Since the day I reviewed the first slides produced using my Nikonos V
seven years ago I have asked myself "Why are so many of my images rubbish?" I can't blame the camera. The Nikonos V
is capable of producing magnificent images. I've concluded rather that the problem lies with my inability to use the camera to its fullest potential. The learning curve is steep. I made my greatest jump up this curve during a week of diving in on the island of Sipadan. The resort photo pro processed E6 several times a day. I was able to apply what I learned reviewing my slides within hours of exposure. Consequently my rubbish heap shrank as my relative quantity of keepers grew. When the digital SLR became an option I saw the potential right away. The prospects of 1) instant image review, 2) never running out of film and 3) autofocus, made the switch from the Nikonos alluring. I made the decision to buy a Canon 20D and a Subal C20
housing. Since my purchase I have been able to build upon my Nikonos experience while benefiting from those advantages a digital SLR affords. The principles are the same. Only the medium and the methods are different. My rubbish heap is now a virtual trashcan on my Mac's desktop.
Of course the advantages the digital medium provides are applicable to all digital cameras. I picked the Canon 20D over its competitors specifically for it's excellent low-light autofocus capability and it's low image noise. I chose the Subal housing for its high quality, ergonomics, ruggedness and it's huge optional viewfinder.
|Subal C20 Housing for Canon EOS 20D with macro port|
This article lists the basic 20D camera functions and settings and how I prefer to utilize them while shooting underwater. I'll start with basic camera operation then discuss image settings and custom functions. I'll finish with additional tips and some comments on lens choice. Note that some explanations differ depending on whether macro or wide-angle images are being shot.
Basic Underwater Operation
This switch has three settings. Make sure it is turned counter-clockwise to the third position so that the Quick Control Dial is functional.
Mode Dial: Manual
I generally shoot in manual mode for both macro and wide-angle situations. Aperture and shutter speed are then set using LCD Monitor feedback.
|Rear shot of Subal C20 housing with Canon 20d loaded|
The INFO button on the back of the 20D cycles through three LCD Monitor views. I predominantly utilize the histogram display. The histogram is a valuable tool for determining proper exposure. From studying image histograms I've developed a feel how an in-camera image will appear on the calibrated monitor on my desk at home.
Main Dial (small dial near shutter release):
While the camera is in manual mode this dial will control the shutter speed.
My two primary concerns when shooting macro are 1) Can my camera synchronize its brief (~1/30,000 sec) strobe fire so that it falls within the shutter duration? 2) Is the shutter speed fast enough to freeze my subjects motion? The best way to handle both of these concerns is to set the shutter speed to the fastest speed that is still able to sync. On the 20D this speed is 1/250 of a second. This shutter speed will reduce those areas not strobe-lit to black. I find that black usually sets off the subject nicely. If I find a suitably non-distracting, colorful background that enhances the subject I reduce the shutter speed to 1/60 sec, back off the strobes and open the aperture to allow some ambient light in.
|50mm macro shot|
When shooting strobe-lit wide-angle photos the strobe still provides the illumination for the foreground. Anything beyond 3-4 feet is primarily lit by ambient light. Since ambient light is continuous, not momentary, shutter speed becomes important. The longer the shutter is open, the brighter the background will be. I generally start with 1/125 of a second. I then evaluate the shot on the LCD/histogram. If I find the background too bright, I shorten the shutter duration to 1/180 or 1/250 sec and shoot again.
Quick Control Dial (large dial on the back of the camera)
This dial controls aperture. Since I am shooting in manual mode on a non-TTL housing the aperture is my chief means of controlling exposure. For macro shooting I usually start with F16 and strobes at half power. For wide angle I start with F8 and strobes at half power. I adjust aperture and strobe power up or down based on LCD screen feedback while trying to mind the effect changes will have on depth of field.
The Subal housing employs a conveniently placed lever for operation of the * button. I use the 20D's Custom Function 4 (see Menu Settings and Custom Functions below) to move the autofocus function from the shutter release button to this lever.
AF Point Selection Button
For precise control of focus I utilize only the more sensitive center focus point. I place the focus point on the subject and press the * button to activate autofocus. Once I remove my thumb from the * button focus is locked and I can recompose the shot if I choose.
Image Settings and Modes
Image settings and modes are accessible through the housing but I do not make many changes to them underwater. Settings and modes are dependant upon the type of shooting I am doing (macro or wide-angle). I prefer to make adjustments before I enter the water.
Each of the three buttons across the top of the camera, above the LCD panel, has two functions. One function is adjusted using the Main Dial, the other by the Quick Control Dial.
Main Dial controls the autofocus (AF) mode. I use AI Servo in conjunction with the * button for focus control (see Menu settings and Custom Functions below). This way focus will be continuous while my thumb is on the * button. If the * is not is being used for focus control, One Shot focus mode should be used. In One Shot mode autofocus will be achieved once. Refocusing will require the focus button to be activated again.
Quick Control Dial controls the white balance (WB). I shoot in RAW mode so white balance is adjusted after the RAW files are transferred onto my computer. I leave WB set to AWB (Auto).
Main Dial controls the drive mode. I use single shot mode for strobe-lit shots. The 20D is capable of capturing five frames per second in continuous shot mode. The strobes could never recycle at this pace. For ambient light shots of fast moving subjects, continuous mode might come in handy.
Quick Control Dial controls the ISO setting. Lower ISO equates to lower sensitivity to light and lower noise. Sufficient light can usually be supplied by strobes and/or ambient light. It is therefore optimal to use the minimum ISO feasible so that noise will be as low as possible. On the 20D this setting is 100. Noise performance is one place where the 20D shines. Not only does the 20D exhibit less noise at a given ISO than it's pro-sumer dSLR competitors, it offers a lower minimum ISO setting.
METERING-FLASH EXPOSURE COMPENSATION Button
Main Dial controls the metering mode. When metering the background I use Partial Metering mode. This way only the center 9% of the frame is metered. I prefer a dark background so I use the information provided by the meter to set my shutter speed one or two stops below what is suggested by the camera. The meter can't provide readings pertaining to immanent flash exposure of the foreground though. I therefore usually forego metering, and instead rely on LCD screen feedback from test shots.
Quick Control Dial controls flash exposure compensation. Flash exposure can't be controlled using this function unless the 20D is connected to a housed Canon flash. I use Sea&Sea dedicated underwater strobes so I can't comment.
Menu Settings & Custom Functions
|15mm Wide Angle Shot|
Unless otherwise listed, all menu settings are default factory settings.
Quality: RAW+Med Jpeg.
Two separate files are generated
The raw image is post processed using Photoshop. The Medium Jpeg serves as a proof for preview on my Epson P2000 portable media player. Note that if RAW or RAW+Jpeg is selected, adjustable in-camera image parameters such as saturation, contrast and sharpness will operate in default mode only.
Shoot w/o card: Off
I'd rather find out at the beginning of a dive than the end that I forgot to insert the memory card.
Color space: Adobe RGB
Adobe RGB is a wider color gamut then the default sRGB. Adobe RGB is appropriate if images are going to be processed using imaging software prior to display. sRGB is a better choice for direct monitor display or digital projection.
Review time: Hold
The last image shot will remain on screen until auto power off.
Auto power off: 2 min.
The 20D will start up instantly as soon as the shutter button is pressed halfway.
Auto rotate: On
Custom Functions (C. Fn):
C.Fn-04: 1 AE lock/AF
As discussed previously, this function moves autofocus activation from the shutter release button to the * button.
The Canon 20D employs a CMOS sensor that crops all lenses by a factor of 1.6x relative to 35mm film. As a result, a smaller image is recorded than would be on film. The captured image size is the center 62.5% of a 35 mm film image. While this may benefit macro situations by effectively making the lens longer, it is equally detrimental to wide-angle situations. A 20 mm lens on the 20D behaves like a 32 mm lens would on a 35 mm film camera. To capture the same image, the 20D user will need a wider lens than a 35 mm film shooter. Note that this formula applies only when comparing a rectilinear lens to another rectilinear lens. When comparing rectilinear to fisheye FOV (field of view) is best used.
For wide-angle shooting I use the Canon 15 mm fisheye lens. On the 20D this lens offers an FOV of 107? diagonal. In contrast, the 15 mm rectilinear lens on my Nikonos offers a slightly lower 94? diagonal FOV. The distortion commonly associated with a fisheye lens is barely noticeable underwater. There are two reasons for this: 1) most subjects found underwater are curved and 2) most fisheye distortion occurs near the outer edge of the frame and is therefore eliminated by the sensor crop.
For macro shooting I use the Sigma 50 mm EX DG Macro and the Canon 100 mm USM Macro lenses. The 50 mm lens is the more versatile of the two, allowing me to capture an image as small as 1:1, then back off and capture an image of a fish or even a diver torso. If I'm dedicating a dive to shooting macro subjects that suit a 1:1 through 1:2 magnification factor then the 100 mm lens is my favorite. Shooting 1:1 with the 50 mm lens requires that the subject be about one inch from the port. This makes lighting difficult and skittish subjects nervous. Shooting 1:1 using the 100 mm lens alleviates both of these issues by adding an additional 5 to 6 inches between the port and the subject. Both lenses can share a single flat port, with an extension added when the 100 mm is in use. I should also note that I do not feel the need for a manual focus option. My Fisheye HG20DX
Fix light provides enough illumination to allow my 20D to autofocus without a hitch. If I feel the need to tweak focus a little I remove my thumb from the * lever to lock focus then move the camera forward or back a bit.
I've found it helpful to practice using the 20D in manual mode while on land so that the control functions become second nature while underwater. It is, for example, convenient to remember while underwater which direction the Quick Control Dial must spin in order to raise the F-stop. I can always check the LCD panel but this requires removing my eye from the viewfinder. Even if I do not leave the camera in manual mode while shooting on land I've found it's helpful to maintain the image settings and custom functions listed. Although most of these settings are adjustable underwater I find it is easy to forget to change them. I'm considering creating a laminated checklist that I can review during camera setup.
As both a diver and a photographer my ability to capture a shot I can be proud of is limited by constraints imposed by the underwater environment. Monitoring my depth, air and bottom time are my primary concerns while underwater. Time behind the viewfinder is precious. When shooting the 20D I know immediately whether I successfully captured a shot of that seldom seen nudibrach. I simply shoot, review, adjust and reshoot until I have it right. Then, I move on to the next subject. My goal in switching from a Nikonos V
to a 20D was to up my ratio of keepers over rubbish. I can't say I have precisely achieved this goal. Rather I've increased the quantity of both keepers and rubbish, but this matters little when I can simply drag unwanted images into a virtual trash bin. Most importantly : I'm leaving the water knowing I've made the most of every photographic opportunity.
|15mm wide angle shot|