National Geographic NG90EQ Telescope User Manual


 
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The two eyepiece ports can be used in another way. With an optional camera adapter
and appropriate T-ring a 35-mm SLR camera body can be attached to the rear eyepiece
port. The 45º diagonal prism must first be removed. With an eyepiece in the top
eyepiece port and a camera body attached to the rear eyepiece port a subject can be
observed with the eyepiece. Then by simply adjusting the flip mirror, a picture can be
taken through the rear eyepiece port.
FOCUSING FOR ALL VIEWING IS ACCOMPLISHED BY SLOWLY TURNING THE
RUBBERIZED WHEEL LOCATED AT THE RIGHT REAR OF THE MAIN OPTICAL
UNIT. IF THE IMAGE SEEN IN THE EYEPIECE IS IN FOCUS, THE IMAGE SEEN BY
THE CAMERA WILL ALSO BE IN FOCUS.
ABOUT MAGNIFICATION
The magnification power of a telescope indicates how much an image is enlarged or
how big and close it appears to the viewer. The focal length of the eyepiece, combined
with the focal length of the telescope, determines the magnification power. To calculate
the power of your telescope with any particular eyepiece, simply divide the focal length
of the telescope (1,200 mm) by the focal length of the eyepiece (indicated in “mm” on
the eyepiece collar).
Example: 1200-mm focal length (tube) = 48X magnification power
25-mm focal length (eyepiece)
The following magnification values are achieved when using the Barlow lens and the
interchangeable eyepieces:
Eyepiece Power Power With 3X Barlow Lens
25 mm 48X 144X
9 mm 133X 400X
Higher magnification powers can be achieved by using the included 3X Barlow lens.
The 3X Barlow lens is inserted between the telescope and the eyepiece. In Fig. 20 it is
shown being used at the rear eyepiece port. It can be used at either eyepiece port.
(Fig. 20)