Meade TMB-80 manual Mounting Possibilities, Focuser, Finderscope Mounting, Cool Down Times

TMB Optical TMB-80

Thomas M. Back Signature Series

Congratulations on your purchase of our 80mm f/6.3 TMB-80 apochromatic FPL-53 ED triplet refractor. Its truly outstanding optical and mechanical quality will provide you with many years of highly portable observing and imaging enjoyment.

MOUNTING POSSIBILITIES

Your new TMB-80 is usable with many different types of telescope mounts. A suitably sturdy altazimuth mount, such as the Vixen Porta mount, is a good choice for general visual use. The venerable German equatorial mount is also a popular choice, as it can be used for both visual and imaging purposes.

The TMB-80 has a removable L-shaped combined tripod adapter and dovetail mounting shoe. The dovetail is sized and shaped (with slanted sides) to fit the dovetail slot on the head of many equatorial and altazimuth mounts. It will mount without modification directly onto Celestron Advanced Series; Meade LXD-75; and Vixen Great Polaris, Porta, and Sphinx mounts, among others.

In addition, the mounting shoe has two 1/4”-20 thread mounting holes that allow it to be installed on any suitably sturdy camera tripod that has a standard 1/4”-20 thread mounting bolt.

The front hole balances the scope for 1.25” diagonal and eyepiece use with the lens shade extended. The rear hole balances it when a camera or 2” diagonal and eyepieces are mounted. The mounting

Finderscope mounting

point

Focusing scale

on drawtube

Coarse

focus knob

1.25”

accessory

adapter lock knob

Soft brass

compression ring

Camera angle

adjuster (rotating focuser) locking collar

Drawtube lock knob under

focuser

Fine

focus knob

Coarse

focus knob

2” accessory

1.25” accessory adapter lock knob adapter

shoe can also be unbolted, rotated 180° on the scope body, and reinstalled. This will move the balance point further back on the scope body to help balance the TMB-80 if very heavy 2” accessories are used. Cork pads on the underside of the mounting shoe help keep the scope from swiveling when mounted on a tripod.

FOCUSER

Your TMB-80’s backlash-free 2” dual-speed Crayford focuser terminates in a 2” compression ring eyepiece holder. This allows visual use with 2” accessories and imaging with large format CCD cameras. The non-marring soft brass compression ring won’t scratch your star diagonal barrel as an ordinary thumbscrew can.

There is also a 2” to 1.25” compression ring adapter for visual use with 1.25” accessories and for imaging with standard format CCD, webcam, and 35mm photo adapters. The barrel of this adapter is threaded to accept standard 2” filters and has a slight taper at the top that engages the compression ring of the 2” adapter. This prevents the 1.25” adapter from slipping out of the focuser should the 2” focuser’s thumbscrew accidentally loosen during use.

The precision-made focuser has dual-speed focusing. There are two coarse focusing knobs. The right knob also has a smaller concentric knob with a 11:1 ratio reduction gear for microfine focusing. This provides exceptionally precise image control during high power visual observing or 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.

The focuser drawtube has a long 80mm (3.1”) travel. It has a scale marked on the top in 1mm increments so you can note individual focuser positions for easy return to the correct focus when switching between visual use and photography. A knob under the focuser lets you lock in your photographic focus.

Abuilt-in camera angle adjuster (focuser rotation system) lets you rotate the focuser a full 360°. This lets you rotate an attached camera to line up in either a landscape or portrait orientation (or any orientation in between) without losing focus. It also lets you put your star diagonal and eyepiece into the most comfortable observing position as you move from one area of the sky to another. Turn the red ribbed ring at the front of the focuser to the left to loosen the focuser, rotate the focuser to the desired orientation, then turn the red ring back to the right to temporarily lock in the focuser’s new orientation.

FINDERSCOPE MOUNTING

Your TMB-80 is supplied with an attachment point for a quick- release finder bracket on the upper left front side of the focuser. It has a screwdriver-slotted insert that can be unscrewed to provide a mounting point for any of a number of red dot type non-magnifying finders. 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 (for the sharpest and highest contrast images), the optics must be at or very near the temperature of the surrounding air. The “cool down” time needed to reach ambient temperature varies considerably, as the temperature of the scope must change from a typical 72° Fahrenheit indoor temperature to an outdoor temperature that can range from a high of over 100° down to 10° below zero or less. In small doublet refractors, the cool down (or heat up) time is quick, usually less than 30 minutes. In subfreezing temperatures, it may take a small refractor twice that time or more to reach its best performance. This is particularly true with triplet refractors, where the thermal load of the center lens is isolated from the surrounding 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 equilibrium, placing the telescope in an unheated garage for an hour or two before observing can speed up the cool down process considerably. Another technique to shorten cool down time is to retract the insulating dew shield to allow direct exposure of the cell and lens to the night air so they can reach thermal equilibrium faster. Once the lens has cooled, extend the dew shield again. This provides a faster cool down time, and generally will still keep the lens from dewing up. Only on the highest dew point nights will the objective lens form dew on its front optical surface.

The best way to avoid dew forming on the lens after you bring the telescope into the house is to take your closed scope case outside when you observe, so it can also reach ambient temperature. When you are finished observing, cap the 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 the scope away.