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Autofocus Underwater

Exploring the Nikon 8008 and N90 Cameras

by Ed Robinson
published 1995

Twenty years ago, when I decided I was serious about underwater photography and needed a housed SLR camera to realize my next level of achievement, my choices in camera features were much simpler than they are today. The electronic era had not hit yet, and "behind the curtain" flash, customizable programming modes, and the speed and accuracy of autofocus were not issues I had to deal with. As the years passed and technology moved on, so have my needs.

A few years ago I made the decision to upgrade my trusty Nikon F2 system to incorporate several features that I thought would improve my success rate in producing marketable images. Top on the list was to move to a camera that uses autofocus. I had two goals in mind. First was to use autofocus to help me focus faster as I scramble to capture humpback whales breach at unpredictable distances from the boat. I also felt autofocus would help me quickly focus when I was shooting with the longer macro lenses underwater. I stayed with Nikon since I had invested a small fortune in Nikkor lenses. and purchased several Nikon 8008 (801 outside the U.S.) models, and more recently a Nikon N90. I also selected Tussey underwater housings, because they seemed to make more of the camera's features available than any other type of housing. Although I am only familiar with the characteristics of these two cameras, I believe that most of my views are applicable to most SLR autofocus system on the market today.

February! Peak Humpback whale season in Hawaii, and I am ready in excited anticipation with my new autofocus 300mm 2.8 lens. Out of the corner of my eye a motion draws my total attention. A black behemoth slowly lifts from the blue sea, white water cascading in a waterfall from its massive form. Like a slow motion dream, my lens swings up and in one fluid motion I trigger the autofocus into action. Almost instantly the camera image snaps from what may have been acceptable focus and washes into a foggy blur in which I can not see the whale, the sky or the water. Shucks! (or words to that affect) what happened! Knowing that my technique needs refining, I begin to practice my aim. Almost like practicing skeet shooting, I would swing the camera up and focus on whitecaps and birds. I have learned the first lesson in autofocus photography: position the viewfinder brackets (focus target) on the subject!

In the Nikon system, autofocus is achieved when the viewfinder target is placed in an area of the image where there is some visual contrast. Most patterns will work, but more important, what will not work is uniformity. A white billowing cloud usually has enough gray shadows mixed in with white for the autofocus to work. However, the blue, cloudless sky behind the humpback whale left my camera without any reference lines or patterns to bring into focus, and the camera began to "hunt" for focus. If I had been more accurate in placing the breaching whale in the center of the viewfinder, the camera would have had little trouble focusing faster than I could achieve manually. With a bit of practice aiming the lens, and learning to wait until the focus target is on the subject before activating autofocus, I was able to put autofocus to its true calling.

So, now I'm the best aim in the west with my 300mm lens. Out of the corner of my eye a motion draws my total attention. A black behemoth slowly lifts from the blue sea, white water cascading in a waterfall from its massive form. With assured confidence I swing my camera to my eye and view a whale so far out of the water I can see air between it and the ocean surface! Excitedly I trigger the shutter ... and wait ... and wait. Finally the motor drive takes over and I wrap off three or four frames. But the magic moment has been missed. All I can capture is an image of the whale already surrounded by a white wave as it returns to the sea! The frustration I feel, at missing that exceptional image of an airborne whale, is my second lesson on autofocus.

The 8008 and N9 cameras permit two autofocus techniques: Single Servo, and Continuous Servo. In English, Single Servo means the camera will not release the shutter until it has confirmed that the lens is at optimum focus. Selecting Single Servo will make the camera almost idiot proof, since it will not take the picture if it is out of focus. However, I missed the breaching whale image because of a combination of motion and spray that confused the autofocus system. Single Servo refused to take the picture until the subject was clear and sharp. Continuous Servo, on the other hand, would allow the shutter to trigger any time the shutter release is pressed. The intended use of Continuous Servo is to track the focus of a moving subject, such as a runner, coming toward the camera. Had I selected Continuous Servo, the picture would have been taken, even though the camera did not see the whale in focus. Lesson number two, I must choose the correct focus technique!

There are several conditions in which I generally override autofocus. Due to the minimal depth-of-field available in macro photography I must be very selective in which part of the subject I select prime focus (usually the eye) as I compose a picture. When the subject is stationary, or it's movement is predictable, Single Servo has a feature which works best. Once Single Servo locates sharp focus it locks and holds that focus for as long as the shutter button is slightly activated. With this feature it is quite simple to focus on the eye of a fish, and then realign the image to achieve the desired composition. Extreme macro images, however, are not this simple.

The conditions that thwart autofocus are low light, lack of contrast, and excessive motion in the camera or subject. Extreme macro photography can introduce all these elements at one time. It seems like the most beautiful nudibranchs are usually ½ inch long, hiding under a ledge, and in the surge. And my mind sees an award winning image, at 1:1 reproduction. With autofocus and a 105mm macro this is one of the most difficult shots to pull off, but it can be done.

The problem with autofocus is that it needs to see the lines or patterns in the subject, and it needs to be close enough to the correct focus to even see the subject. Otherwise, all the lens can do is "hunt" by focusing from infinity to minimum focus and back. A strong aiming light mounted on the camera housing is beneficial to focusing on this nudibranch. When the subject is brightly lit, the camera can easily distinguish the lines and patters (if they exist) on the subject and quickly locate focus. Ocean surge creates an additional challenge at 1:1 (minimum focus) because the depth-of-field is less than ¼ inch and finding and holding focus can be extremely difficult. This is a situation where manual focus would be helpful, but my story is about autofocus so I'll let you peek into my bag of tricks.

The nudibranch scenario above can be successfully achieved when I use Continuous Servo to "trick" the camera into taking the picture NOW! The first step is to get the camera to focus at 1:1, minimum focus. I usually do this by focusing on my finger! Why? Because... It is easy to hold my hand steady, close to the camera, in surge. Then I slowly move the camera close to the subject, until I can see it in focus. Since the surge wants to move me back and forth, I do not attempt to stay still. Instead, I begin moving the camera back and forth, in and out of focus. Once I am in a predictable pattern I trigger the shutter (set on Continuous Servo) as the subject approaches sharp focus. The bright aiming light helps me see the image, which is important since I am no longer relying on autofocus. This technique is the same as I would use with a manual focus lens, and produces as many usable images as I would normally get from a manual focus camera.

If you are considering buying an autofocus camera for underwater you are probably waiting for the crowning point that will support your decision to move ahead or stay with manual focus. Okay, here are my thoughts. The main advantage of autofocus is the ability to focus quickly, and accurately. Those of us who don't like to wear glasses but need to, may find the accuracy of autofocus reason enough to go this route. I have also found that the Nikon cameras can focus accurately in light so dim I would have a problem focusing manually! My original need - to quickly focus a telephoto, or macro lens - works in my favor most of the time. However, I feel it is critical to get an underwater housing that allows the photographer to override autofocus. I also feel autofocus should be limited to normal and telephoto lenses (35mm and up.) Wide angle lenses do not have the critical focus problems of longer lenses, and it is common to place the main subject in wide angle pictures off center, which will throw the subject focus off. In a word - "yes" go for autofocus, with the understanding that there will be a learning phase, as you get used to new techniques.

-- Ed Robinson