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The Basics

The Nikon Coolpix 990, 995, and 5000 all have the ability to use external flash. We'll start with the simplest method. To use external flash you would normally need:

• For the 990 and 995: the AS-E900 cable, a Nikon-compatible flash, and something to hold the flash (such as the SK-E900 Multi-Flash Bracket).
• For the 5000: a Nikon-compatible flash with a standard hot shoe foot.

The first issue you'll face is what is a "Nikon-compatible flash?" The answer depends a bit upon what you want the flash to do. If you want the flash output to be controlled by the Coolpix, you need a flash that is capable of Nikon TTL modes. All currently available Nikon Speedlights fit this bill, as do a few third-party flashes, such as the well-regarded Metz line.

If you don't care if the Coolpix controls the flash, virtually any flash capable of Automatic flash mode should work (but you should turn off the internal flash when using these units). While the Nikon manual warns of possible damage using third-party flash units, this warning is a bit outdated, as virtually all flashes currently manufactured adhere to a low-voltage standard (years ago, many flashes placed high voltages on the contact pins, which could damage the low-voltage electronics of modern equipment).

Modes

Nikon's manuals have a tendency to describe a mishmash of "modes." Some things they call modes are really just option settings. Here's a quick overview:

• TTL flash mode. Stands for "through the lens," though this is NOT how flash measurement is done on the Coolpix models! When you set a Coolpix to TTL mode, that means that the camera controls the amount of flash by watching the flash reflection with a camera-mounted light sensor and shutting off the flash when the camera calculates that enough light has reached the subject. The built-in flashes always use TTL--it cannot be canceled. If your external flash is Nikon TTL-compatible, the camera can control it directly, and you generally don't have to fiddle with any extra settings.
• Automatic flash mode. In Automatic flash mode the amount of flash is calculated and controlled by the flash (it, too, has a light sensor). Thus, in automatic flash mode, the only thing the flash really needs communicated from the camera is when to start the flash. If your external flash is Automatic mode only, you usually have to set ISO values on the flash and to match aperture values on both the flash and the camera. This extra work can slow you down and keep you from shooting quickly in candid situations.
• Auto flash. Not to be confused with Automatic flash mode! If the Coolpix displays Auto along with the flash symbol, that means that the camera will determine situations when it thinks flash is necessary and use it. You have no control over when the flash is and isn't used.
• Anytime flash. If the Coolpix displays only the flash symbol (no Auto), the camera will fire the flash for every shot.
• Slow sync. This isn't really a mode, but the removal of a camera-imposed limit. In Program and Aperture-preferred exposure modes, Nikon cameras usually impose a lower limit on shutter speeds. Setting slow sync on your Coolpix removes that limit.
• Red-eye Reduction. Again, not really so much a mode as an option. With red-eye reduction, the flash is fired prior to picture being taken (attempting to make the subject's pupils smaller), then again during the picture. Red-eye reduction only works with internal flash units. I generally advise against using this function, as it introduces additional shutter lag, annoys the subject, and still doesn't remove the red-eye!

Which Flash Should I Buy?
If all you'll ever use the flash with is your Coolpix, fancy features such as flashtube zoom, repeating flash, rear sync, red-eye reduction and autofocus assist, and so on, can't be invoked from the Coolpix so are features you're paying for that you can't use. In general, a simple flash capable of TTL and/or Automatic mode is about all you need. Nikon has just introduced just such a flash, the SB-30, and of the current Nikon offerings, it probably is the most suitable if all you'll ever use it on is a Coolpix. The other flash in the Nikon lineup that makes sense with a Coolpix is the SB-50DX, mainly due to its ability to be used wirelessly.

Wireless
Most Coolpix models can trigger external flash units wirelessly (the SB-50DX or SB-80DX being the models of choice, with their built-in wireless controllers). That's because flash units emit a significant pulse of infrared light, which wireless remote sensors can detect, even in bright situations. One common method of triggering a remote SB-50DX is to put a filter over the internal flash that blocks all but the infrared spectrum (a piece of processed unexposed film works pretty well as a filter). Make sure NOT to block the TTL sensor on the Coolpix, however, as it is still controlling the overall exposure if the remote flash is set to TTL (or Auto Wireless in the case of the SB-50DX). Already have a flash but want to make it wireless? Nikon sells the SU-4 accessory, which has the sensor and a hot shoe to mount your flash on.

Gotchas

• 995 Flash must be popped up. Even if you have turned off the internal flash, the Coolpix 995's flash must be popped up, as the TTL sensor is next to the flashtube.
•  Watch the zoom position. Most Nikon and third-party flash units allow you to "zoom" the flashtube to specific 35mm lens coverages. With a Coolpix you should probably manually zoom the flashtube to the 28mm position or wider.
• Check the TTL sensor. First, it should be unblocked. Second, the external flash shouldn't be pointed in a way that stray light from it can directly enter the sensor.
• For Automatic flash mode, you need the camera to be in aperture-preferred exposure mode. Because apertures aren't communicated directly to the external flash, you'll need to be able to set a specific aperture on the Coolpix.
• Watch how close you get. All Nikon Speedlights have minimum limits in the amount of flash they can produce. If you're trying to use a Speedlight to light macro photography shots, you're likely to find that you need to move the flash 2' or more away from the subject in order to avoid overexposed photos. The more powerful the flash, the greater that distance is likely to be.
• Preflash messes up wireless flash. The Coolpix 775, 880, and 885 fire a pre-flash prior to the actual exposure, which is used to help calculate the exact balance of flash and existing light exposures. Unfortunately, these preflashes are seen by wireless remote flash units, and the remote flash typically fires before the shot! Coolpix 99x models don't have this problem, however.

Eureka Lee [is84007@cis.nctu.edu.tw] asks: In the Coolpix 995 manual, p.70, "Check points" reads: "The Flash output of other Speedlights connected to the sync terminal is synchronized with the built-in Speedlight." When in slow sync mode, will external flash (say, PZ-5000) sync accordingly? Slow sync seems to be Nikon's name for "rear sync," which you said Coolpix won't support.

Thom's Response: First, slow sync is only the removal of the lower limit of shutter speeds on the camera body (Nikon bodies usually limit shutter speeds to 1/60 second with flash). Rear sync does the same, but also moves the point at which the flash is fired during an exposure to the last possible moment. For slow sync, only the body has to support it. For rear sync, both the body and the flash have to support it. Thus, the answer to your question is yes, you can use slow sync with your camera/flash combo.