National Geographic NT114CF User manual

11
SUN HAZARD — Never look directly at the sun
with this device.
WARNING:
CHOKING HAZARD — Small parts.
Not for children under 3 years.
WARNING:
Contains button or coin cell battery.
Hazardous if swallowed — see instructions.
WARNING:
INCLUDED
X 1
The lens contains lead that may be harmful.
Wash hands after touching.
WARNING:
This product can expose you to chemicals including lead,
which is known to the State of California to cause cancer.
For more information go to www.P65Warnings.ca.gov.
WARNING:
80-30114
US
10 +
NT114CF
114 MM NEWTONIAN REFLECTOR
W/ PANHANDLE MOUNT
INSTRUCTION MANUAL

2
Customer Service: Call 1-866-252-3811
• SUN WARNING: WARNING: NEVER ATTEMPT TO OBSERVE THE SUN WITH THIS DEVICE! OBSERVING THE
SUN  EVEN FOR A MOMENT  WILL CAUSE INSTANT AND IRREVERSIBLE DAMAGE TO YOUR EYE OR EVEN
BLINDNESS. EYE DAMAGE IS OFTEN PAINLESS, SO THERE IS NO WARNING TO THE OBSERVER THAT THE
DAMAGE HAS OCCURRED UNTIL IT IS TOO LATE. DO NOT POINT THE DEVICE AT OR NEAR THE SUN. DO NOT
LOOK THROUGH THE DEVICE AS IT IS MOVING. CHILDREN SHOULD ALWAYS HAVE ADULT SUPERVISION WHILE
OBSERVING.
• RESPECT PRIVACY: WHEN USING THIS DEVICE, RESPECT THE PRIVACY OF OTHER PEOPLE. FOR EXAMPLE, DO NOT
USE IT TO LOOK INTO PEOPLE’S HOMES.
• CHOKING HAZARD: CHILDREN SHOULD ONLY USE DEVICE UNDER ADULT SUPERVISION. KEEP PACKAGING
MATERIALS LIKE PLASTIC BAGS AND RUBBER BANDS OUT OF THE REACH OF CHILDREN AS THESE
MATERIALS POSE A CHOKING HAZARD.
• RISK OF BLINDNESS: NEVER USE THIS DEVICE TO LOOK DIRECTLY AT THE SUN OR IN THE DIRECT PROXIMITY OF THE
SUN. DOING SO MAY RESULT IN A PERMANENT LOSS OF VISION.
• RISK OF FIRE: DO NOT PLACE DEVICE, PARTICULARLY THE LENSES, IN DIRECT SUNLIGHT. THE CONCENTRATION OF
LIGHT RAYS COULD CAUSE A FIRE.
• DO NOT DISASSEMBLE THIS DEVICE: IN THE EVENT OF A DEFECT, PLEASE CONTACT YOUR DEALER. THE DEALER
WILL CONTACT THE CUSTOMER SERVICE DEPARTMENT AND CAN SEND THE DEVICE IN TO BE REPAIRED IF
NECESSARY.
• DO NOT SUBJECT THE DEVICE TO TEMPERATURES EXCEEDING 60 °C 140 °F.
• DISPOSAL: KEEP PACKAGING MATERIALS, LIKE PLASTIC BAGS AND RUBBER BANDS, AWAY FROM
CHILDREN AS THEY POSE A RISK OF SUFFOCATION. DISPOSE OF PACKAGING MATERIALS AS LEGALLY
REQUIRED. CONSULT THE LOCAL AUTHORITY ON THE MATTER IF NECESSARY AND RECYCLE MATERIALS
WHEN POSSIBLE.
• THE WEEE SYMBOL IF PRESENT INDICATES THAT THIS ITEM CONTAINS ELECTRICAL OR ELECTRONIC
COMPONENTS WHICH MUST BE COLLECTED AND DISPOSED OF SEPARATELY.
• NEVER DISPOSE OF ELECTRICAL OR ELECTRONIC WASTE IN GENERAL MUNICIPAL WASTE. COLLECT AND
DISPOSE OF SUCH WASTE SEPARATELY.
• MAKE USE OF THE RETURN AND COLLECTION SYSTEMS AVAILABLE TO YOU, OR YOUR LOCAL RECYCLING PROGRAM.
CONTACT YOUR LOCAL AUTHORITY OR PLACE OF PURCHASE TO FIND OUT WHAT SCHEMES ARE AVAILABLE.
• ELECTRICAL AND ELECTRONIC EQUIPMENT CONTAINS HAZARDOUS SUBSTANCES WHICH, WHEN DISPOSED OF
INCORRECTLY, MAY LEAK INTO THE GROUND. THIS CAN CONTRIBUTE TO SOIL AND WATER POLLUTION WHICH IS
HAZARDOUS TO HUMAN HEALTH, AND ENDANGER WILDLIFE.
• IT IS ESSENTIAL THAT CONSUMERS LOOK TO REUSE OR RECYCLE ELECTRICAL OR ELECTRONIC WASTE TO AVOID IT
GOING TO LANDFILL SITES OR INCINERATION WITHOUT TREATMENT.
BUTTON/COIN BATTERY WARNING: THIS PRODUCT CONTAINS A BUTTON OR COIN CELL BATTERY. A SWALLOWED
BUTTON OR COIN CELL BATTERY CAN CAUSE INTERNAL CHEMICAL BURNS IN AS LITTLE AS TWO HOURS AND LEAD
TO DEATH. DISPOSE OF USED BATTERIES IMMEDIATELY. KEEP NEW AND USED BATTERIES AWAY FROM CHILDREN. IF
YOU THINK BATTERIES MIGHT HAVE BEEN SWALLOWED OR PLACED INSIDE ANY PART OF THE BODY, SEEK IMMEDIATE
MEDICAL ATTENTION.
IMPORTANT SAFETY INSTRUCTIONS
READ AND FOLLOW THE INSTRUCTIONS BEFORE USE.
KEEP THESE INSTRUCTIONS FOR LATER USE.

3
6
7
1
9
11 12
13
8
Parts Overview
1. 114mm Telescope
2. Panhandle Alt-Azimuth Mount
3. Tripod
4. Accessory Tray
5. Focus Wheel/Focuser
6. 1.25” Eyepieces (9.7mm and 26mm)
7. 2x Barlow Lens
8. Red Dot Viewfinder
9. Smartphone Adapter
10. Leg Locking Knob
11. Telescope Mount Bracket
12. Mount Locking Knob
13. Eyepiece Locking Screws
14. Azimuth (horizontal) Tension Knob
15. Red Dot Adjustment Screws
3
10
15
15
4
2
14
5
*phone not included
What’s Included:
Available Downloads Visit:
www.exploreone.com/pages/product-manuals

4
6a)
5a)
5b)
6b)
8)
11)
9a) 9b) 9c)
7a)
10a)
=
10b) 10c)
10d)
10e)
7b)
1) 2) 3a) 4)
2019
26mm
1
2
3b2)3b1)
1
2
How To Set Up
Note: We recommend assembling your telescope for the first time in the daylight or in a lit room so that you can
familiarize yourself with assembly steps and all components.

5
Using/Aligning the Red Dot Viewfinder:
The viewfinder is powered by a CR-1620 battery that is
included. Before using the viewfinder for the first time,
remember to remove the plastic insulator that is blocking
the battery from connecting.
Note: Please recycle used batteries responsibly.
For The Viewfinder To Be Effective,
It Must Be Aligned
Insert the 26 mm eyepiece into the focuser and power on the
viewfinder by flipping the switch to the “On” position.
10a. Point the telescope at an easy to identify target like a
tree that is approximately 200 yards away. Center the object
in the eyepiece. Lock the telescope into place by tightening
the panhandle.
Note: Terrestrial objects may appear inverted, sideways
or at an angle depending on how your tube is oriented
due to optical design. This rotation is perfectly normal on
all Newtonian reflectors and will not affect astronomical
viewing.
10b-e. Without moving the telescope, position the red dot using the two adjustment screws(Part 15) so that it shares
the same view as the one in your eyepiece.
Note: To preserve battery life, don’t forget to turn off the viewfinder after use.
11. Telescope is ready for viewing.
How To Set Up
Note: We recommend assembling your telescope for the first time in the daylight or in a lit room so that you can
familiarize yourself with assembly steps and all components.
1. Take the tripod (Part 3) and fully extend each leg.
2. Align the accessory tray (Part 4) and turn 180 degrees to lock into place.
3a. Assemble the panhandle mount (Part 2) by screwing in the handle and placing the mount onto the tripod.
3b1. If the mount includes a locking knob, insert the washer first then the spacer and turn the knob to securely lock the
mount to the tripod.
3b2. If the mount includes a locking screw, insert the washer first then the spacer and using a hex wrench (if included),
turn the screw to securely lock the mount to the tripod.
4. Adjust the height of the tripod by unlocking the leg locking knob first (Part 10) and slide one tripod leg at a time to
the preferred length. Repeat this two more times.
5a. Grab your 114mm telescope (Part 1) and locate the red dot viewfinder mount bracket at the front of telescope.
5b. Slide in the red dot viewfinder (Part 8) by aligning the two hollow circles on the red dot viewfinder to the mount
bracket.
6a-b. Locate the mounting bracket at the bottom of your telescope (Part 11). Slide in the telescope and lock it into place
with the mount locking screw (Part 12).
7a. Remove the dust cover from the telescope and insert an eyepiece. 26 mm is preferred.
7b. Tighten the eyepiece locking screws (Part 13) on the focuser (Part 5) to secure the eyepiece in place.
8. To move the telescope up or down, loosen the handle (Part 2), move the telescope up or down and tighten the handle
to lock it to the desired position.
9a. To turn the telescope left or right, loosen the azimuth (horizontal) tension knob. (Part 14).
9b. Turn the telescope left or right to the desired position.
9c. Tighten the azimuth (horizontal) tension knob (Part 14) to keep the telescope securely in place.
CR1620
BATTERY
3V
The Red Dot Viewfinder is
powered by a battery type CR-1620
(3V); if a replacement is necessary,
remove cap (Fig. 1) by twisting
counter clockwise (Fig. 2) remove old
battery and insert new battery in place
with the positive (+) side showing.
Replace cap and tighten clockwise.
Please recycle batteries responsibly.
Fig. 1 Fig. 2
Red Dot Viewfinder
(back view)
English

6
Using Your Telescope:
After you have aligned your viewfinder, you are ready to start observing! Put the 26mm eyepiece into the focuser to get
the widest field of view. This wider field of view will make it easier to locate and track objects. Use the panhandle to
move the scope up, down and side to side until your target comes into view in the eyepiece. It is important to remember
that the rotation of the Earth means objects will move out of your eyepiece fairly quickly. Once you have found and
focused on your desired target, you can track it as it journeys across the night sky using the panhandle.
To get a closer look at an object, take out the 26mm eyepiece and replace it with the 9.7mm eyepiece. This will increase
the magnification to 51.5x. For the strongest magnification, take out the 9.7mm eyepiece and insert the 2x Barlow lens
into the focuser. Put the 9.7mm eyepiece into the Barlow lens and secure it in place, this will up the magnification from
51.5x to 103x. If you use the Barlow lens with the 26 mm eyepiece, the magnification will change from 19x to 38x.
Note: This telescope is designed for astronomical
use. Terrestrial objects may appear inverted,
sideways or at an angle depending on how your
tube is oriented due to optical design. This
rotation is perfectly normal on all Newtonian
reflectors and will not affect astronomical
viewing.
Cleaning:
The internal optics of your reflector telescope will rarely requiring cleaning as long as you put the dust cover on when
the device is not in use. Small particles of dust that may enter the optical tube assembly during an observing session
should not impact image quality. In the rare circumstance that a film of dirt collects on either mirror, you will need to
contact Customer Service at [phone] or service@explorescientific.com to arrange for the device to be returned to
our facility for disassembly, cleaning and collimation. Although the optics inside of the reflector will likely never require
cleaning as long as the dust cover is on when the telescope is not in use, eyepieces will need to be kept free of dust and
dirt. To clean the eyepiece, use only a photo-grade soft brush or a lint-free cloth to gently remove any particles from the
lens. Do not press down hard while cleaning as this might scratch the lens. If the eyepiece lens is exceptionally dirty, it
may be necessary to dampen a lint-free cleaning cloth with an optical glass cleaning fluid and then wipe the lens clean
using very light pressure. The eyepiece is NOT waterproof so do not spray fluids directly onto the glass or dip it in
water. Never use harsh detergents! After you have finished cleaning an eyepiece, allow it to fully dry before storing.
Troubleshooting Guide:
Problem Solution
No picture Remove dust protection cap.
Blurred picture Adjust focus using focus wheel.
No focus possible Wait for temperature to balance out.
Bad quality Never observe through a glass surface such as a window.
Viewing object visible in the finder, but
not through the telescope Align finder to telescope (see instructions)
Focal Length Eyepiece Magnification 2x Barlow Lens
500mm 26mm 19x 38x
500mm 9.7mm 51.5x 103x

7
Using The Smartphone Adapter:
SUPERVISION BY ADULTS
Read and follow the instructions, safety rules and first aid information
The Smartphone Adapter will allow you to connect almost any “smart” device to a 1.25” eyepiece.
To use the adapter, place it directly onto the selected eyepiece and secure it by tightening the set screw until snug.
Be careful not to overtighten because this could damage the adapter and/or the eyepiece.
The camera lens on your smart device will need to be centered over the eyepiece. This alignment is best done by
opening the camera function and viewing the image while you center the device. Once you have positioned the device
correctly, carefully press it onto the suction cup/non-skid surface of the adapter pad. Never allow the adapter pad to
hold your device without you supporting the item as well.
The point at which you secure the eyepiece/adapter combination into the diagonal/focuser depends largely on the
dimensions of your device. For smaller devices like smart phones, it may be easier to secure it to the eyepiece/adapter
combination before inserting the entire unit into the diagonal on the telescope. For larger devices, such as tablets, it
may be easier to secure the eyepiece/adapter combination into the diagonal, and then align and attach your device.
After positioning your device and capturing images, you can enhance and edit the photos using the imaging software of
your choice. One option can be found at https://www.getpaint.net/.
WARNING: Do not leave your device unsupported or unattended on the adapter pad.
Though the surface of the adapter pad is designed with suction cups and is non-skid, the manufacturer cannot assure
that the pad will support the weight of various devices or guarantee that it will adhere to all surfaces on various smart
devices. The pad is not intended to secure, balance or support the device on its own, and the operator should not let
the device rest solely on the adapter pad. Leaving the device unattended or allowing it to balance on its own without
operator support may result in the device falling, unbalancing the entire instrument and possibly damaging the
telescope or your smart device.
CHEMICALS
Any chemicals and liquids used in preparing, using, or cleaning should be kept out of reach of children. Do not drink
any chemicals. Hands should be washed thoroughly under running water after use. In case of accidental contact
with the eyes or mouth rinse with water. Seek medical treatment for ailments arising from contact with the chemical
substances and take the chemicals with you to the doctor.
Keep packaging materials (plastic bags, rubber bands, etc.) away from children. There is a risk of SUFFOCATION.
Dispose of packaging materials as legally required. Consult the local authority on the matter if necessary.
DISPOSAL
Dispose of the packaging materials properly, according to their type, such as paper or cardboard. Contact your local
waste-disposal service or environmental authority for information on the proper disposal. Please take the current legal
regulations into account when disposing of your device. You can get more information on the proper disposal from your
local waste-disposal service or environmental authority.

8
Observing Tips:
Star hopping
Star hopping is a technique used by amateur astronomers to navigate the night sky. By using easily recognizable
constellations and asterisms as a guide, an observer can locate stars and other objects.
For example, Polaris, which is
commonly referred to as The North
Star, can be located quickly using
star hopping. First, find the Big
Dipper asterism in the Ursa Major
constellation. The popular pattern is
defined by seven stars, and the two
stars on the front edge of the Big
Dipper’s “bowl” are Merak and Dubhe.
Next, draw an imaginary line from the
bottom star (Merak) on this front edge
through the top star (Dubhe) on the
front edge. Follow the line to the first
bright star you see. That should be
Polaris. Finally, to verify your finding,
locate the Little Dipper asterism.
Polaris is the anchor star at the end of
the Little Dipper’s “handle.”
BIG DIPPER
LITTLE DIPPER
POLAR STAR
CASSIOPEIA
Caph
Zeta Beta
Kochab
Pherkad
Gamma
Eta
Epsilon
Delta
Alpha
Shedar
Cih
Ksora
Segin
Alkaid
Alcor Mizar
Alioth
Megrez
Phecda
Merak
Dubhe
Orion Nebula(M42):
Right ascension: 05: 35.4 (hours: minutes)
Declination: -05: 27 (degrees: minutes)
Distance: Approximately 1,344 light years
The Orion Nebula is a vast star-forming region located in the “sword”
branching off of the famous Orion’s Belt. Also known as Messier 42,
this diffuse nebula is bright enough to see with the unaided eye —
although it will only appear as a slightly foggy star. However, with
your telescope, you can see many of the beautiful details, such as the
billowing clouds of gas and dust where new stars are being born.
Image credit: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA)
and the Hubble Space Telescope Orion Treasury Project Team
Image credit: Howard Eskildsen
Note: Images are for illustration purposes only. Quality of your image may very depending upon atmospheric conditions and location.
Possible Objects for Observation:
What you can observe at any one time in your telescope depends on
several factors beyond aperture and magnification. These factors include
location, date, time and sky conditions. The following are all objects that
can be seen with the unaided eye and/or binoculars. Your telescope can
enhance views of any of these objects if the observing conditions are right.
The Moon:
Diameter: 3,476 km
Distance: Approximately 384,401 km
The Moon is the Earth’s only natural satellite, and it is the second
brightest object in the sky (after the Sun). Although it is our closest
neighbor, a lot of people have never really taken a good long like at the
Moon. With your telescope, you should be able to see several interesting
lunar features. These include lunar maria, which appear as vast plains,
and some of the larger craters. The best views will be found along the
terminator, which is the edge where the visible and shadowed portions of
the Moon meet.
Note: The positioning of the Big Dipper in relation to the Little Dipper does not
change, but the orientation of both in the night sky will rotate throughout the
year due to the motion of the Earth.

99
Pleiades Star Cluster(M45):
Right ascension: 03: 47.0 (hours: minutes)
Declination: +24: 07 (degrees: minutes)
Distance: Approximately 444 light years
The Pleiades Star Cluster is a group of brilliant blue stars
located in the Taurus Constellation. Also known as Messier
45 or “Seven Sisters”, this open star cluster consists of more
than 1,000 confirmed stars, although an average of only six
are visible to the unaided eye. With your telescope, you can
quickly reveal some of the more elusive members of this
legendary and beautiful cluster.
Dumbbell Nebula(M27)
Right ascension: 19:59.6 (hours: minutes)
Declination: +22:43 (degrees: minutes)
Distance: Approximately 1,360 light years
The Dumbbell Nebula was the first planetary nebula ever
discovered. It is one of the most popular sights in the
Vulpecula constellation. Easy to find with binoculars and
amazing in a telescope, the shape of this bright, double-lobed
nebula has been compared to a dumbbell, an hourglass or
an apple core. As an added bonus, the white dwarf that lies
at the heart of the Dumbbell Nebula is larger than any other
star of its kind.
Andromeda Galaxy(M31):
Right ascension: 00: 42.7 (hours: minutes)
Declination: +41: 16 (degrees: minutes)
Distance: Approximately 2.54 million light years
The Andromeda Galaxy is the closest major galaxy to our
own Milky Way. Also known as Messier 31, this famous spiral
galaxy is part of the Local Group of galaxies. Although it is
technically bright enough to see with the unaided eye under
a very dark sky, your telescope may show its bright center,
hints of its spiral structure and its much smaller companion
galaxies known as M32 and M110.
Image credit: NASA/JPL-Caltech/UCLA
Image credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA
Image credit: NASA/JPL-Caltech
Note: Images are for illustration purposes only. Quality of your image may very depending upon atmospheric conditions and location.

1010
Light
Light
Secondary Mirror
Primary Mirror
(Objective)
Focuser
Focuser
Light
Light
Objective Lens
Light
Light
Secondary Mirror
Primary Mirror (Objective)
Correcting Lens
Reflector
(Newtonian)
Refractor
Catadioptric
(Maksutov-Cassegrain/
Schmidt-Cassegrain)
Light
Light
Secondary Mirror
Primary Mirror
(Objective)
Focuser
Focuser
Light
Light
Objective Lens
Light
Light
Secondary Mirror
Primary Mirror (Objective)
Correcting Lens
Reflector
(Newtonian)
Refractor
Catadioptric
(Maksutov-Cassegrain/
Schmidt-Cassegrain)
Light
Light
Secondary Mirror
Primary Mirror
(Objective)
Focuser
Focuser
Light
Light
Objective Lens
Light
Light
Secondary Mirror
Primary Mirror (Objective)
Correcting Lens
Reflector
(Newtonian)
Refractor
Catadioptric
(Maksutov-Cassegrain/
Schmidt-Cassegrain)
Reflector
A reflector telescope uses mirrors to gather and focus light. Light enters the telescope through its open front end and
travels to the concave primary mirror at the back. From there the light is reflected back up the tube to a flat secondary
mirror, which sits at a 45° angle in relation to the eyepiece. Light bounces off of this secondary mirror and out through
the eyepiece. A reflector telescope is designed for astronomical use. Terrestrial objects may appear inverted, sideways
or at an angle depending on how your tube is oriented due to optical design. This rotation is perfectly normal on all
Newtonian reflectors and will not affect astronomical viewing.
Refractor:
A refracting telescope uses a collection of lenses to gather and focus light. A refractor’s views will be upside down if
a diagonal is not in use. A standard diagonal will generate a “right side up” image, however, it will rotate the image on
the vertical axis (mirror image). To get the “right side up” image without the rotation, you will need to use a special
diagonal with an erect image prism.
Catadioptric:
A catadioptric telescope uses a combination of mirrors and lenses to gather and focus light. Popular catadioptric
designs include the Maksutov-Cassegrain and Schmidt-Cassegrain.
Types Of Telescopes:

1111
Aperture:
This figure, which is usually expressed in millimeters, is the diameter of a telescope’s light-gathering surface (objective
lens in a refractor or primary mirror in a reflector). Aperture is the key factor in determining the brightness and
sharpness of the image.
Objective Lens:
The objective lens is the main light-gathering component of a refractor telescope. It is actually composed of several
lens elements.
Diagonal:
This accessory houses a mirror that deflects the ray of light 90 degrees. With a horizontal telescope tube, this device
deflects the light upwards so that you can comfortably observe by looking downwards into the eyepiece. The image in a
standard diagonal mirror appears upright, but rotated around its vertical axis (mirror image). To get an image without
this rotation, you will need to use a special diagonal with an erect image prism.
Eyepiece:
An eyepiece is an optical accessory comprised of several lens elements. It determines the magnification of a particular
observing setup.
Primary Mirror:
The primary mirror is the principle light-gathering surface of a reflector telescope.
Secondary Mirror:
A secondary mirror is a small mirror that sits at a 45° angle in relation to the primary mirror of a reflecting telescope.
Light from the primary mirror is reflected back up the tube to the secondary mirror. The light is directed from this
mirror up into the eyepiece.
Objective Lens
Aperture
(mm)
Aperture
(mm)
Eyepiece
Diagonal Focal Point
Focal Point
Focal Length Telescope
(mm)
Focal Length Telescope
(mm)
Focal Length
Eyepiece
(mm)
Focal Length
Eyepiece
(mm)
Focuser
Secondary
Mirror
Primary Mirror
(Objective)
Focuser
Eyepiece
Telescope Terms to Know:

1212
Magnification:
The magnification corresponds to the difference between observation with the naked eye and observation through
a magnifying device like a telescope. If a telescope configuration has a magnification of 30x, then an object viewed
through the telescope will appear 30 times larger than it would with the naked eye. To calculate the magnification of
your telescope setup, divide the focal length of the telescope tube by the focal length of the eyepiece. For example, a
20mm eyepiece in a telescope with a 1000mm focal length will result in 50x power, which will make the object appear
50 times larger. If you change the eyepiece, the power goes up or down accordingly.
Focal ratio
The focal ratio of a telescope is determined by dividing the telescope’s focal length by its aperture (usually expressed
in millimeters). It plays a key role in determining a telescope’s field of view and significantly impacts imaging time in
astrophotography. For example, a telescope with a focal length of 1000mm and a 100mm clear aperture has a focal
ratio of f/10.
Focal length (Telescope):
The focal length is the distance in millimeters between the objective lens or primary mirror and the point at which
entering light rays converge — otherwise known as the focal point. The focal lengths of the telescope tube and the
eyepiece are used to determine magnification.
Focal length (Eyepiece):
The focal length is the distance in millimeters between the center of the first lens element in an eyepiece and the focal
point. The focal lengths of the telescope tube and the eyepiece are used to determine magnification. Short eyepiece
focal lengths produce higher magnifications than long eyepiece focal lengths.
Exit Pupil
The exit pupil is the diameter of the beam of light coming out of the eyepiece. To calculate exit pupil, divide the focal
length of your eyepiece by your telescope’s focal ratio. For example, if you use a 20mm eyepiece with an f/5 telescope,
the exit pupil would be 4mm.
Magnification = Telescope Focal Length
Eyepiece Focal Length
Focal Ratio = Telescope Focal Length
Telescope Aperture
Exit Pupil = Eyepiece Focal Length
Telescope Focal Ratio
Eyepiece Lens
Long Eye Relief Distance
Eyepiece Lens
Short Eye Relief Distance
Eyepiece Lens
Exit Pupil (mm)
Telescope Focal Length
1000mm
Eyepiece
Focal Length
20mm
Aperture
102mm

13
Eyepiece Lens
Long Eye Relief Distance
Eyepiece Lens
Short Eye Relief Distance
Eyepiece Lens
Exit Pupil (mm)
Eyepiece Lens
Long Eye Relief Distance
Eyepiece Lens
Short Eye Relief Distance
Eyepiece Lens
Exit Pupil (mm)
Eye Relief
Eye relief is all about a comfortable viewing experience because it is the distance at which you need to position your
eye from the eyepiece’s outermost surface to enjoy the full field of view. This characteristic is of special concern to
observers who wear glasses to correct an astigmatism, because a long enough eye relief is necessary to allow room
for glasses.
Huygenian Eyepieces:
A Huygenian eyepiece uses two plano-convex lenses separated by an air gap. They have a fairly narrow apparent field
of view.
Kellner Eyepieces:
A Kellner eyepiece uses three lens elements - two of which are paired together in an achromatic doublet design to
minimize chromatic aberrations. They typically produce an apparent field of view around 45°.
Plössl Eyepieces:
A Plossl eyepiece uses two doublets (a pairing of lens) for a total of four lens elements. This eyepiece design delivers
sharp views and an apparent field of view of approximately 50°, which works well for both planetary and deep sky
viewing.
Barlow Lens:
A Barlow lens effectively increases the focal length of a telescope. It is inserted between the eyepiece and the focuser/
diagonal (depending on the optical setup) and multiplies the magnification power of the eyepiece.
For example, a 2x Barlow will double the magnification of a particular eyepiece.
Barlow Lens
2 Lens Elements
Huygenian Eyepiece
2 Lens Elements
Light
Kellner Eyepiece
3 Lens Elements
Light
Plössl Eyepiece
4 Lens Elements
Light
Light
Eye Lens
Field Lens
Eye Lens
Field Lens
Field Lens

14
Notes:

15
Notes:

1616
©2019 National Geographic Partners LLC. All rights reserved.
NATIONAL GEOGRAPHIC and Yellow Border Design are trademarks of the
National Geographic Society, used under license.
©2019 Explore Scientific, LLC.
1010 S. 48th Street, Springdale AR 72762
All rights reserved. explorescientificusa.com | exploreone.com | 866.252.3811
Made in China
CONTENTS AND COLORS MAY VARY
CONFORMS TO THE SAFETY REQUIREMENTS OF ASTM F963
V042019