Your TMB-80CF is usable with many different telescope mounts. It comes with two 90mm felt-lined hinged split mounting rings that have five 1/4”-20 thread holes drilled and tapped into the top and bottom of each ring. You can use these to install the scope directly on many German equatorial mounts, or on a telescope mount dovetail plate such as those from Losmandy or Vixen. They also let you mount an accessory plate on top of your scope.
A quality altazimuth mount, such as the Astro-Tech Voyager or Vixen Porta mount, would also be a good choice for grab-and-go visual use. Either mount can be used with the TMB-80CF simply by adding a Vixen-style dovetail plate to the tube rings.
FOCUSER
Your focuser is a backlash-free dual-speed 2” Feather Touch Crayford from Starlight Instruments. Its drawtube terminates in a 2” compression ring accessory holder to allow visual use with 2” accessories and imaging with large format CCD cameras. The non- marring soft brass compression ring won’t scratch your 2” 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. Its barrel is threaded to accept standard 2” filters and has a slight taper at the top that en- gages the compression ring of the 2” adapter. This prevents the 1.25” adapter from slipping out of the focuser should the two 2” accessory holder thumbscrews accidentally loosen during use.
Your focuser has two coarse focusing knobs. The right knob has a smaller concentric knob with a 10:1 reduction gear microfine focusing ratio. This provides precise focusing during high magni- fication visual observing and critical 35mm or CCD imaging. The focus knobs have ribbed gripping surfaces so they are easy to op- erate, even while wearing gloves or mittens in cold weather.
Because the 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 tilted vertically. The focuser therefore contains an adjustable ten- sion internal brake system to allow astrophotography (and visual use with heavy eyepieces) without the possibility of focus shift.
A knob under the focuser lets you adjust the tension on the draw- tube to accommodate differing equipment payloads. If the thumb- screw is turned all the way in (only 1 to 1½ turns), the drawtube is locked in position for long exposure astrophotography. Partial tight- ening of the knob offers a virtually infinite range of braking force to accommodate various eyepiece weights for visual use.
FINDERSCOPE MOUNTING
Your scope’s carbon fiber body does not have any attachment points for a finderscope bracket. However, the 1/4”-20 holes in the top of the tube mounting rings offer several possible mounting locations for an optional finderscope. However, it is worth noting that the scope’s short focal length, combined with the wide fields of many eyepieces, makes the TMB-80CF its own best finderscope. For example, a 2” 40mm TMB Paragon eyepiece on the TMB- 80CF yields a wide 5.4° field at 12.6x, thereby converting the scope into the optically finest 80mm superfinder ever made.
COOL DOWN TIMES
For any optical system to perform at its best, the optics must be at or very near the air temperature. The “cool down” time needed to reach this ambient temperature varies considerably, as the scope
2” accessory lock knob
(2 of 2)
Coarse
focus
knobFine focus
knob
| 1.25” | | 1.25” accessory | Coarse |
| accessory | |
| Drawtube | focus |
| lock knob | adapter |
| lock and brake | knob |
| |
| | |
| | adjustment knob | Focuser Features |
| | under focuser |
temperature must change from a typical indoor temperature of 72° Fahrenheit to an outdoor temperature that can range from a high of over 100° down to 10° below zero or less. In 80mm refractors, the cool down (or heat up) time in most situations is often quick, usu- ally less than 30 minutes. In subfreezing temperatures, though, it may take an 80mm refractor twice that time or more to reach peak performance. This is particularly true with a triplet like the TMB- 80CF, where the thermal load of the center lens is isolated from the open air by the lenses on either side of it. This slows the trans- fer 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 shorten the cool down process considerably. Another technique is to retract the dew shield to allow direct expo- sure of the lens to the night air so it 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 dew shield is oversized, with a 124mm o.d. compared to the 80mm lens diameter and 90mm tube diameter. This assures that tube currents, which typically follow the walls of telescope tubes and dewshields, will be out of the 80mm light path for the most part and will have only a minimal effect on your images as your scope cools down to ambient temperature. You can begin serious observing sooner with your TMB-80CF than you can with an alu- minum tube 80mm triplet with a conventional dew shield design. A lock knob built into the dew shield lets you lock the dew shield firmly in place so it can’t slip down while aiming at the zenith.
The best way to avoid dew forming on the lens after you bring the scope 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.
CLEANING
The best policy is not to let the lens get dirty and/or dusty in the first place. The regular use of the dust caps is highly recommended. However, no amount of preventative measures will keep your ob-
