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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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