TELESCOPES, OPTICS and ASTROPHOTOGRAPHY

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TELESCOPES, OPTICS and ASTROPHOTOGRAPHY
A Power Point Presentation by Stan
Celestian Instructor of Astronomy, Geology and
Physical Science at Glendale Community College
In viewing this presentation the symbol () will
appear. It is your signal to advance to the next
image. ()
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TELESCOPE OPTICS
The emphasis of the presentation is

• The Schmidt Cassegrain Telescope
• The Optical Path through the Telescope
• Eyepieces and Magnification

This Power Point Presentation is followed by
digital images of the Moon and the techniques of
ASTROPHOTOGRAPHY ()
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The Schmidt Cassegrain Telescope
Finder Scope ()
Tube()
Declination Circle
Eyepiece ()
Fork Mount ()
Diagonal ()
INSIDE

Counter Weights ()
11 inch Celestron Schmidt Cassegrain ()
Clock Drive ()
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Parts of the 11 inch Celestron Schmidt Cassegrain
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Parts of the 11 inch Celestron Schmidt Cassegrain
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Parts of the 11 inch Celestron Schmidt Cassegrain
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11 inch Celestron Schmidt Cassegrain ()
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The Schmidt Cassegrain Telescope

Corrector Plate
This clear almost flat piece of glass that covers
the open end of the tube, serves two functions.
First it holds the secondary mirror in place and
second its slight curvature spreads the light
onto the primary mirror. ()
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LIGHT PATH FOR THE SCHMIDT CASSEGRAIN
The light passes through a hole in the primary
mirror. ()

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The Schmidt Cassegrain Telescope

FINDER SCOPE
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The Schmidt Cassegrain Telescope

Focus Knob
The focus of the telescope is accomplished by
moving the primary mirror forward or backward.
Eyepiece in Diagonal
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The Schmidt Cassegrain Telescope

This is the Right Ascension circle. It is like
the projection of longitude onto the sky.
Inside the base of the telescope is the clock
drive. When properly aligned, it allows the
telescope to track objects across the sky.
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Polaris ()
This view is along the axis of the telescope. To
properly align the telescope the axis of the
mount points towards the North Star Polaris.
()
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This is a simple technique of taking astrophotos
with a digital camera. ()
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Following are pictures of the 1st quarter phase
of the Moon. The pictures were obtained by
simply holding the lens of the camera over the
eyepiece of the telescope. 20 October 2004
Certainly there are problems in doing this type
of photography but it is simple, quick and
produces results of sufficient quality to allow
identification of lunar features. ()
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Northern Terminator ()
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Southern Terminator ()
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Southern Area ()
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Central Area ()
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Central Area ()
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Comparison of images taken with different focal
lengths. ()
Notice the greater magnification obtained with
the shorter focal length eyepieces. ()
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For longer exposures (greater than 30 seconds),
the camera is mounted on the telescope. This
allows the camera to move with the telescope and
track the subject across the sky to prevent
blurring the image. ()
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TELESCOPE EYEPIECES Eyepieces can change the
magnification and field of view of the telescope.
Note the small diameter lens of the 6 mm
eyepiece compared to the larger diameter lens of
the 16.8 mm eyepiece. The small diameter of the
6 mm eyepiece does provide higher magnification
(see next slide) but at a cost. The image will
be dimmer because of the smaller lens and the
field of view will be smaller. ()
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TELESCOPE EYEPIECES Note the small diameter lens
of the 6 mm eyepiece compared to the larger
diameter lens of the 16.8 mm eyepiece. ()
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TELESCOPE EYEPIECES
The MAGNIFICATION of a telescope is determined by
the focal length of the objective (the primary
mirror in the Schmidt Cassegrain) and the focal
length of the eyepiece. The formula is ()
FOCAL LENGTH OF THE OBJECTIVE
MAGNIFICATION
divided by
FOCAL LENGTH OF THE EYEPIECE ()
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TELESCOPE EYEPIECES
As an example, take this Schmidt Cassegrain
telescope. It has a focal length of 3400 mm.
With a 6 mm eyepiece the magnification would be
()
567 X
()
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End of Telescope Optics
()
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ASTROPHOTOGRAPHY

• Presented by
• Stan Celestian
• Instructor of
• Astronomy, Physical Science and Geology at
• Glendale Community College

()
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ASTROPHOTOGRAPHY

• WHAT YOU NEED

CAMERA ()
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ASTROPHOTOGRAPHY

• WHAT YOU NEED

A critical component of a camera for
astrophotography is the ability of the shutter to
stay open for long periods of time. In this type
of photography exposures will normally last at
least 30 seconds. ()
There must be a B (for bulb) setting on the
camera. When the camera is set to the B
setting the shutter will remain open as long as
needed. Many automatic cameras do not have a B
setting. ()
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ASTROPHOTOGRAPHY

• WHAT YOU NEED

CABLE RELEASE ()
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ASTROPHOTOGRAPHY

• WHAT YOU NEED

The purpose of the cable release is to avoid
vibrations. When taking a picture you normally
just push the button on the top of the camera.
With the cable release attached to this button an
exposure is made by depressing the plunger at the
end of the cable release. ()
Most cable releases have a locking mechanism that
allows for making long exposures without the need
of the photographer holding the cable release.
Simply push the plunger down to engage the lock
and push a ring to release it. ()
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ASTROPHOTOGRAPHY

• WHAT YOU NEED

TRIPOD ()
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ASTROPHOTOGRAPHY

• WHAT YOU NEED

A tripod means stability. During a long 30
second exposure any movement of the camera will
mean blurred images. A tripod is the best way to
hold the camera steady for these long periods of
time. ()
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ASTROPHOTOGRAPHY

• WHAT YOU NEED

FILM ()
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ASTROPHOTOGRAPHY

• WHAT YOU NEED

There are many good films available for
astrophotography. The example shown here
Kodaks Gold MAX 800 is a good choice for making
color prints. It has a high speed (800 ASA) and
is fairly fine grained for a fast film. In
addition, it records accurately the various
colors of the dim objects you may want to
photograph. Other good films can be used. Ask a
photo dealer for advice. ()
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ASTROPHOTOGRAPHY

• CAMERA FUNCTION

The B stands for Bulb. ()
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ASTROPHOTOGRAPHY

• CAMERA FUNCTION

This is the B setting on the camera. In the
old days a photographer would squeeze a bulb to
open the shutter. When the pressure on the bulb
was released, the shutter would close. Cameras
no longer have a bulb but they still have a B
setting. ()
This is the setting that can provide long
exposures. The other numbers refer to fractions
of a second for the shutter time. For example
the 1 is actually 1/1 (one second) the 2 is ½
(half second) the 4 is ¼ (quarter of a second)
and so on. ()
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ASTROPHOTOGRAPHY

• CAMERA FUNCTION

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ASTROPHOTOGRAPHY

• CAMERA FUNCTION

This is the focus ring of the cameras lens. The
red arrow is pointing at the setting for
infinity. This is where the focus needs to be
set for astrophotography. ()
Focus Ring
Be sure to check the focus of the lens before
each picture. Because astrophotos are taken in
the dark, it is easy to miss this very important
setting. ()
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ASTROPHOTOGRAPHY

• CAMERA FUNCTION

Aperture Setting ()
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ASTROPHOTOGRAPHY

• CAMERA FUNCTION

The last adjustment to make is the opening of the
lens. Most lenses use an iris diaphragm to
control the amount of light reaching the film.
You may think that the wide open setting 1.4
(letting the most light in) would be the best for
dim astronomical objects. ()
This is called shooting with the lens wide
open. ()
But most lenses have some sort of irregularities
and the light that comes to a focus from the edge
of the lens tends to create a problem called
coma. Coma is a distortion of the image at the
edge of the field of view. ()
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ASTROPHOTOGRAPHY
Notice the flare of this bright star at the edge
of the field of view. This is coma. ()
This is a close up view. ()
Taurus Glendale, AZ
Aldebaran
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ASTROPHOTOGRAPHY
The Effect of Focal Length
The net effect of the focal length of the
objective (lens or mirror) is to moderate the
magnification of the system camera or
telescope. ()
The following example shows how magnification is
related to the focal length of the objective.
The images are of a weather balloon located over
the greater Phoenix area. Basically, the greater
the focal length, the greater the magnification.
()
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ASTROPHOTOGRAPHY
The Effect of Focal Length
Weather Ballon
This little white dot.
52 mm A 52 mm lens is considered no magnification
it is similar to what a person with normal
vision would see. ()
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ASTROPHOTOGRAPHY
80 mm Slight Magnification ()
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ASTROPHOTOGRAPHY
2000 mm ()
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ASTROPHOTOGRAPHY
3400 mm ()
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ASTROPHOTOGRAPHY
This is the view through a telescope. Obviously
there is significant magnification. BUT also
notice that the field of view was dramatically
decreased. Another aspect of an increase of
focal length is a reduction of the field of view.
()
3400 mm
The rectangle in the image on the left shows the
approximate field of view for 3400 mm telephoto
image. This is a very small window to the sky
but one that is magnified. ()
The instrument package hanging from the bottom of
the balloon is about the size of a refrigerator.
It is a cosmic ray detector. ()
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ASTROPHOTOGRAPHY

• READY
• TO
• GO

An important consideration in producing good
astrophotos is to minimize the effect of city
lights (called light pollution or skyglow). The
best astrophotos are achieved under very dark
skies. Darker skies will reveal many more stars
and there will be a significant increase in
contrast, i.e., the background will be darker
thus making the stars stand out. ()
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ASTROPHOTOGRAPHY
This picture of the camera on the tripod with the
cable release attached, shows the setup used to
take the following pictures. ()
The other important factor is that the locality
is not in a city it is out in the desert far
from city lights. ()
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ASTROPHOTOGRAPHY
Buckeye Hills Regional Park, Arizona A nice
quiet, dark place to go. It is located just west
of Phoenix. ()
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ASTROPHOTOGRAPHY
Taking astrophotos is not unlike taking normal
photos composition is important. Here the Moon
and Jupiter are the center of attention but the
palm tree has a grounding effect - it provides
a reference for the picture. It is always nice
to have a foreground object in your
non-magnified your photos. ()
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ASTROPHOTOGRAPHY
Moonrise near Rocky Point, Mexico ()
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ASTROPHOTOGRAPHY
Kitt Peak, Arizona ()
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ASTROPHOTOGRAPHY
Jupiter
Venus
Because the layout of the solar system is fairly
flat, the planets and even our Moon do not stray
very far from the ecliptic. This often produces
good opportunities for groupings in the night
sky. ()
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ASTROPHOTOGRAPHY
Orion
This is what you can expect with a camera on a
tripod. This is a 30 second exposure of the
constellation Orion. A lot of interesting
objects are visible. ()
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ASTROPHOTOGRAPHY
Orion
Belt
Rigel
Betelgeuse
Sword ()
30 second exposure with Extachrome 400
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ASTROPHOTOGRAPHY
Why only 30 second exposures? With a normal 50
55 mm lens the exposure is limited to 30 seconds
because the Earth is spinning on its axis.
Longer exposures will cause the stars to be drawn
out into lines. These are called star trails. ()
The next photo shows the result of a longer
exposure. The camera is on the tripod with the
speed of the shutter set at B, the shutter is
being held open with the cable release and the
exposure time is 14 minutes. ()
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ASTROPHOTOGRAPHY
Orion
Orion Nebula
()
14 minute exposure with Extachrome 400
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ASTROPHOTOGRAPHY
You can see that the spin of the Earth is a
problem with prolonged exposures. If you use a
longer focal length lens (100 mm) the effect is
greater and you would have to use a shorter
exposure to prevent star trails. However,
sometimes the effect can be welcomed. If, for
example, you wanted to catch the spin of our
planet you might photograph star trails around
Polaris the Pole Star (North Star). Because
the spin axis of the Earth points in that
direction, Polaris would remain stationary and
all of the other stars would trail around
Polaris. ()
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ASTROPHOTOGRAPHY
You can see that Polaris is not exactly lined up
with the spin axis of the Earth, but it is close.
()
Star Trails Around Polaris
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ASTROPHOTOGRAPHY
This is another picture of Orion. But this time
there are many more stars and other objects
recorded by the film. This is an exposure of 3
minutes, but without star trails This is achieved
by having the camera track Orion across the sky
during the exposure. The easiest way to do this
is to attach the camera to a telescope that has a
clock drive. In this way long exposures can be
made. The next slide identifies some of these
objects. ()
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ASTROPHOTOGRAPHY
Betelgeuse
Rosette Nebula ()
The Great Orion Nebula
Horse Head Nebula
Rigel
Orion
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ASTROPHOTOGRAPHY
This is the set up for longer exposures. The
camera is attached to the telescope. It is
called a piggy back attachment. The telescope
is simply acting as the mount. As the telescope
tracks the object across the sky, the camera also
tracks the object. ()
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ASTROPHOTOGRAPHY
Sirius
Canis Major
This is a 3 minute exposure of Canis Major. ()
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ASTROPHOTOGRAPHY
4 Minute exposure ()
The Pleiades
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ASTROPHOTOGRAPHY
This is a 30 second exposure with the camera on a
tripod. The saguaros were illuminated during the
exposure with a flash light. The photograph was
made at the White Tanks Regional Park just west
of Phoenix. ()

Comet Hale Bopp ()
March 1997
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ASTROPHOTOGRAPHY
Gas Tail ()
Dust Tail ()

Direction to the Sun ()
Comet Hale Bopp 4 minute exposure Camera was
piggy backed on telescope. 500 mm lens ()
April 1997
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ASTROPHOTOGRAPHY

Ikeya-Zhang 3 Minute Exposure March 2002 Camera
was piggy backed on telescope. 500 mm lens ()
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ASTROPHOTOGRAPHY
The Horsehead Nebula Camera was piggy backed on
telescope. 500 mm lens ()

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ASTROPHOTOGRAPHY
What could possibly go wrong?

Things that go bump in the night. ()
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ASTROPHOTOGRAPHY

Whats wrong with this picture?... A couple of
things ()
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ASTROPHOTOGRAPHY
First of all, this is actually two pictures. In
normal photographs there is a black line that
separates one frame from another. The film is
loaded into a machine that looks for this black
line. When it finds it the machine simple counts
the sprockets on the side of the film to make a
cut. Obviously in astrophotography the black
line does not show up. In this case the machine
randomly made a cut. It was not in the right
place. (Advance one frame to see where the line
is located.) ()

()
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ASTROPHOTOGRAPHY

The second problem is that the star images are
blurred. In fact the image on the left has check
marks instead of stars. This was caused by
bumping the tripod while the photo was being
made. ()
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ASTROPHOTOGRAPHY
The Wrong Place
Good astrophotos are made far from the influence
of city lights. In this photo of Mars and Venus
setting in the west, a car drove up during the
exposure note the bright headlights in the
bottom right. In addition, an airplane turned on
its landing lights as it made its approach to Sky
Harbor in Phoenix. ()
A I r p l a n e
It would be better to find a more remote
location. ()

C a r
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ASTROPHOTOGRAPHY
STAR TRAILS AROUND POLARIS
This would have been a great picture. It is a 4
hour exposure of Polaris with extensive star
trail (Earths rotation). However, it had been
so long since I started the picture that I forgot
about it. The bright streak across the center is
my flashlight checking on the camera. ()

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ASTROPHOTOGRAPHY
?

This is a 30 minute exposure of the Pleiades in
the constellation Taurus. The camera was riding
piggyback on the telescope and I knew it was
pointed in the right direction. BUT I never
looked through the view finder of the camera. I
left the lens cap on! ()
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ASTROPHOTOGRAPHY
THE END