Meade Instruments TMB Optical TMB-130 - Manual (Page 2)

Your Feather Touch focuser has dual-speed focusing.
There are two coarse focusing knobs. The right knob also
has a smaller concentric knob with a 10:1 ratio reduction
gear for microfine focusing. This provides exceptionally
precise image control during high power visual observing
and critical film or CCD imaging. The focus knobs have
ribbed gripping surfaces so they are easy to operate, even
while wearing gloves or mittens in cold weather.
Your focuser drawtube has a long 110mm (4.33”) travel.
It has two scales (one on either side) that are laser-engraved
in 1mm increments. These let you note individual focuser
positions for easy return to the correct focus when switch-
ing between visual use and photography.
Because your Feather Touch focuser is so smooth in
operation and moves so freely, it can only hold a limited
amount of weight (generally about 1 lb.) without drifting
out of focus when the focuser drawtube is not horizontal
and has a significant vertical component. The focuser there-
fore contains an adjustable-tension internal brake system
to allow astrophotography and visual use with heavy eye-
pieces without the possibility of focus shift.
The brake consists of a lever arrangement within the
focuser’s pinion block. Adjusting the thumbscrew under-
neath the pinion block causes the lever to press a friction
pad onto the pinion. This increases the torque needed to
turn the focus knobs. If the thumbscrew is turned all the
way in (only 1 to 1½ turns), the pinion shaft and drawtube
are locked into position at the desired focus for long expo-
sure imaging. Visually, partial tightening of the internal
brake offers a virtually infinite range of braking force to
accommodate various eyepiece and accessory weights.
A built-in camera angle adjuster (focuser rotation sys-
tem) lets you rotate the focuser a full 360° without losing
focus. This lets you rotate the focuser to line up a camera
in either a landscape or portrait orientation (or any orien-
tation in between). It also lets you put your star diagonal
and eyepiece in the most comfortable observing position
as you move from one area of the sky to another.
Three focuser rotation handles and recessed finger grips
in the locking ring around the front of the focuser body let
you adjust the focuser rotation angle. While holding the
2” accessory adapter of the focuser steady with one hand,
use the rotation handles to turn the locking ring slightly
counterclockwise to unlock the focuser. Rotate the focuser
to the desired new orientation. While again holding the 2”
accessory adapter steady, turn the locking ring back clock-
wise to lock the focuser in place at the new angle.
Your focuser drawtube glides on three stainless steel
straps that mate with Teflon bearing surfaces to provide
very tight yet extremely smooth motion. This design elimi-
nates the need for grease between the housing and draw-
tube. A greaseless drawtube prevents the collection of dirt
that may eventually cause problems between these surfaces,
so no routine focuser maintenance is required except for
an occasional wipe down of the drawtube with a soft cloth.
FINDERSCOPE
No finderscope is provided with your TMB-130. How-
ever, there are two holes for a finder bracket drilled and
tapped on 1.25” centers at the 10 o’clock position on the
rear of the focuser. These holes will accept any of a num-
ber of finderscope mounting rings. Contact your telescope
dealer for an appropriate finder if you do not already have
one that is suitable.
COOL DOWN TIMES
For any optical system to give its best wavefront (sharp-
est and highest contrast images), the optics must be at or
very near the temperature of the surrounding air. This “cool
down” time needed to reach ambient temperature varies
considerably, as the temperature of the telescope must
change from a typical 72° Fahrenheit indoor temperature
to an outdoor temperature that can range from a high of
over 100° down to 20° below zero or less.
With small doublet refractors, the cool down (or heat
up) time is quick, usually less than 30 minutes. In larger
refractors, or in subfreezing temperatures, it can take a tele-
scope one to two hours to reach its best performance. This
is particularly true with triplet refractors, where the ther-
mal load of the center lens is isolated from the surround-
ing air by the lenses on either side of it. This slows the
transfer of the center lens heat load to the outside air.
If you’d like to shorten the wait to reach thermal equi-
librium in backyard observing, place your telescope in an
unheated garage for a few hours before observing. This
can shorten the cool down process considerably.
Another technique for shortening cool down time in
the field is to retract the dew shield to allow direct expo-
sure of the lens cell and lens to the night air so they reach
thermal equilibrium faster. Refractors show a noticeable
undercorrection during cool down. By comparing a star’s
image on both sides of focus you can determine when the
images are similar and the lens is near optimum correc-
tion. At this point, slide the dew shield back out to its fully
extended position. This provides a quicker cool down time,
and will generally still keep the lens from dewing up.
Only on the highest dew point nights will the objective
form dew on the front optical surface. If you live in a high
humidity climate, however, we recommend the regular use
of a dew heater strip.
The best way to avoid dew forming on the lens after
you bring your telescope into the house is to take your
closed telescope carrying case outside with your scope,
where the case can also reach ambient temperature. When
you are finished observing, cap your telescope with its dust
caps and place it into the carrying case. Bring it into the
house and let it slowly warm back up to room temperature,
then remove the dust caps to allow any trace of dew to
evaporate. Once the objective is free from dew, replace
the dust caps and store your scope away.
CLEANING
The best policy is not to let your lens get dirty and/or
dusty in the first place. The use of the dust caps is highly
recommended. However, no amount of preventative mea-
sures will stop the objective from eventually collecting dust
and airborne pollutants on the first optical surface.
We recommend that you do not clean the objective too
often, no matter how frequently the urge to do so may hit
you. A few specks of debris on the lens will not be visible
in your images, as they are not in the focal plane. They
don’t block enough light to measure, let alone be seen.
Depending on how often you use your scope, and the
amount of pollutants in your air, you may have to clean
your scope as often as twice a year, but generally no more
than that – and preferably no more than once a year. If the
front lens surface becomes dusty, smeared, or shows fin-
gerprints or any other surface build-up, and you find it
absolutely necessary to clean the lens, use the following
technique to clean it.
First, gently blow away any surface dust or particles
with a clean air blower (a child’s ear syringe or a
photographer’s camel’s hair brush with attached blower
bulb, for example). The use of canned or compressed air
should be avoided, if possible, as the propellant in the can
may spit out and leave difficult-to-remove deposits on your
lens. Also, the expanding compressed air drops in tem-
perature as it leaves the can. The cold air coming out of
the tiny tube that most compressed air cans use to direct
the air flow has been known to chill a lens to the point of
spalling glass chips off the lens if pointed at the same spot
on the lens too closely for too long.
If you want, or need, to use compressed air to remove
stubborn particles, use a high quality compressed air duster
(the R-134 propellant type). ChemTronics sells a high-
quality unit. Do not tip or shake the can. Blow any loose
particles off your lens surface using short blasts at an angle
to the glass, without getting too close to the lens surface or
aiming directly at it.
Moisten a ball of USP grade pure cotton with a few
drops of a photographic-quality optical cleaning solution
designed for multicoated camera and binocular lenses. You
can use Formula MC (available from many telescope deal-
ers) or your own mixture of distilled water and a drop or
two of mild soap. A well-worn 100% cotton handkerchief
also works well and Zeiss and Kodak both make suitable
cleaning fluids. Blot the lens surface with the dampened
cotton ball or cloth to pick up any stubborn particles and
to clean the surface. Exchange the cotton ball and/or turn
the cloth frequently so you always have a clean portion of
the cotton ball or cloth in contact with the lens.
Use a very small amount of liquid – not so much that
the fluid could be wicked between the lenses by capillary
action. Do not drip the cleaning fluid directly onto your
lens. Do not, at any stage, apply hard pressure. Using a
fresh piece of cotton or a lint-free white facial tissue, care-
fully clean the surface of the lens by wiping from the cen-
ter to the edge in a radial direction. Repeat the process
with denatured alcohol, blowing off any dust that may fall
on the lens as you are cleaning it.
If you want to take the ultimate step in cleaning, a final
rinse with HPLC grade acetone, or any high-grade acetone,
will clean the surface to new condition. You may notice a
few faint streaks on the lens from the dried solvent. They
will not affect performance, but can be removed if desired
with light pressure and a Q-Tip slightly moistened with a
small amount of alcohol or acetone. Finally, a few short
blasts of air from a clean air blower bulb can be used to
remove any remaining dust.
Avoid overcleaning your scope. The multicoatings on
the lens are quite hard and durable. However, frequent
overzealous cleaning can scratch the coatings if all the dust
particles (which are often tiny flecks of windborne rock)
are not removed before you start pushing a damp tissue
around the lens surface. Clean your optics only when ab-
solutely necessary. If you take proper care of your scope,
cleaning should rarely be needed.
COLLIMATION
Your telescope was carefully collimated prior to ship-
ment to your dealer. With normal care the optics will keep
that alignment permanently. However, if the telescope takes
a very strong blow in shipping or while transporting it to
your observing site, there is the small possibility that you
may have to recollimate the lens. The lens cell has three
pairs of push-pull collimating screws that will allow you
to collimate it using a metric Allen wrench.
To gain access to the collimation screws, remove the
black trim ring/knife-edge baffle from the front of the dew
shield by unthreading it in a counter-clockwise direction.
Set it aside and push the dew shield back on the optical
tube until the front of the dew shield clears the lens cell
and exposes the collimation screws at the rear of the lens
cell, as shown in the illustration below.
We recommend either of two collimation methods. In
the first, a “Cheshire” eyepiece (available from Tectron or
your telescope dealer) is inserted directly into the eyepiece
holder (without using a star diagonal). The Cheshire method
can be used indoors or in the field, day or night.
The dust cover is placed over the lens cell to seal the
objective end of the scope and keep light from entering
the optical tube. A bright light source is aimed at the open-
ing in the side of the Cheshire eyepiece. You can use the
light from the sky outdoors during the day. At night or in-
doors, aim the light of a flashlight directly at the opening
in the side of the Cheshire.
Look through the hole in the end of the Cheshire. You
will see a series of faint circles of reflected light against a
black background. If the circles of light are all concentric,
your scope is in collimation. If the circles of light are not
concentric, adjust the push-pull collimation screws until
you line up the off-center circles to form a single round
circle. The illustration on the next page shows a close-up
of one of the pairs of collimation screws.
The taller screw is the actual collimation screw, while
Dew shield
fully
retracted
Collimation screws
(1 pair of 3)
Lens cell
Trim ring /knife
edge baffle
removed from
dew shield
How to
access the
collimation
screws