Digiscoping
Why Digiscope?
Definition
Digiscoping is the process
of taking photos with a digital camera, either still or video, through
a spotting scope.
Photography Alternatives
Until recently, the only way
to get photos of birds was to use a traditional film camera, either with
a long lens built for the camera, or by adapting the camera to a spotting
scope. With the advent of digital cameras and camcorders, and their vast
improvements in photo quality, many alternatives are now available. The
choice that is best for you will depend on how you want to use and display
the photos.
Digital vs. Film
Resolution is the amount of
information contained in an image. Film resolution is measured in line
pairs per millimeter, and is the result of the number of grains of silver
or chromatic dyes within the frame. In digital images, light is sensed
by a matrix of red, green, and blue sensors. A set of one of each color
sensor is called a picture element, or pixel. In digital still cameras,
the sensed image is stored on various kinds of memory chips; in digital
video cameras, images are usually stored on magnetic tape, though some
new cameras put images into a buffer, which is then written to a CD or
DVD disk. In either case, resolution is measured in pixels, or its larger
unit, megapixels (MP). The knock on digital used to be that it lacked
the resolution of film. This is no longer the case. Today's highest resolution
professional digital single lens reflex (SLR) cameras have more resolution
at 11 MP than 35mm film. At that resolution, you can make 4x5-foot posters
that look as good as film. At 5 MP, you can make 8x10 inch-prints that
are of film quality. If the final destination for the photo is a website,
a 3-MP camera will meet your needs.
Digital Benefits
- Store the equivalent of
15 rolls of film on a device the size of a quarter.
- Easily store your photos on your computer. No scanning
required.
- Ease of post-processing
- No processing mistakes
- Instant feedback - delete
bad photos immediately
- Lower cost per photo with
reusable flash memory
- Easier airline security check-in
Film Benefits
- Old familiar
- Lower battery requirements
Scopes vs. Long Lenses
Before addressing the relative
benefits here, we define magnification to facilitate comparison. In film
cameras, binoculars, and scopes, the "X" in the magnification rating means
"times normal". In film cameras, 50mm is considered normal, so a 400mm
lens would be 8X. In digital cameras and camcorders, the "X" means "times
the shortest focal length" or zoom range. Say two cameras claim 10X zoom
lenses. One has a wide-angle 35mm equivalent of 28mm while the other has
a 35mm wide-angle equivalent of 35mm. The maximum magnification on the
first camera is 10 x 28 = 280mm, which is 5.6X. The second camera goes
up to 350mm, which is 7X. For photographing scenery, the first camera
would be better. The second, while not really sufficient, would be better
for photographing birds.
Now we can compare scopes and
long camera lenses. Scope magnification ranges from 10X to 75X. In film
equivalence, this converts to 500mm - 3750mm. Film camera lenses used
by bird photographers are usually 600mm - 800mm, sometimes used with a
2X-telextender, thereby doubling that focal length. A 400mm f/2.8 lens
weighs over 10 lbs. A 600mm f/4 lens can weigh 15 lbs. These lenses gather
more light than scopes, but do so at enormous weight increases. The problem
is that to carry only one lens (and 2 would be a nightmare!), there is
no way to turn a large camera lens into a scope, and even at 1200mm, the
desired magnification isn't there. Simply put, to study birds as well
as photograph them, shooting through a scope is the way to go.
Built-ins vs. Components
Recently, some scope makers
have announced scopes with built-in digital cameras. While this is an
interesting solution, there are certainly some caveats. The only two scopes
that have built-in cameras so far have objective lenses in the 55mm to
60mm range. Scope views will not be of 80mm quality. Also, the digital
sensors have resolutions around 3.1 MP, which is on the small side. Worse,
to upgrade either the camera or the scope, you have to upgrade both. The
only advantage of having a scope with a built-in camera is that the camera
is ready to go faster than when you use separate parts.
Vignetting
Selecting a digital camera
for digiscoping is different than picking one for general use. Excluding
the professional digital SLR cameras, the best cameras for general use
have large objective lenses with large apertures. For digiscoping cameras,
however, large objective lenses lead to one of the biggest problems in
digiscoping - vignetting.
Vignetting is the effect caused
when the entire frame of the image is not illuminated, leaving a circular
image with surrounding black. It occurs when either the objective lens
of the camera is larger than the exit pupil of the scope, or when the
curvature or mounting of the objective lens of the camera is farther away
from the eyepiece of the scope than the scope's eye relief. For this reason,
most digiscopers prefer cameras with small objectives, which can be brought
very close to the scope's eyepiece. In general, pocket-sized digital cameras
with large zoom ranges are also problematic, as their zooming lens elements
recede from the eyepiece when zooming to larger magnifications.
The only way to solve the vignetting
problem without changing the physical parameters of the camera and scope
is to crop the image. Cropping can be done in a photo-editing program,
which reduces the size of the image, or by zooming in with the camera
while taking the photo. Zooming in maintains full resolution of the image
file, but lowers image brightness.
Mating Cameras to Scopes
Before digiscoping, people
shooting through scopes attached SLR cameras to scopes using special adapters
that used the camera's lens mount and a tube that connects the camera
to the scope's eyepiece socket. The limitation here is that there is no
ability to zoom either the scope or the camera.
In the beginning of digiscoping,
everybody just held the digital camera up to the scope's eyepiece. This
has speed advantages, but photos taken this way could be blurry due to
camera shake. Soon, camera-to-scope mating devices began appearing in
the field. Now, scope makers are designing them for their scopes. To accommodate
the wide variety of digital cameras around, these tend to be collars that
mount to the eyepiece and accept cameras with adapter plates that screw
into the filter thread on the camera's lens. Thus, for a camera lacking
a filter thread, you need another solution. The other problem with this
mounting system is that it isn't good for camcorders, which weigh much
more than still cameras. You certainly do not want to hang a 1.5-lb weight
to a scope eyepiece.
The solution to this
is a mounting bracket design that supports cameras without filter threads
and can be adjusted to align the axis of the eyepiece to the axis of the
camera lens. Three scope makers, Kowa, Nikon, and Zeiss offer brackets
that mount between the scope and the tripod. These have vertical and horizontal
adjustments that facilitate alignment. Each has its own method for adapting
to straight and angled scopes. The Kowa and Nikon brackets will fit most
scopes and cameras, but the Zeiss bracket is less adaptable. Swarovski,
and now Kowa, have brackets that mount directly to the scope body. These
are designed to swing into place behind the eyepiece and then swing back
out of the way when the camera is not in use. With the exception of the
new Kowa TSN-DA4, none of the brackets allow for shooting a vertical format
photo as the collar-type systems do, although with the Swarovski DCB you
can achieve the same result by rotating the scope. Since birds do not
wait to pose, setup time is of the essence. Get a mount system that deploys
quickly.
A more recent technique involves
holding a digital SLR up to the eyepiece. To avoid vignetting, you must
use a 50mm lens and only zoom with the scope eyepiece. It might seem that
this will also work with film SLRs, but the circle of illumination is
not large enough to cover a 35mm frame.
Digital Film (Memory)
Digital movie film is magnetic
videotape. It comes in two sizes: Digital 8, which is the same size as
standard 8mm videotape, and MiniDV, which is a smaller cassette. Both
hold the same amount of data. Digital 8 costs less while MiniDV is about
half the size and therefore easier to carry.
Digital still film is a memory
chip generically known as removable flash memory. These chips come in
various shapes, sizes, and capacities. Older forms include SmartMedia
(SM), Compact Flash (CF), and Sony Memory Sticks. SmartMedia is becoming
obsolete, Sony Memory Sticks are proprietary (only used by Sony products),
but Compact Flash is still going strong. Some reasons for the strength
of CF is it has the largest capacities - up to 2GB, are increasing write
speeds with the same interface, and it is compatible with IBM MicroDrives
(miniature hard drives that fit in a CF slot) which now go up to 4GB.
New forms of memory media include Secure Digital, Reduced-size MultiMediaCard,
and xD-Picture Card. Each of these new formats is aimed at smaller size
and faster memory transfer. Some of the new formats have adapters to allow
them to fit into older cameras and card reading adapters. When purchasing
your camera, check out the current prices and capacities of flash memories
and make sure the camera is compatible with the type you want.
Most cameras accept one or
two types of flash memory. One of the decisions upon which to base a camera
purchase is the type of flash memory you want to use, which may be based
on the number of photos it can store. When comparing prices, divide the
price by the memory size to get the price per MB. Frequently, the highest
capacity cards are not as cost effective as the next size down. The number
of images your flash memory can hold depends on its capacity, the resolution
of your image file, the file type, and the amount (if any) of compression
with which the file is stored.
Batteries
Digital cameras require a lot
of power. Most digital cameras use AA batteries, so your choice is just
of which kind to get. The only two real alternatives are Nickel Metal
Hydride (NiMH) and Lithium Ion rechargeables. Use of alkaline batteries
is discouraged for several reasons. First is that some cameras will not
work with them. But more importantly, they are both the most expensive
and the most polluting. With rechargeable batteries you will get hundreds
of repeat uses instead of the one shot with alkalines. And, even if alkalines
could be used for as long a period as the rechargeables, they contain
10 times as much polluting chemicals as either of the rechargeables. As
birders who should be concerned with conservation of habitat, this should
be a deciding factor even if all the other factors were equal. To determine
how long a battery will last, look at the battery's power rating, which
is measured in milliamp-hours (mAh). The higher the number, the longer
the battery will last on a single charge. Current longest-lasting AA NiMH
batteries are rated at 2600mAh.
Shooting Techniques
Composing
Most digital cameras have two
ways of composing an image - the viewfinder and the LCD screen. On many
small digital cameras, however, the viewfinder does not provide a through-the-lens
(TTL) view, and is useless in composing the image or in focusing. For
these cameras, you will need to use the LCD screen on the back of the
camera. Since these screens can be difficult to see in bright light, viewing
hoods have been designed to help. A less expensive (and perhaps even better)
alternative is to use a plastic slide viewer that can be trimmed of the
slide holder and placed over the LCD. These slide viewers have 2x lenses
that can also aid in seeing the LCD for focusing purposes. If you would
rather use the viewfinder, you will need to get a camera with a TTL or
direct electronic viewfinder.
Focusing
This is one of the trickiest
parts of digiscoping. Theoretically, an autofocus camera should be able
to compensate for a slightly unfocused image projected by the scope and
produce a sharply focused image. But, because the camera is not all that
easy to place at the focal point of the scope, a different technique is
often used. What many people do is to set the camera to focus on infinity,
and then to manual focus. Then, using the scope's focusing knob, get the
best focus possible. Finally, turn the autofocus back on and let the camera
do the ultimate fine-tuning.
Metering
In general, you should be able
to use autoexposure (AE) most of the time. As long as you have average
scenes with average subjects, any exposure mode will do. Often, spot metering
will produce a good exposure. However, when your subject is a Great Egret
or a Great-tailed Grackle, you will need to compensate to get a properly
exposed image. If you're not sure of your exposure, you can always bracket,
delete the shots that don't work, and choose the best exposure for the
rest of your shots.
Zooming
In optical zoom mode, the camera
records all the pixels in the sensor. The camera's lens resizes the image.
In digital zoom, however, the camera records only a portion of the pixels
in the sensor (cropping into the image), resizes the image back to full
size, and then interpolates the image data to approximate what the interstitial
pixels would be. You can perform this process in your image editing software
much better than the camera can do it. We recommend that you turn off
digital zoom, forget it's there, and never use it.
When digiscoping, zoom the
camera, not the scope. Leave the scope at minimum zoom. When you zoom
the scope, you reduce the exit pupil of the scope, which reduces the light
reaching the camera, and you increase the vignetting. Zooming the camera
improves vignetting and keeps the exit pupil of the scope constant.
Selecting a Spotting Scope
As previously discussed, the
optimum digiscoping scope has a big objective lens with high quality glass.
With one of the new 65m scopes, the high quality glass is even more important.
This is not to say that good photos are unobtainable with smaller scopes,
but it is more difficult and the quality will be lower.
For those who want the flexibility
to build their digiscoping system with complete freedom in their camera
choice, it might be best, at least for now, to select a scope from a manufacturer
that doesn't make cameras. At this writing, except for the universal mount
system brackets mentioned above, most companies that make both scopes
and cameras make digiscoping adapters that only fit their own cameras.
Be sure to investigate compatibility issues before you buy.
Selecting a Digital Camera
As more people have tested
more cameras for digiscoping, the perception of what works best has changed.
We now know that cameras with large optical zooms tend to have more vignetting
problems, as do cameras where the zooming lens element moves away from
the subject when going to larger magnification. For best results with
point-and-shoot cameras, look for cameras that do not exceed 4x optical
zoom, or that have internal zoom elements.
A common problem with early
digital cameras that is improving with newer cameras is a delay between
the time that you press the shutter button and the time the camera takes
the photo. If this is too long, you can lose the bird.
Older cameras took a long time
to write the image file to memory. Newer designs can not only write quickly,
but also shoot several shots rapidly (known as burst mode).
Digiscoping systems (camera,
scope, and tripod) are inherently susceptible to vibrations. These can
result from wind or hand shake, and are worsened at increasing magnifications.
The best way to avoid these is to use a remote camera shutter release.
Some cameras are capable of accepting an electronic cable release. Others
have wireless remotes. Finally, some digiscoping adapters, such as the
Kowa TSN-DA4 allow use of an old-style mechanical cable release that is
placed over the shutter button by an adjustable positioning arm. Electronic
cable releases are the best solution. Wireless remotes often have a built-in
delay of up to three seconds.
Some characteristics of cameras
good for digiscoping are:
- 3x - 4x optical zoom
- External zoom elements
- Lenses with filter threads
- Minimum 3-MP sensor - more is better
- LCD screens that swivel independently from the lens
- Flash memory slot
- Full manual capability
- Fast write speed
- Little or no shutter lag
- Cable or wireless shutter release
For a list of digital cameras
that do not vignette or can eliminate vignetting by use of the optical
zoom, see this list compiled by Roy Halpin of Swarovski and Jeff Bouton
of Leica.
Post Processing
One of the biggest benefits
of digital photography is the ability to edit image files on a computer.
Exposure and contrast, color saturation, image sharpness and background
alteration can all be improved after taking the photo. You can even remove
branches that block part of the bird. Artistic effects, copyright notices,
watermarks, captions, photographic data, and just about anything else
can be added. Digital videos can also be edited to add various types of
scene changes like fades, cuts, and other fancy effects seen on TV. Video
frames can be converted to stills.
Reference Material
These three articles, written
by Clay Taylor of Swarovski, give an excellent overview of the current
state of the art in digiscoping.
Conclusions
- Digiscoping offers a quality
image using lighter and less expensive equipment than film
- Better scopes give better
photos
- Mount systems give sharper
photos than hand-holding and leave your hands free to focus and shoot.
- NiMH batteries are the cheapest
and the most environmentally friendly
- Get the largest economical
size flash memory available for the camera
- Bracket the exposure, take
the photo, view it, then correct if necessary
- Photo editing programs let
you correct a multitude of problems.
- When you are unsure of a
proper exposure, take the photo, view it, then correct if necessary
- Photo editing programs let
you correct a multitude of problems.
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