National Geographic NG90EQ About Magnification, Eyepiece, Power With 3X Barlow Lens

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)

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