SAXON 1026AZ3 SC REFRACTOR TELESCOPE INSTRUCTION MANUAL
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Using the Barlow Lens
A Barlow is negative lens which increases the magnifying power of
an eyepiece, while reducing the field of view. It expands the cone of
the focused light before it reaches the focal point, so that the
telescope’s focal length appears longer to the eyepiece.
The Barlow is usually inserted between the diagonal and the
eyepiece. With some telescopes, it can also be inserted between
the focuser and the diagonal, and with this position it gives even
greater magnification. For example, a Barlow which is 2x when
inserted after the diagonal can become 3x when placed in front of
the diagonal.
In addition to increasing magnification, the benefits of using a Barlow lens include improved eye
relief, and reduced spherical aberration in the eyepiece. For this reason, a barlow plus a lens
often outperform a single lens producing the same magnification. However, its greatest value
may be that a barlow can potentially double the number of eyepiece in your collection.
Focusing your telescope
Slowly turn the focus knobs under the focuser, one way or the
other, until the image in the eyepiece is sharp. The image
usually has to be finely refocused over time, due to small
variations caused by temperature changes, flexures, etc. This
often happens with short focal ratio telescopes, particularly
when they haven’t yet reached outside temperature. Refocusing
is almost always necessary when you change an eyepiece or
add or remove a Barlow lens.
Operating your telescope #2
