6
There are three 1.5” fans built into the rear end of the Levenhuk Ra 250RC F8 OTA. These will reduce the time
it takes the primary mirror to adapt to the outside temperature. The fans are powered by 8 AA batteries (not
included in the kit), or an external 12V battery. Please allow additional time for cooling if there is a substantial
difference between the indoor and outside temperatures. Once the telescope has adapted to the outside tem
-
perature, you can turn off the cooling fans to reduce vibration of the optical tube.
Cooling fans
Eyepiece assembly
7
An eyepiece magnifies the image produced by the OTA. The eyepiece may be installed either into the focuser
directly or into a star diagonal. Eyepieces are commonly referred to by their focal length and barrel diameter.
The focal length of each eyepiece is printed on the eyepiece shell. The longer the focal length, the lower the
eyepiece magnification, and vice versa. The total power of the telescope setup may be calculated with the fol
-
lowing formula:
Magnification = Focal Length of Telescope (mm) / Focal Length of Eyepiece (mm)
To install an optional eyepiece:
1. Loosen the screw on the star diagonal or the focuser;
2. Slide the eyepiece into the star diagonal or the focuser;
3. Retighten the screw to secure the eyepiece in place.
Image orientation
Focusing
The image orientation changes depending on the eyepiece assembly. When using the star diagonal, the image is
upright but mirrored left to right. If inserting the eyepiece directly into the focuser without the star diagonal,
the image will be inverted and mirrored left to right.
One of the exciting new features of Levenhuk optical tubes is the inclusion of the new dual-speed Crayford
focuser. Unlike the traditional Crayford focuser with a spring-loaded shaft to hold the focus tube, the new linear
ball bearing focuser allows you to easily use heavier accessories, such as larger eyepieces, cameras, imagers,
guiders, etc. It also reduces image shake and completely eliminates backlash.
During celestial observations, out-of-focus images of dim stars may be very diffuse, making it difficult to focus
on such objects. Choose a brighter celestial body (such as the Moon) as your first observation object, and focus
your view. With a 10:1 fine focus adjustment (meaning that 10 turns of the fine focus knob equal 1 turn of the
coarse focus knob), you can adjust the focus of your view with great precision. Use the coarse focus knob to
adjust the view until your object is as close to focus as possible, and then make fine adjustments with the fine
focus knob.
Specifications
Model
Levenhuk Ra
200RC F8 Carbon OTA
Levenhuk Ra
250RC F8 OTA
Optical design
Ritchey-Chrétien
Ritchey-Chrétien
Optical tube material
carbon fiber
steel
Mirror shape
hyperboloid
hyperboloid
Mirror material
BK-7
quartz
Mirror сoating
dielectric
dielectric
Focuser
2” dual-speed Crayford
3” dual-speed Crayford
Primary mirror diameter (aperture), mm
200
250
Focal length, mm
1600
2000
Focal ratio
f/8
f/8
Secondary mirror minor axis, mm
90
105
Tube-mount assembly system
dovetail plate
dovetail plate
Optical tube length, in / mm
18.7 / 476
29 / 736
Optical tube diameter, in / mm
9 / 230
11.8 / 299
Tube weight, lbs / kg
16.3 / 7.3
35.2 / 15.9
Total weight, lbs / kg
22.9 / 10.4
46.7 / 21.2
