New Possibilities for Long Distance Video
Imaging with the 2Plus LE-Adapter
by Kenneth Farmer, PhD
The new 2Plus LE-Adapter
from LensPlus (www.ccfabuja.org)
significantly expands the possibilities for long distance video using
telescopes. The 2Plus permits the coupling of telescope eyepieces to
digital cameras and video cameras for "afocal projection" imaging. In
afocal projection, the camera records the image projected by the
eyepiece for dramatic close-ups of terrestrial or astronomical scenes.
The new 2Plus will
accommodate eyepieces up to 60mm in diameter. This is important for two
reasons: (1) Larger eyepieces offer brighter images. This is crucial for
ultra-telephoto video, because as focal length increases, light reaching
the CCD decreases. (2) Larger eyepieces decrease the tendency for
vignetting (darkening of the edges of the image) when used with digital
cameras and camcorders.
The precision machined
2Plus has unique easy-to-use thumb-screw mounts for attaching the
adapter to the barrel of the eyepiece. With the eyepiece centered and
securely mounted in the adapter, the camera or camcorder is then
threaded onto the 2Plus using its 37mm threads. Step-down or step-up
adapter rings can be used as needed for attaching cameras with filter
sizes other than 37mm. The example below shows the dramatic long
distance imaging that can be achieved using the 2Plus LE-Adapter.
Afocal Projection with the 2Plus LE-Adapter
In the image below, the
2Plus is shown coupling a large 32mm TeleVue Plossl eyepiece in a Meade
ETX to a Panasonic DV400 camcorder. The arrow shows the location of an
athletic track two miles in the distance. The bottom two images
show runners on the track as captured by the camcorder. The images of
the runners have not been digitally enlarged. This incredible optical
magnification is achieved by using the 2Plus for afocal projection.
Calculating System Focal Length
In afocal projection
imaging, total system focal length is calculated by multiplying the
focal length of the digital camera or camcorder by the magnification
factor of the telescope. Expressed in terms of an equivalent 35mm camera
lens, the DV400 camcorder has a maximum optical focal length of
approximately 700mm. The Meade ETX telescope (which has a 1250mm focal
length) is equipped with a 32mm TeleVue Plossl eyepiece. Telescope
magnification is determined by dividing the focal length of the
telescope by that of the eyepiece being used. The system focal length
for the DV400 / ETX combination length is therefore calculated as
follows:
1250mm/32mm X 700mm =
27,343mm
The system focal length
is equivalent to a whopping 27,000mm lens on a 35mm camera! Two
averaged-sized runners fill almost the entire vertical field of view at
a distance of 2 miles.
Conclusion
The 2Plus LE-Adapter
opens up a host of new possibilities for the camcorder and digital
camera enthusiast who wants to capture extreme long distance images
using their favorite telescope, spotting scope or even binoculars. The
2Plus has the look and feel of a high quality optical accessory right
out of the box. A mounting arm for the adapter can be connected to the
tripod mount on the camera for additional support if needed.
Kenneth Farmer is author
of the "Extreme Camcorder Handbook" on infrared and ultra-telephoto
imaging with camcorders. His company website is
www.infraredvideo.com.
