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Why Digital?

by Chris Hacking

    The easiest and most practical way to learn underwater photography is with a digital camera. Aside from inherent advantages of digitals (like no developing and easy storing, copying, and sharing of photos), a digital camera also makes underwater photography much easier. A reasonably large memory card can allow many times as many pictures on a single dive as the largest rolls of film, and getting rid of the bad shots doesn't cost anything. Digital cameras also record such vital information as shutter speed, aperture, flash mode, ISO, white balance, focal length (zoom), and many other data useful when analyzing pictures. Finally, most digital cameras also have the abilities to take short digital videos. Of course, a dedicated video camera takes better ones, but there is a lot to be said for a nice, large still photo. However, some things just look really great in motion, and only a digital camera can do both. There are some concerns though... digital cameras can produce lower-quality pictures, if you let them. Some digital cameras also have a noticeable shutter delay, which can make good composition tricky.

Take many pictures, then delete
    One of the most significant advantages of a digital camera is the ability to take a over a hundred pictures (three times a large roll of film), deleting 30 as soon as they're taken and 30 more when viewed later on a bigger screen, and still come up with more shots than are possible with film (changing film underwater is... impractical). In fact, a large card will often have enough space for two full dives, so as long as the batteries are full it is reasonable to seal the camera in its case before getting on a boat in the morning, dive all day, and not need to open the case until back on dry land. In particular, the ability to see the most recent shot makes it easy to decide if another photo needs to be taken of the last target. For example, I may occasionally cut off the nose of a fish, or have a some fish swim right in front of my target just as the picture is taken. With film, those are not only wasted shots, the photographer might not even realize that the picture needs to be retaken until the film is developed days (or weeks) later!

Memory cards and high resolution
    People seem to be completely megapixel-crazy, sometimes. I will not deny that high resolution is nice, but it doesn't actually guarantee better photos. For sharpness and clarity, the things to watch for are the size of the light-detection chip, or Charge-Coupled Device (CCD), and a good lens. However, it is generally true that, when possible, the largest possible resolution should be used. One downside of this is that it uses up a lot of disk space; we have many gigabytes of digital photos, with each shot usually taking up 1.5-2 megabytes.
    Large photos will fill up a memory card quickly. Since changing cards and film are equally impossible underwater, (in fact, the case should be rinsed and then completely dried on the surface before opening) it is important that there be enough space on the card for the shots you want to take. I suggest that you make sure that your card has space for at least 80 shots, or maybe 130 for two dives, with time to clear bad ones in between. I might only end up with 20 or 30 good pictures after a dive, but I usually throw away (after analyzing) at least that many less-than-excellent shots. These numbers are, of course, much higher than are possible with a film camera.

File types and compression quality
    Of course, the storage needed depends largely on the compression used. JPEG is the most common format by far, but the JPEG algorithm reduces quality every time it is used. For underwater shots (indeed, for all digital photography), I recommend using the highest-quality compression available (if you use compression at all). This does result in larger files, but the smaller ones are barely worth taking sometimes. One thing about JPEG compression is it tends to reduce the color depth significantly, especially in the blues, since normally the eye does not discern changes in blue as much. This can lead to the whole underwater background appearing very uniform, with only a few graduations as distance or depth increases. Comparing my JPEGs with professionally-shot film pictures, this is one of the greatest differences I note.
    To avoid compression loss, some cameras allow pictures to be stored in RAW (or TIFF) formats. RAW files contain all the data, unchanged, as it came from the CCD. In effect, they are as perfect as the camera can produce. Furthermore, with decent editing software, these pictures can be brightened, contrasted, color balanced, saturated, or a number of other things without introducing the 'graininess' that such manipulations often cause to rendered digital photos. RAW files usually require proprietary software to read, however; they are specific to the chip that produces them. TIFF files are not camera-specific; most image software can display them. However, like RAW files, they are many times larger than high-quality JPEGs, greatly reducing the number of shots that can be taken on a single dive. With the correct software, either, can be converted to JPEG (.jpg) or many other formats easily, for storage or for posting on the web. All the pictures on this site are GIF or JPEG, which are viewable on all computers.

Good lenses make good cameras
    It should be mentioned that one of the greatest single features of a good camera is a good lens. Although this issue is not really relevant to the film-vs.-digital debate, as either kind of camera can come with a great or a terrible lens, it is important when considering a camera to buy. A good lens will allow better shooting in a wider range of light levels, better optical zoom (telephoto) capabilities, and more options for apertures (tight apertures are useful because of a greater depth of field). For example, my lens cannot use a wide aperture like f2.8 while zoomed in, and the tightest aperture it is capable of is f8.0. However, while I'd like to get a better lens, this one works fine (and the lens isn't removable on my camera anyhow).  Note that the Martian Rover uses only a 1 mega-pixel CCD (and a superb lens).

EXIF data tells you (almost) everything you need to know
    One GREAT advantage of digital cameras for anybody learning (any kind of) photography is that the pictures contain data about themselves and the state in which they were taken. EXIF (EXchangeable Image File format) information almost always contains a large number of useful statistics that your camera stores in the picture as it's taken (note that EXIF data is not normally viewable as you look at a picture; it is stored more like the Album/Artist/Composer/Genre/etc. data on an MP3. Check your picture viewing program to see if it will let you read EXIF data.)
    EXIF data can be very useful while analyzing what went wrong (or right) in any shot. For example, if some shots are blurred and others aren't, you can compare their shutter speeds and from those, learn what the usable range is. Similar comparisons can be made with focus, brightness, graininess, color balance, flash settings, compression quality, even one camera vs. another (I have copies of photos from a friend whom I dove with several times, and can sometimes compare his shots with mine of the same subject). Since this data is stored with each photo individually, it is very easy to take a group of similar photos using different options and compare exactly what is different in this shot (try examining two pictures taken at different ISO settings, and the graininess of the higher ISO may be startlingly obvious). EXIF data is stored automatically by all digital cameras that I know of.

Easily adjust ISO
    For those familiar with film cameras, the casualness with which I mention taking pictures at different ISO values may be surprising (generally, a roll of film is all shot with the same ISO). However, most digital cameras can switch their CCD's light sensitivity (ISO is traditionally a measure of light sensitivity in film) nearly as easily as changing their flash settings or shutter speeds, and it can be done for each individual picture. Increasing digital ISO does often result in slightly grainier pictures, but can allow photography in very low-light conditions. The ease with which a digital camera can change its ISO is very helpful underwater, especially snorkeling; high ISO values may be too sensitive near the surface, but at 30' (9m) there is considerably less light and increasing the ISO is often necessary to take photos with ambient light. On my camera, I can do this quickly enough to still have the breath to compose and take my shot while free diving.

Changing white (color) balance - works better than filters
    Digital cameras also have the very valuable ability to adjust their white balance (WB, or sometimes called color balance). WB controls what the camera records as white, which is useful when the surrounding light is color-shifted. For example, indoor light is much redder than outdoor light (because light-bulbs are much cooler than the sun), and almost everything underwater will appear more blue than it truly is. Your eye corrects at the time, but photos reveal the true color. This can be corrected by setting the WB so that the camera adjusts all incoming light towards red (for underwater) or blue (for indoor). Doing so helps to restore the color often lost underwater by returning things the camera sees as pale blue to their proper white (and purple to red, etc.).

Digital, but not always still, cameras
    Another advantage of digital cameras is that nearly all of them have the capability to take short video clips. This site is not about underwater videography, which is a very different field, so I'll keep this short. There are times when a still photo just doesn't do the environment justice; a still shot of thirty feeding parrotfish is not nearly as impressive as an AVI (audio-video interlace, a common form of video file) video of them all swarming over the rocks and coral accompanied by the sound of dozens of beaks scraping up food. The video quality is sometimes poor (especially on less-fancy cameras), but it is still very nice to have the option.

Shutter delay (a downside)
    One scourge of digital cameras that should be mentioned is their shutter delay. Most film cameras can take a picture within a tiny fraction of a second of the shutter being pressed. Digital cameras, however, tend to take a significant fraction of a second which can completely spoil the composition of a perfectly prepared shot. The reason for this delay has to do with the way digital cameras focus and select light levels; the computer-controlled auto-focus and often relatively slow focus-adjust motors, plus the evaluative light processing algorithm, can result in a very noticeable delay between squeezing the button and capturing the image (which by that time has often changed, i.e. the fish swam out of view).
    There are three ways to avoid this problem: fancier and more expensive cameras, 'pre-shooting' the photograph during composition, and manually selecting all these settings. The first I will not go into except to say that digital camera manufacturers, well aware of this issue, have produced some very nice (and expensive) cameras with fast computers and lens motors; I would like to own one of these cameras but cannot presently afford to. As of 2015, several small rugged underwater cameras are indeed much faster than their precursors.
    The second solution, 'pre-shooting', requires more care in its use but is available on most cameras (digital and film; even some film cameras are slow). The idea is to get the camera to determine its focal range and light settings before you are ready to take the photo, so that when the composition is right you can capture the picture instantly. The mechanism for this is to aim the camera, then press the shutter button down halfway and hold it until you want to capture the shot, at which time the button is pressed the rest of the way. There are risks associated with doing this, however: you may squeeze too hard and inadvertently take a picture before you are ready, you may focus on the wrong distance (suppose the camera focuses on the background but the fish swims into the image halfway between you and that background), or the lighting may change such that the camera expects more or less ambient light and produces an underexposed or overexposed photograph. However, pre-shooting can be quite useful if you know how to make it work, and experimentation costs nothing but time.
    The third option is quite possibly the trickiest, as it requires skilled eyes to measure distance and light, and quick hands to change setting on the fly. However, such things are possible, and sometimes faster than the automated systems (especially on mid-range cameras). 'Point and shoot' cameras often do not allow this level of control, and high-class cameras are very likely both better and faster at measuring and adjusting than almost any human.

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