Using Flash and longer shutter speeds at dusk

Hi gang,
I'm shooting a wedding for a friend this weekend (nothing like waiting until the last minute to ask a question) and the ceremony is right after dusk outdoors. There are going to be fires burning in the background so there will be a lot interesting light to capture in the background. I wanted to shoot with flash but leave the shutter open for a bit to capture some ambient light. I like that effect of the initial flash plus the blurry ambient light motion (know what I mean?). I just don't want that flat flash look. I'm using a Nikon SB-800 flash on auto (not TTL) with my Nikon F3 with Fuji NPS160 (open to other film choices). My knowledge of the SB-800 is very minimal since I'm borrowing it. How can I figure out how much compensation to give with the longer shutter speeds? I am going to go out to the location when the weather clears up and run a test roll at the exact time the ceremony will be. Any suggestions before I start testing? I'm thinking shutter speeds around 1/8 to get some blur. I have a Sekonic L-328 flash meter that I'll use be using for the tests.

Obviously, this isn't your usual wedding photography because they aren't your usual couple.

Thanks in advance for your suggestions,
Ara

Dude, I don't know but I eagerly wait for the answer.... Wouldn't 1/8, even at dusk still make your main subject (that you are flashing) kind of blurry too?

I've experiemented with metering the background with 1/30, setting the camera on manual to 1/30 at, say, F4 and flashed the main subject with my vivitar 2 stops lower... The jury is still out on the results but it looked a lot better than my past, full flash crap...

I think you need to use the sync speed of 1/60 for the F3, if you use any other shutter speed the shutter will not be wide open when the flash fires. A camera with a leaf shutter will syn at any speed with differnt guide number. A newer camera like the F4 or 5 has a higher flash sync not lower. Some older camera have a sync at 1/30. Or is the F3 a 1/30? Double exposure? Good luck.

Flashing with ambient light.

What your up to is called dragging the shutter. Once you have the main flash worked out, you drag the shutter with a longer shutter speed for the background exposure. This is a pretty basic studio thing to do, depending. It's also possible to second curtain the flash synch with subjects in very dark conditions. A low ISO film would be prudent here as it will build foreground exposure slowly causing less subject movement exposure. Most standard photo books cover this.

To understand what you want to do, figure a reflected meter reading will give you a zone 5 exposure for the background. If your aperture is set at say F8 and at 15ft for the flash exposure according to a guide number, you'll find the amount of difference between foreground and background in the shutter speed settings when using a manual flash; Think studio flash here as it's easier to understand. A ttl flash model will just increase the flash output compared to a nuts and bolts, this is what your getting out of me manual flash. Hypothetically, if the flash synch for this picture is 1/60 at F8 according to your meter for the group exposure and the medium zone 5 back ground exposure is 1/15 at F8 , your going to be 2 stops down in exposure on the background at 1/60th. So where does that put you with your film latitude and what your trying to record? Probably pretty good if you have brightspots in the sky. Sometimes as I mentioned above what you want to do is second curtain the flash, expose for the background placing it where you need it and then flashing the main subjects in TTL. The best way to figure it all out is to test. Since it's a wedding, a half black, and half detailed white test board would be great to use. If you can stick it in the ground use a 5ft tall stake and a peice of painted cardboard. Try using NPZ. For all accounts most rate it at a 1/3 to a 1/2 stop down in speed. Say ISO 640 or even 520, and it will boost contrast a little too.

I have not done much studio work, will this work with a focal plan shutter? I always thought that flash will not sync with any other shutter speed other than the sync speed as the curtain will not be wide open. I have not used an F4 or N90, so I don't know if newer cameras will sync at lower speeds. Or is this a double exposure tech?

The sync speed is the fastest speed that will work. Slower will work just fine. Some cameras might make it difficult to set the speed with the programming wanting to use the sync speed. If the camera can be set manually that won't be an issue.

Wish I had sme more exact data - but I can tell you this much: I have done some night shooting with 400 film using this method - and I am still alittle hit and miss but the ones that did come out, were wonderful. For night time I set shutter at 1 or 2 seconds, apperture at 16 or 22 (I did have some street lights, etc) and then flashed my Sunpak manually from where I wanted the light to come from - as soon as I heard the shutter open or saw the flashing light go off on the timer. I understand you will have to adjust a bit - I found my ability with light meters and the ability of the meters available to me rendered the instruments useless, so I arrived at these values by trial and error. Got some wonderrful results and had some flexibility with the flash since I could run around with it in hand - you may have to have an actual mechanical/electric synch since I doubt anything over 1/4 sec would be applicable.

Though I used TTL on my F90X here is what I did.
Match shutter (M) and F-stop to underexpose background -1 to -2, mostly the latter (TTL matrix) giving a shutterspeed around 1/8 sec, so the flash will give light to an
N-exposure of the main subject. Normally this will freeze movements within the flash range but not in the background, I like the effect and have seen only a few blurred pics. I use it alot when photographing family gatherings.
Søren

My Maxxum 7 does this automatically, and it normally goes from a shutter speed of 1/60 down to 1/10 or so, using ISO100 film with the built in flash. So, it takes 4/5 stops from the original values, but I also know that the flash doesn't have fixed burst, so I don´t know if it compensates there as well. Don't know if it helps.