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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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