Vixen BT81S-A User manual

.
BT81S-A Shown with the Fork Mount,
Tripod and other Optional Accessories available separately
Instruction Manual for BT81S-A Binocular Telescope
WARNING!
SPECIFICATIONS
COMPONENTS
BT81S-A Shown with the Fork Mount,
Tripod and other Optional Accessories available separately
Never look directly at the sun with your naked eyes or through this product or its finder scope available.
Permanent and irreversible eye damage may result.
Thank you for your purchase of a Vixen BT81S-A Binocular Telescope. This manual applies to the BT81S-A Binocular Telescope.
Be sure to read instructions for the mount and tripod along with this manual if you purchased the product as a complete package
*For observing, two 31.7mm (1.25-inch) eyepieces of the same focal length are required as they are not included.
*A pair of the eyepieces are included if you purchase a complete package consisting of the BT81S-A, HF2 Altazimuth Fork Mount ans SXG-HAL130 tripod.
Do not leave the product uncapped in daytime. It may cause passing sunlight through
the objective lens of the optical tube, resulting in fire
Do not use the product while transporting or walking, as injuries may arise from
stumbling, falling or collision with objects.
Keep plastic and vinyl packing materials away from children; these may cause danger
from swallowing or suffocation.
The specifications are subject to change without notice.
About eyepieces applicable to BT81S-A
The detachable eyepieces can be swapped for other Vixen SLV or LVW or SSW series
of 31.7mm-size eyepieces, but if the eyepieces with high magnification are used, it
may give rise to misalignment that is become detectable due to its high magnification.
It is always recommendable to use the eyepieces with focal length longer than 10mm
for observing to avoid it.
Do not leave the product inside a car in bright sunshine, or in hot places. Keep any
strong heat radiation sources away from the product.
Do not exposure the product to rain, water drops, dirt or sand.
When cleaning, do not use solvent such as paint thinners.
Avoid touching any lens surfaces directly with fingers. If a lens becomes dirty with
fingerprints or general smears, gently wipe it using a commercially available lens leaner
and a lens cleaning paper, or consult your local Vixen dealer.
For storage, keep the product in dry places, and do not expose to direct sunlight.
CAUTION HANDLING • STORAGE
Objective lens Air-spaced doublet achromatic
Optical coating Magnesium fluoride coating
Effective aperture 81mm
Focal length (Focal ratio) 480mm (F/5.9)
Resolving power 1.43 arc seconds
Limiting magnitude 11.3
Light gathering power 134x
Eyepiece holders Friction fit type
Eyepieces applicable
(Optional)
SLV series of 31.7mm size or LVW series of
31.7mm size or SSW series of 31.7mm size
Interpupillary distance 58mm to 102mm
Optional Accessories 7x50mm finder scope & bracket or X-Y red
dot finder
Mount block / Threads Dovetail bar for SX/GP
Threaded sockets 1/4-inch x 2 & 3/8-inch x 1
Size & weight 480mm L x 190mm W x 155mm H, 4.1kg (9 lbs)
Carry Handle
Objective Cap
BT81S-A
Threaded sockets
for camera tripods
7x50 Finder Scope
(Optional)
XY Finder bracket
(Optional)
Eyepieces
(Optional)
Swing Bracket
(Optional)
SXG-HAL130 Tripod (Optional)
HF2 Fork mount
(Optional)
Eyepiece Holders
Friction Fit
Focus Ring
Prism Housing
45-degree Angle
Finder-bracket Shoe
Dovetail Bar
Optical Tube
Dew Shield
Objective Lens
(inside)

1
1 2
3 4
2
USING YOUR BT81S-A BINOCULAR TELESCOPE
ALIGNMENT
1
The BT81S-A has threaded sockets of 1/4”-20 and a 3/8” on the bottom
of the dovetail bar that fit directly to a camera tripod. 2
Attach the eyepieces so that the chrome barrel of the eyepiece is push
into the eyepiece holder and fixed by friction. When you exchange the
eyepieces, you should align the optical axis of left side and right side
eyepieces in the procedure stated in ALIGNMENT.
3
While looking through the right side eyepiece, turn the focus ring on the
right side prism housing until the image appears in sharp focus. Next,
look through the left side eyepiece and adjust the focus of the left side
eyepiece in the same way by turning the left side focus ring.
1
Look through the left side eyepiece and find an object further than
1,000m distant. Put the object in the field of view so that it lies on the
imaginary horizontal center line of the field of view, and shift it to the very
right edge. An electric pole is shown here as a sample.
The object near the edge of the field of view makes your recognition of a
position of the object against the field of view circle easier.
If the object is seen at the same level and position on the right side
eyepiece as seen with the left side eyepiece, it shows that the eyepieces
are aligned correctly.
If not, rotate the right side eyepiece slowly clockwise or
counterclockwise until the object moves toward the same position.
2If the above does not align the optics correctly, then rotate the left side eyepiece slowly while keeping the right side eyepiece as it is.
It may be possible that a double vision occurs from the character of binoculars when you attach the eyepieces without a consideration for
optical alignment. In this case, make adjustments of the optical axis in the following procedure.
The object can be seen more clear and brighter at low magnification. It is desirable to start with a pair of eyepieces with low magnification and
exchange them for eyepieces with medium magnification. It will be hard to align the optical axis at high magnification due to the structure of binocular
telescopes. (It is advisable to use with the Vixen SLV or LVW eyepieces with focal length longer than 10mm at high magnification.)
TIPS ON GENERAL OBSERVATION WITH BT81S-A
How to Adjust a Double Vision
4
Adjust the interpupillary width to your eyes. Hold the left and right side
prism housings with both hands and rotate them inward equally so that
the both eyepieces come to a position that fits your eyes. It is a point
that circles of field of view in the left and right eyepieces become one
completely.
Dovetail barDovetail bar
EyepiecesEyepieces
(Optional)(Optional)
Left sideLeft side
prism housingprism housing
Right sideRight side
prism housingprism housing
ChromeChrome
barrelbarrel
Eyepiece holderEyepiece holder
Camera tripodCamera tripod
Left side focus ringLeft side focus ring
Right side focus ringRight side focus ring
1/4“ -201/4“ -20
3/8“3/8“
Imaginary horizontal line
Left
Left
Right
Right
Shift the object to the very right edge
VIXEN - European Distributor Bresser GmbH Gutenbergstrasse 2, D-46414 Rhede, Germany
Phone: [phone] – 80 740 E-Mail: [e-mail] www.bresser.de