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Celestron C4.5 User Manual

Celestron C4.5
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Calculating
Magnification
Determining
Field
of
View
|24
©
Getting
Started
You
can
change
the
power
of
your
Celestron
C4.5
just
by
changing
the
eyepiece
(ocular).
To
determine
the
magnification
for
your
C4.5,
simply
divide
the
focal
length
of
the
telescope
by
the
focal
length
of
the
eyepiece
you
are
using.
In
equation
format,
the
formula
looks
like
this:
Focal
Length
of
Telescope
(mm)
Magnification
=
———
———————————————————
Focal
Length
of
Eyepiece
(mm)
Let's
say,
for
example,
that
you
are
using
a
12.5mm
eyepiece.
To
determine
the
magnification,
simply
divide
the
focal
length
of
your
C4.5
(900mm)
by
the
focal
length
of
the
eyepiece
(12.5mm).
This
yields
a
magnification
of
72
power.
Although
the
power
is
variable,
each
instrument
—
under
average
skies
—
has
a
limit
to
the
highest
useful
magnification.
The
general
rule
is
that
60
power
can
be
used
for
every
inch
of
aperture.
For
example,
the
C4.5
is
4.5"
in
diameter.
Multiplying
4.5
by
60
gives
a
maximum
useful
magnification
of
270
power.
Although
this
is
the
maximum
useful
magnification,
most
observing
is
done
in
the
range
of
20
to
35
power
for
every
inch
of
aperture
which
is
90
and
135
times
for
the
C4.5.
Determining
the
field
of
view
is
important
if
you
want
to
get
an
idea
of
the
angular
size
of
the
object
you
are
observing.
To
calculate
the
actual
field
of
view,
divide
the
apparent
field
of
the
eyepiece
(supplied
by
the
eyepiece
manufacturer)
by
the
magnification.
In
equation
format,
the
formula
looks
like
this:
Apparent
Field
of
Eyepiece
True
Field
=
Magnification
As
you
can
see,
before
determining
the
field
of
view
you
must
first
calculate
the
magnification.
Using
the
example
we
started
with
above,
we
can
deter-
mine
the
field
of
view
using
the
same
12.5mm
eyepiece.
The
12.5mm
Ultima
eyepiece
has
an
apparent
field
of
view
of
51°.
Divide
the
51°
by
the
magnifi-
cation,
which
is
72
power.
This
yields
an
actual
field
of
0.7°,
or
almost
three-
quarters
of
a
degree.
This
formula
gives
you
the
true
field
of
view
in
degrees.
To
convert
degrees
to
feet
at
1,000
yards,
which
is
more
commonly
used
for
terrestrial
viewing,
simply
multiply
by
52.5.
Continuing
with
our
example,
multiply
the
angular
field
of
.7°
by
52.5
produces
a
linear
field
width
of
36.7
feet
at
a
distance
of
one
thousand
yards.
The
apparent
field
of
each
eyepiece
that
Celestron
manufactures
is
found
in
the
Celestron
accessory
catalog
(#93685).

Table of Contents

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Celestron C4.5 Specifications

General IconGeneral
BrandCelestron
ModelC4.5
CategoryTelescope
LanguageEnglish

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