Underwater Strobe Buyers Guide (revisions coming soon)
By James Forte Copyright 2007, Do not reproduce with out the permission of James forte

Guide numbers, Color temperatures and Beam angles. What do all these terms mean? These terms are the way strobe specifications are defined by the manufacturers. These specs help photographers decide which strobes will best suit their needs. Specifications supplied by the manufacturers have been put together with brief definitions for your use in purchasing a new strobe. With the information compiled in this guide and some guidance from the right users ie. Pros, U/W photo retailers, friends, club members, etc. you can feel confident in making the right decision on your next strobe purchase.

First a quick lesson in why we need strobe lights underwater. In shallow water less than 15 feet we can use ambient or available light to get results when photographing some subjects. Without strobes most photos will be monochromatic lacking the rich, brilliant colors we see in our favorite magazines and books. To get rich saturated colors photographers have coupled strobes with their camera to do what's called "Painting with light". With the right strobes and techniques you to will get colorful images to place on your wall or submit for the next magazine cover.

The following definitions are brief for your understanding of strobe terms. To get more detailed information be sure to email James for more specific definitions.

Strobe manufacturer and model Definition
It is what it is. Today's strobe market is filled with many different brand names and models. It's always best to do a little research on makes and models to find out reliability and performance from those who have used the strobes.

Guide Number
This is the way most manufacturers define a strobes power output. A guide number is determined by multiplying the aperture times the distance. This will give you a strobe to subject distance for exposure. If your given a guide number you can plug it into the formula GN= Apt x distance to figure out a strobes capabilities. It's best to test strobes for their accuracy using a flash meter on land to measure their guide number as they may very. Generally the higher the underwater guide number the better. Note that land guide numbers are almost double underwater guide numbers.

Power source
The type of battery and quantity used to power a strobe. Most strobes accept alkaline batteries or nicad pacs. Some strobes now except lithium batteries which last twice as long as alkaline. Rechargeable batteries can also be used for those who use several strobes or are worried about weight allowances when traveling.

Number of Flashes
With fresh batteries the number of full power flashes a strobe will fire. This will change depending on battery type and age of battery. Think of this number as the quantity of rolls of film you can shoot per fresh battery set. Four to five rolls of film is considered good for a fresh set of batteries by most.

Recycle Time
The period of time till the flash is ready to fire again after flashing. A good strobe can recycle in under five seconds after a full power dump. Most recycle times range from 2 to 10 seconds, the faster being best.

Color Temperature
A rating in degrees Kelvin given to flashes in comparison to normal day light which is about 5500* Kelvin. Most films used for photography are balanced for day light at 5500* Kelvin. The ideal strobe will fire a full power blast at as close to 5500*K as possible. Strobes with higher color temps will give off hot hues with less warmth. Its best to use a diffuser on hot strobes to tone down their temp. and create more warmth. Different temperatures will change the hue and saturation of colors and should be taken note of.

Firing modes
Settings on a strobe defined as follows. Manual mode will dump what ever power setting the strobe is at when the cameras trigger is depressed. TTL firing is the camera judging and exposure by the amount of light reaching the film plane after the strobe is fired. When enough light is sensed for proper exposure the strobe turns off automatically. Slavestrobes react to other strobes firing and the output is determined by the power setting of the slave. Test mode for checking recycle time of batteries and if the strobe is firing.

Power Settings
The intensity of the strobes power compared to the strobes capable output, GN. Power settings vary depending on the make and model. The various settings allow you to control the amount of light emitted by the strobe when shooting manually.

Beam Angle
The area of light coverage by a strobe. The wider the angle of coverage a lens has the wider the angle your strobe needs to be. In macro you don't need as wide a beam as you might in wide angle photography. If one strobe is what you plan on starting with you can use a strobe with a higher beam angle for wide angle and macro, but not the inverse.

Diffuser
Used to spread out the beam of a strobe and reduce color temperature. When used overall power output (GN) is reduced. Diffusers can be made also to create special effects.

Ready Signal
Let's you know when the strobe is ready to fire again. Note some strobes are not completely at full power when the ready light comes on and you should wait a bit longer. You can test for this characteristic using a flash meter.

Modeling Light
A built in spot light that shows which direction the strobe is pointed. Auto focus SLR's focusing improves with the use of modeling lights. Excellent feature for night diving photography.

Strobe Housings
Designed to house land strobes for use underwater. Land strobes have various features if accessible that work well with housed SLR's. Also they can be used topside with the same SLR's. Most Land strobes are typically not that powerful and don't have coverage for lens wider than 28mm.

Few last words on selecting strobes
Look into your crystal ball and try to pick a strobe that will grow with your needs. As your lens arsenal grows and your photography improves you'll probably want two strobes. Did you choose a strobe make that will be easily coupled with other strobes. Are the batteries compatible between strobes and even better your camera too. Does the strobe your looking at compatible with your camera. With so many different makes and models of both camera's and strobes be sure to contact the manufacturer or an authorized dealer for concerns you may have. You should always consult a specialized underwater photography retailer for current costs and trends. Most I think would agree it's best to consult with more than one source to back up claims you may read or hear.

I prefer Ikelite and Sea and Sea strobes .