all the sensor, just like ambient light does. It comes at a cost, though. The flash power is spread over that 1/200, so the effective power drops off substantially as the shutter speed is increased. It's really meant for fill in flash where the ambient light is too bright to allow a slower shutter speed, and not to get a fast shutter speed to stop motion. The flash will stop motion better when it fires normally.

Finally, watch what mode you have on the flash. TTL-BL is best used for fill-in flash situations, where it balances the ambient and flash exposures. The standard TTL setting is better for times when you have low ambient light and want an exposure predominantly lit by the flash.

Hope this helps
Chris

[negative_optimist]

Thanks Chris and Cathus for the help. I missed the setting everytime I went through the menu as I was looking for something related to sync speed rather than Auto FP. I certainly am interested in using this for fill-in flash so this information will be put into practice.

I'm certainly not 100% on all the technicalities as still unsure what SLOW sync actually does (manual just says that the shutter speed slows automatically to capture background lighting) and I have no idea why a slowest shutter speed needs to be set for front-curtain flashes.

[greenwing]

With slow sync the camera will set the exposure for ambient light, and fire the flash at the start of the exposure, where normally the shutter speed will be set to 1/60 (or whatever you have selected for Flash Shutter Speed), which would underexpose the ambient light. Rear sync is the same, but fires the flash at the end of the exposure, making it useful for moving subjects - we usually like to see where the subject has been, rather than where it's going.

I think Flash Shutter Speed is there for flexibility. I doubt if it gets used very much. Personally, I'd like to set it to 1/125 or faster sometimes, but that's not available for some reason.

Chris

[greenwing]

Did you understand any of that?

[negative_optimist]

Hi Chris,

Sorry didn't respond before. I understand this and have got to grips with it on the camera. Need to get some practise with it though.