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Underwater Photography Part 2

Text And Photographs by Paul Janosi

Techniques Of The Nikonos System

[picture of underwater 
	camera]
 

II USING ELECTRONIC FLASH UNDERWATER

  1. Underwater Photography Part 1
  2. TTL FLASH
  3. TTL Flash Settings
  4. Full Power Flash Signal
  5. Fill in Flash Exposure
  6. Flash Placement and Direction
  7. Manual Flash Exposure
  8. Shutter Speed
  9. Multiple Flash
  10. How to Use Two Manual Strobes
  11. How to Use Two TTL Strobes
  12. Slave
  13. Power Source
  14. Underwater Photography Part 3
  15. Underwater Photography Part 4
  16. Underwater Photography Part 5

When light enters water a number of changes occur. The intensity is reduced, the quality is altered and it is refracted. On the surface the visible light is made up of all the colours of the rainbow, but under water the different wavelengths of colour penetrate to different depths. Red for example is absorbed in shallow water and blue penetrates the deepest. Because of the differential absorbance of light at depths greater than 25 feet most available light, most available light photographs are rather monochromatic. At 15 feet red is not distinguishable in available light, at 30 feet orange disappears and below 60 feet yellow is invisible. To show the true colour of subjects supplementary light is needed as either fill or keylighting. The use of artificial light underwater adds colour contrast to the image, depending on light source and distance may increase depth of field, and having control over the placement and direction of the light lets you create images that were not possible with the existing available light.

TTL Flash

The Nikonos SB 102 and SB 103 underwater flash units designed by Nikon for use with Nikonos V camera provide automatic through the lent (TTL) flash control. In over simplified terms, after the flash is fired, a light sensor inside the camera measures the light coming through the lens and turns the flash off when the proper exposure has been reached.
Since the camera automatically controls the flash output from the SB 102 or SB 103 strobes, this frees divers from complicated calculations allowing more time for composition and creativity.

TTL Flash Settings

  1. Load the desired film in the camera and set film speed dial. For beginners ISO 100 is recommended.
  2. Set shutter speed dial for AA@ auto.
  3. Set Nikonos SB 103 to TTL; the Nikonos SB 102 must be set to TTL with the shooting mode selector and the power switch must be turned on. For subjects 3 to 4 feet away set aperture to F8, set focus, compose and start taking pictures.

    Full Power Flash Signal

    Both the SB 102 and SB 103 have a full power flash signal. If the ready light blinks just after you have fired the flash, the flash has fired at full power. This indicates that the automatic range may have been exceeded and the pictures may be underexposed. Either open up the lens 1f stop or move in closer to take the next picture.

    Fill in Flash Exposure

    Balancing available and artificial light is quite simple with the Nikonos V. When the SB 102 or SB 103 flash is connected to the camera on automatic or on manual setting faster than 1/90 sec, the shutter speed is automatically locked at 1/90 sec. However, the shutter speed that would match the aperture setting if you were not using the flash will still blink inside the camera viewfinder. Simply aim the camera at the desired background and select the appropriate f stop setting which will cause the 1/1125 and 1/60 second LED to blink. Recompose the desired image and shoot. The flash provides the same level of illumination falling on the foreground subject as the available light illuminating the surroundings or background. The image created will have a great depth of field. The foreground subject is brightened by the flash creating a colour contrast and the background is illuminated by the sun.

    Flash Placement and Direction

    Even illumination of the subject occurs when the flash is aimed squarely at the subject and the beam angle of the unit equals or exceeds the angle of the lens used. For the Nikonos 35 mm and 28 mm lenses flash coverage is generally not a problem. However, with the Nikonos 20 mm lens which has a 78 degree coverage and the 15 mm lens which has a 94 degree coverage, the accessory diffusers supplied with the SB 102 and SB 103 strobes must be used. There are two ways to position and aim the flash. One is to attach the flash directly to the camera, the other is to hand hold and aim the flash unit.

    When using the Nikonos arm and bracket assemble the equipment according to the procedure outlined in the instructions. This will ensure that the flashes axis will always intersect with the lenses optical axis even if the flash head is moved up or down the arm.

    Hand holding the flash requires more skill but gives you a great deal of flexibility in positioning the flash. The drawbacks to hand holding the unit are that there is a potential for inconsistent result because of poor flash placement.

    The flash should be positioned high and to one side of the camera. This position most closely approximates the light coming from the sun, providing even and natural looking illumination. It also helps to reduce back scatter because any particles illuminated by the flash are reflected back toward the flash instead of the lens.

    Aiming the flash is also complicated by refraction which happens where ever there is an air/water interface such as at your face mask or camera lens. Because of refraction, objects appear approximately 25% closer and larger than they actually are. So when you aim the flash you have to aim it a the actual not the apparent position of the subject. For example, if the subject appears to be at 3 feet, aim the flash slightly behind to 4 feet.

    The built in modeling light in the Nikonos SB 102 takes care of this problem, since you can see exactly where your flash hits the subject. Attaching a small modeling light to the SB 103 serves the same purpose and is especially helpful on night dives.

    Manual Flash Exposure

    Manual flash exposure is based on a dial on the back of the Nikonos SB 102 or a stick on decal on the Nikonos SB 103. Moveable calculations or decal are sometimes hard to read under water because they contain too much information. For simplicity many photographers create their own table of f stops an flash to subject distances. These can be marked on a piece of tape or written directly on the side of the flash. Both the Nikonos SB 102 and SB 103 flashes have the ability to change power from full, 1/4 to 1/16 power when they are in the manual mode. The advantage to such control is the conservation of battery power and the reduction in recycling time. You can also bracket exposure using the variable power control.

    I use the following tables of manual exposures with the Nikonos SB 102 and SB 103 strobes. They are based on apparent distances.

    Manual Exposure Table Nikonos SB 102
    ISO = 50 or 64
    Apparent Distance Full Power 1/4 Power 1/16Power
    1 Foot f 22 (16.0) f 11 (8) f 5.6 (4)
    2 Feet f 11 (8.0) f 5.6 (4) f 2.8 (2)
    3 Feet f 8 (5.6) f 4.0 (2.8) f 2.0 (-)
    4 Feet f 5.6 (4-5.6) f 2.8 92.0 -
    5 Feet f 4-5.6 (4) f 2-2.8 (-) -
    6 feet f 4 (2.8) f 2.0 (-) -
    Use the f stops shown in brackets when using optional wide angle diffuser.
    Manual Exposure Table Nikonos SB 103
    ISO = 50 or 64
    Apparent Distance Full Power 1/4 Power 1/16Power
    1 Foot f 22 (16.0) f 11 (8) f 5.6 (4)
    2 Feet f 11 (8.0) f 5.6 (4) f 2.8 (2)
    3 Feet f 8 (5.6) f 4.0 (2.8) f 2.0 (-)
    4 Feet f 4-5.6(4.0) f 2.8 (2.0) -
    5 Feet f 4-5.6 (4) f 2-2.8 (-) -
    6 feet f 4 (2.8) f 2.0 (-) -

    Shutter Speed

    The cameras focal plane shutter can be synchronized with flash at 1/30, 1/60 or 1/90 sec.

    On deep dives many wide angle photographers choose 1/30 sec as their shutter speed so that the camera can record the detail in the non strobe lit areas of the photograph.

    Depending on flash to subject distance the flash power may also have to be reduced in order not to overexpose the foreground.

    Multiple Flash

    Two flashes may be connected to the Nikonos V with a double TTL sync cord. The Nikonos double bracket attaches to the baseplate of the camera. Twin TTL strobes can be attached to the left and right sides of the double bracket with the strobe arms. The strobes are usually placed high and aimed 45 degree.

    Two strobes provide illumination over a wide area; the increased intensity of light provides increased depth of field and two strobes allow you to control the contrast between the shadow and the highlight areas.

    How to Use Two Manual Strobes

    When two equally powerful flashes are both illuminating the same subject area, set the aperture one f stop smaller than you would when using only one flash. For example, if using one SB 103 strobe the exposure at 3 feet is f 8. Aiming two SB 103 strobes on the same area the exposure is f 11.

    When two equally powerful flashes are lighting different parts of the image such that there is little or no overlap of illumination the aperture is set based on the power output of a single strobe.

    When two strobes are illuminating the same subject area and one strobe is stronger than the other ( such as when using Nikonos SB 102 and 103 together or when one flash is used with a wide angle diffuser and the other is not ) the exposure is based on the power of the two strobes combined. For example, at 3 feet SB power output is f 8, SB 102 is f 11. Therefore set aperture to f 11-16.

    If two strobes with different power output are illuminating different parts of the image the exposure is based on the power output of the strongest strobe. The weaker strobe will provide fill lighting on the shadow side of the image.

    How to Use Two TTL Strobes

    No exposure compensation is required when using two TTL strobes connected by the dual sync cord. When the two equally powerful flashes overlap, twice as much light falls on the subject. This extra light can be used to extend the automatic range of the flash or the depth of field can be increased by selecting a higher f stop.

    When two flashes of different intensities are used on TTL the exposure should be based on the automatic range of the more powerful flash. The weaker TTL flash will provide the fill light only.

    Slave

    Another useful feature of the SB 102 flash is that it can be used as a slave to an other flash. The flash has a light sensor internally connected to the flash firing mechanism. When the sensor picks up the blast of light from the flash triggered by the camera, it fires the slaved flash a split second later.

    During slave flash photography avoid other photographers taking flash pictures because the burst of light from their flash unit will trigger your slave. For multiple slaved flash operation all flash units must be in the manual shooting mode.

    Power Source

    The use of Nicad batteries is recommended with both flash units because of their short recycling time.

    The Nikonos SB 102 requires 6 C type batteries. Nicads will provide a minimum of 70 flashes with an approximate 5 sec recycling time.

    With Alkaline-manganese batteries the number of flashes increases to 120 but recycling time increases to 14 sec.

    The Nikonos SB 103 requires 4AA batteries. Nicads provide a minimum of 50 flashes with an approximate 6 sec recycling time. Alkaline-manganese batteries provide a minimum of 130 flashes but the recycling time increases to 9 sec.

    For best performance, change and use Nicad cells in labeled sets. Do not mix old and new batteries or Nicads that have been charged for different time.