How to use the flash

Every time you take a flash photo, you are making two exposures simultaneously.

You are making an exposure of the ambient light, and an exposure of the flash's light.

The ambient exposure is controlled by the f/stop and the shutter speed.

The flash is controlled by the aperture.

You need to decide which one is key light and another is fill light.

Case 1 (Flash is key light)

1. Get a full ambient exposure.

2. Drop the exposure down to create a little "drama." How much, is up to you.

3. Bring your subject back up to full exposure by adding flash.

Case 2 (Flash is fill light)

Think of the sun as your main light source, and strobe as a secondary light.

Sync speed is the fastest shutter speed you can use with flash.

You cannot use a faster shutter speed than the sync speed with flash.

Sync speed is important for two big reasons:

The first and obvious reason is that fast sync helps stop motion.

The second reason, is that faster sync speeds help get enough flash power to balance with direct sunlight.

Slow sync speed

You'll want to use slow sync flash in any low-light situation when you feel that the normal flash will give you a bland, staid photo.

Another application is when photographing an action/sports subject and you want to capture the action with a panning technique (use rear curtain sync for this.)

Due to the lower shutter speeds associated with slow sync flash, you need to stabilize the camera to avoid camera shake. You’ll likely need a tripod or monopod with slow sync flash and may want to consider using a cable release to avoid as much camera shake as possible.

High speed sync HSS Vs. normal sync speed

The faster sync lets us shoot at larger apertures, which requires less flash power, which lets our flash recycle faster, which lets us shoot more frames per second.

High-speed sync flash is used when you want to use a shutter speed that is faster than your camera’s native flash sync speed, or when you want to use a wider aperture setting that requires a higher shutter speed as is often the case with outdoor daylight shooting.

High speed sync is continuous light.

Changing ISO does nothing to help since it's the ratio of ambient to flash light that's important.

Front curtain sync Vs. Rear curtain sync

In normal or front curtain sync, the speedlight fires at the beginning of the exposure.

In rear curtain sync the speedlight fires at the end of the exposure.

Flash power is flash duration time.

The Nikon SB-800 flash duration specifications are shown below :

1/1050 sec.   at M1/1 (full) output

1/1100 sec.   at M1/2 output

1/2700 sec.   at M1/4 output

1/5900 sec.   at M1/8 output

1/10900 sec. at M1/16 output

1/17800 sec. at M1/32 output

1/32300 sec. at M1/64 output

1/41600 sec. at M1/128 output