SKY-WATCHER ESPRIT 120 ED Super APO User manual

1
INSTRUCTION MANUAL
ESPRIT 120 ED Super APO
Copyright © Sky-Watcher
ES120-F-141120V2-EN

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Table of contents
Table of Contents
Introduction........................................................................................................................................ 2
Getting started................................................................................................................................... 3
Parts description.................................................................................................................................. 3
Unpacking the telescope.....................................................................Error! Bookmark not defined.
Preparing the telescope for an observation.......................................................................................... 3
Cooling the telescope .......................................................................................................................... 4
Aligning the finder scope.................................................................................................................... 5
Using the telescope for visual observation............................................................................ 6
Inserting the eyepiece.......................................................................................................................... 6
Focusing.............................................................................................................................................. 6
Using the telescope for prime focus imaging....................................................................... 7
Installing the field flattener and a DSLR (Digital Single-Lens Reflex) camera.................................. 7
Installing a 48mm filter inside the focal extender............................................................................... 8
Installing the field flattener and a CCD (Charge-Coupled Device) camera........................................ 8
Installing the field flattener and a CCD camera - continued............................................................... 9
Focusing.............................................................................................................................................. 9
Framing the picture ............................................................................................................................. 9
Useful tips for all observations................................................................................................ 10
Removing the finder scope................................................................................................................ 10
Using the indexed scale..................................................................................................................... 10
Rotating the focuser........................................................................................................................... 10
Specifications.................................................................................................................................. 11
Telescope specifications.................................................................................................................... 11
Threads specifications........................................................................Error! Bookmark not defined.
Different releases: The Helinear Focuser.......................................................................... 122
Focusing with the Helinear focuser................................................................................................. 122
Before doing prime focus imaging.................................................................................................. 122
Framing a picture with the Helinear focuser................................................................................... 122

2
Introduction
The spirit of perfection, by Sky-Watcher
Designed with the discerning astronomer in mind, Sky-Watcher top-of-the-line Esprit refractors
deliver the kind of imaging performance one would expect from telescopes costing much more. With
their three-element air spaced objective lens design, false color is completely eliminated, yielding
exceptional contrast and sharpness.
The 3" CNC machined 1:11 rotatable dual speed linear power focuser provides a smooth, rock-solid
focusing with zero image shifts. The Esprit ED 120mm refractor comes with a 9 x 50 right angle
finder scope, 2-inch Star diagonal, D-style dovetail, eyepiece, retractable dew cap and padded case.
Everything you need to get out under the stars.
The 2-element thread-on 48mm field flattener guarantees excellent field flatness across the entire 44
mm imaging plane. Its oversized lenses ensure a larger and clearer aperture and also extremely
minimized halation.
Quick overview:
120 mm apochromatic, 3-element refractor
840 mm (f/7)
Metallic high-transmission lens coatings
3" CNC machined 1:11 dual-speed focuser
Zero color fringing even on bright objects
44 mm image circle
Knife-edge Baffled Optical System
2" Diagonal with dielectric coatings
9x50 erect-image 90° finder scope
Tube rings with dovetail D (Losmandy style) bar
Aluminum foam lined case
Thread-on field flattener
Full frame corrected focal plane
NEVER USE YOUR TELESCOPE TO LOOK DIRECTLY AT
THE SUN. PERMANENT EYE DAMAGE WILL RESULT.
NEVER USE AN EYEPIECE-TYPE SOLAR FILTER.
NEVER USE YOUR TELESCOPE TO PROJECT SUNLIGHT
ONTO ANOTHER SURFACE; THE INTERNAL HEAT BUILD-
UP WILL DAMAGE THE TELESCOPE OPTICAL ELEMENTS.
USE A PROPER SOLAR FILTER FIRMLY MOUNTED ON THE
FRONT OF THE TELESCOPE FOR VIEWING THE SUN.
WHEN OBSERVING THE SUN, PLACE A DUST CAP OVER
YOUR FINDERSCOPE OR REMOVE IT TO PROTECT YOU
FROM ACCIDENTAL EXPOSURE.
NEVER LET A TELESCOPE POINTING THE SUN
UNATTENDED.

3
Getting started
Parts description
1. Retractable dew cap
2. Tube rings
3. D (Losmandy) dovetail bar
4. 9x50 erect-image 90° finder
scope
5. 3" 1:11 dual-speed focuser
6. 2" dielectric diagonal
7. 2" eyepiece f= 28mm
Unpacking the telescope
Your telescope is inside the sturdy aluminum padded case
*
, designed to securely carry the telescope
and the tube rings. The case contains and protects the telescope and its accessories. Once open you
will find, alongside the telescope with dew cap retracted:
1. The 9x50 erect-image finder scope with tube rings and mount.
2. The 2" (50.8mm) diagonal.
3. The 2-element thread-on field flattener (used for photography only), guarantees excellent field
flatness across the entire 44 mm imaging plane, allowing picturing the sky with large sensors.
4. Field flattener extender tube for DSLR camera, used to place the camera exactly on the
corrected focal plane.
The field flattener extender tube for DSLR may be in one solid piece or two pieces
screwed together, depending on the dealer’s country. Please refer to page 7 for
further information.
5. 2" eyepiece, f= 28mm.
6. Thread-on field flattener adaptor, used to install the field flattener on the focuser's drawtube.
Some parts may be optional, depending on the dealer's country.
Please check with him if any doubt.
*
Sky-Watcher offers this product with the best available quality in accordance with the legislation of the local
market. This can lead to small differences over time and depending on the area of sale in the world. These
differences do not influence the overall quality which is of the high standard guaranteed by Sky-Watcher
worldwide.

4
Preparing the telescope for an observation
A. Upon delivery, and when not used, the
telescope and its accessories are inside the
aluminum padded case (note: the case may
be different from the picture, depending on
your dealer’s country). Unpack the
telescope and assemble it to your mount
using the included D (Losmandy style)
dovetail bar. Please refer to your mount
manual to properly install the telescope.
B. To extend the dew cap unscrew the two
screws on the aluminum ring (1), then
gently pull the dew cap forward (2). When
in position, tighten the two screws to
ensure the dew cap stays in position (3).
C. The 9x50 erect-image finder scope is a
small fixed magnification scope mounted
on the optical tube. When it is correctly
aligned with the telescope, objects can be
quickly located and brought into the field
of telescope (see also "Aligning the finder
scope" chapter, on next page)
To install the finder scope on the telescope
insert the positive dovetail of the finder
scope support inside the negative dovetail
mounted on the focuser, as shown in
picture.
Cooling the telescope
Telescopes require time to cool down to outside air temperature. This may take longer if there is a big
difference between the temperature of the telescope and the outside air. This minimizes heat wave
distortion inside telescope tube (tube currents). Your telescope would require at least 25 minutes
cooling off to outside conditions. Tip: use this time for planning your session and mount accessories.

5
Aligning the finder scope
The 9x50 erect-image finder scope is a small fixed magnification scope mounted on the optical tube.
When it is correctly aligned with the telescope, objects can be quickly located and brought to the
center of the field.
The alignment should be done at first use and over time if the alignment is no more accurate.
Alignment is best done outdoors in day light when it's easier to locate objects
If it is necessary to refocus your finder scope, sight on an object that is
at least 500 meters (or yards) away. Loosen the locking ring by
unscrewing it back towards the bracket. The front lens holder can now
be turned in and out to focus. When focus is reached, lock it in position
with the locking ring
Choose a distant object that is at least 500 meters (or yards) away and
point the main telescope at the object. Adjust the telescope so that the
object is in the center of the view in your eyepiece.
If you are using the star diagonal the image will be left/right
inverted, like images in a mirror.
Having an erected image, the view you have in the finder
scope has the same orientation as the landscape.
Check the finder scope to see if the object, centered in the
main telescope view, is centered on the crosshairs. If not
unscrew the three blocking rings on the rear ring, then adjust
the three small screws to center the finder scope.
Do not over tighten the screws when aligning the finder
scope. When the finder scope is correctly oriented, screw the
three blocking rings in position.

6
Using the telescope for visual observation
Inserting the eyepiece
Loosen the two thumbscrews (1)
on the end of the focuser tube.
Insert the 2" diagonal (2) into the
focus tube and re-tighten the
thumbscrews (1) to hold the
diagonal in place.
Loosen the diagonal's screw (3).
For 2" eyepieces (4a), insert it
into the diagonal and secure it by
re-tightening the thumbscrew (3).
For 1.25" eyepieces first insert
the 2" to 1.25" adapter (4b) into
the diagonal and secure by re-
tightening the screw (3). Loosen
the adapter's screw (5) and insert
the 1.25" eyepiece (6) inside the
adapter ring, then secure it by re-
tightening the screw (5).
Focusing
Make sure the locking lever below the focuser (1) is
unlocked (position as shown in picture).
Slowly turn the focus knobs (2) one way or the other,
until the image in the eyepiece is nearly sharp.
To finely focus the image turn the 1:11 knob one way or
the other until the image is perfectly sharp (3).
Lock the screw below the focuser (1) if a heavy load is
attached (pull the lever at 90°).
The image usually has to be finely refocused over time, due
to small variations caused by temperature changes. This
often happens when the telescope has not yet reached
outside temperature.
Refocusing is almost always necessary when you change an
eyepiece.
When looking through a diagonal, the image
is inverted left to right, as an image in a
mirror. This is normal and has no incidence
for astronomical observations.
If you plan to do terrestrial observation often, like bird
watching, optional image-erecting devices such as the
Amici prism or the erected 90° diagonal may be the right
tool.
Your reseller will be glad to advise you about the best
optional part that can be used with your telescope.

7
Using the telescope for prime focus imaging
Before installing the field flattener onto the drawtube of the
focuser, the 2" ring adaptor (2) needs to be unscrewed and
removed.
In order to easily unscrew the ring, hold with one hand the ring (1)
at the end of the drawtube and then unscrew the 2" ring adaptor
(2) with the other hand.
The Sky-Watcher ESPRIT 120 Field flattener has been specifically designed for your
telescope. It guarantees excellent field flatness across the entire 44 mm imaging plane
and ensures full illumination with extremely minimized halation and zero color fringing
even on bright objects.
No "universal" field flattener available on the market will deliver the premium results
achieved with the Sky-Watcher ESPRIT 120 Field flattener which is designed
exclusively for this telescope.
Installing the field flattener and a DSLR (Digital Single-Lens Reflex) camera
1. Screw the drawtube adaptor (1)
at the end of the focus tube.
2. Screw the field flattener (2)
onto the drawtube adaptor (1).
3. Screw the extender tube (3)
onto the field flattener (2).
If your extender tube has two
parts screwed together
(3a+3b), please check the two
parts are secured tight before
inserting them in the optical
train.
4. Screw the enlarged 48mm T-
Ring (4) onto the extender tube
(3).
5. Install your DSLR camera on
the 48mm enlarged T-Ring (4) –
see note below.
The enlarged 48mm T-Ring may not be included with your telescope and should match
your DSLR camera's manufacturer and model. Please check with your reseller to get the
correct 48mm Enlarged T-Ring for your DSLR camera.

8
In order to get the premium results the field flattener for
ESPRIT 120 can deliver the distance between the last
lenses to the sensor should be exactly 75mm. This
distance is called the field flattener "back focus".
The rings are designed to provide 75mm of back focus
with any DSLR camera. Modifications to this layout, i.e.
by adding a radial guider, will lead to blurry stars images
in the field edges.
Installing a 48mm filter inside the focal extender
A 48mm (2") filter can be mounted inside the DSLR extender tube if needed. By example using a light
pollution reducer filter may allow pictures of the night sky even in suburban areas.
Single part Extender
Inside the focal extender
a 48mm thread receive
any 48mm (2") filter.
Insert the filter and screw
it on the thread. Do not
over tight the filter.
Use a tissue when
screwing the filter to
avoid fingerprints.
2 parts Extender
Please unscrew the two
parts of the Extender.
Insert the filter inside
the 48mm inner thread
of the second part.
Do not over tight the
filter.
Reassemble the 2 parts.
Installing the field flattener and a CCD (Charge-Coupled Device) camera
CCD cameras differ from one model to another, even in the same brand name, by the threads used and
the body-to-sensor distance. Accessories also have different possible threads and depths, thus the
combination of a CCD camera and its accessories can have any total length and any coupling thread.
A custom coupling ring is needed in order to assemble the CCD camera and its accessories (called the
"optical train") to the telescope's field flattener. The custom ring should be machined
†
to have:
1) A female M62x1 thread, to screw and secure the ring to the field flattener exit.
2) A thread compatible with the first component of the optical train.
3) A length to ensure that the distance from the back of the field flattener to the CCD sensor is
exactly 75mm.
The 75mm distance is measured from the edge
marking the start of the male thread on the field
flattener, to the CCD sensor (see picture on the left).
Most CCD cameras have also the distance from their
body thread to CCD sensor noted in the manual, thus
evaluating the length of the custom ring you need
can be precisely evaluated.
†
Refer to your local dealer about custom ring supply.

9
Installing the field flattener and a CCD camera - continued
1. Screw the drawtube adaptor (1) at the
end of the focus tube.
2. Screw the field flattener (2) onto the
drawtube adaptor (1).
3. Screw the custom ring (3) onto the
field flattener (2).
The custom ring needs to be
sturdy enough to secure the
optical train to the field
flattener.
4. Screw your optical train to the custom
ring (3).
Focusing
Make sure the locking lever below the focuser (1) is
unlocked (position as shown in picture).
Slowly turn the focus knobs (2) one way or the other,
until the image in the eyepiece is nearly sharp.
To finely focus the image turn the 1:11 knob one way or
the other until the image is perfectly sharp (3).
Lock the screw below the focuser (1) if a heavy load is
attached (pull the lever at 90°).
The image usually has to be finely refocused over time, due
to small variations caused by temperature changes. This
often happens when the telescope has not yet reached
outside temperature.
Framing the picture
When the object you want to picture is in the middle of the circular 44mm field, most often its
orientation on the rectangular camera sensor is not what you expected (figure A). You can easily
reframe the picture on the camera sensor by unscrewing the blocking ring (1) at the end of the focuser
drawtube, then turning the adapter ring (2) with all the optical train until the framing suits your needs
(figure B). When done screw the ring (1) to lock position, and you are ready to picture the sky.

10
Useful tips for all observations
Removing the finder scope
During an observation, when the desired target is acquired, it
is possible to remove the finder scope from its support. When
needed the finder scope can be inserted again.
This can be useful when the observer's head is in a position
where the finder scope becomes an obstacle to observation.
Using the indexed scale
The indexed scale on the focuser drawtube gives an accurate
indication on the focus position for various accessories.
Once the position for one accessory is known it is very easy to
approximate the focus position.
Due to the precision needed to reach perfect focus a fine
tuning is advised.
Rotating the focuser
The whole focuser body can be rotated. It is useful when the
focuser knobs aren't in a convenient position.
1. Remove all accessories from the focuser.
2. Fully retract the drawtube inside the focuser body.
3. Unscrew the "boat wheel" like large aluminum ring.
4. Rotate the focuser body.
5. Tight back the "boat wheel" like large aluminum ring.

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Specifications
Telescope specifications
Optical Design
Refractor (air-spaced triplet APO)
Field Flattener
Thread-on (2 lenses)
Aperture (mm)
120 mm (4.72 in)
Focal Length
840 mm (33 in)
Focal Ratio
7
Finderscope
9x50, erect-image, right-angle
Diagonal
2" dielectric coatings
Tube Rings
With 3" (D Style) dovetail plate
Highest Useful Magnification
283 x
Lowest Useful Magnification
17 x
Limiting Stellar Magnitude
12.9
Resolution (Rayleigh)
1.16 arc seconds
Resolution (Dawes)
0.97 arc seconds
Light Gathering Power (Compared to Human Eye)
294 x
Optical Coatings
Fully multi-coated
Fully Illuminated Field With Field Flattener
44 mm (1.7 in)
Optical Tube Length (Retracted Dew Cap)
76.2 cm (30 in)
Optical Tube Weight
10 kg (23 lbs)
Telescope Visual Backfocus

>225mm (8.86 in)
Field Flattener Backfocus**
75mm (3 in)
Threads specifications
The 2 parts Extender threads
Full DSLR train with single part Extender or
with two parts Extender screwed together.
Rings/
Threads
Focuser
Tube
Drawtube
Adatpor
Field
Flattener
DSLRl
Ext. Tube
Enlarged
T-Ring
In Ø
n/a
M74x1 F.
M65x1 F.
M62x1 F.
M48x0.75 F.
In screw depth
n/a
7 mm
7.5 mm
8.5 mm
variable
Out Ø
M74 x1 M
M65x1 M.
M62x1 M.
M48x0.75 M
Camera
Out screw depth
6 mm
6 mm
6 mm
6 mm
n/a
The visual back focus of the telescope is the distance from the end of the focuser tube (with 2’’ adapter
installed) to the focal plane. This means, all accessories needing 225mm back focus or less can be installed.
** The back focus of the field flattener is the distance from the back of the field flattener to the focal plane.

12
Different releases: The Helinear Focuser
Some of the first ESPRIT 120 series were delivered with a different focuser: the Helinear focuser.
Focusing with the Helinear focuser
Unlock the locking screw below the focuser (1).
Slowly turn the focus knobs (2) one way or the other,
until the image on the eyepiece or the camera sensor is
nearly sharp.
To finely focus the image turn the 1:11 knob one way or
the other until the image is perfectly sharp (3).
Lock the screw below the focuser (1).
The image usually has to be finely refocused over time, due
to small variations caused by temperature changes.
Before doing prime focus imaging
Before installing the field flattener onto the drawtube of the Helinear
focuser, the 2" ring adaptor (2) needs to be unscrewed and removed.
In order to easily unscrew the ring, the blocking thumbscrew (1) at the
end of the drawtube needs to be tight to lock the rotating end cap.
Framing a picture with the Helinear focuser
When the object you want to picture is in the middle of the circular 44mm field, most often its
orientation on the rectangular camera sensor is not what you expected (figure A). You can easily
reframe the picture on the camera sensor by unlocking the thumbscrew at the end of the focuser
drawtube and turning all the optical train until the framing suits your needs (figure B). When done
relock the thumbscrew, and you are ready to picture the sky.

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We want to ensure that your experience with a Sky-Watcher
product is the best it can be. To make that happen we have a
comprehensive technical and customer support available,
alongside with the list of distributors and dealers worldwide, on
our worldwide internet site:
http://www.skywatcher.com
Sky-Watcher offers this product with the best available quality in
accordance with the legislation of the local market, and reserves the
right to modify or discontinue, without prior notice to you, any model
or style telescope.