camel’s hair brush with attached blower bulb, for example). The use of canned or compressed air should be avoided, if pos- sible, as the propellant in the can may spit out and leave diffi- cult-to-remove deposits on your lens. Also, the expanding com- pressed air drops in temperature as it leaves the can. The cold air coming out of the tiny tube that most compressed air cans
wavefront for third order aberrations, and 1/60th wave for sharp (fifth order) aberrations. It is highly unlikely that even the most ardent observer can see errors of this small a magnitude on an extended object, even under very good seeing conditions (which is when the atmosphere typically presents no better than a 1/4th wave P-V wavefront to the instrument).
TMB Optical TMB-92
Thomas M. Back Signature Series
use to direct the air flow has been known to chill a lens to the point of spalling chips off the lens if pointed at the same spot on the glass for too long.
If you want, or need, to use compressed air to remove stub- born particles, use a high quality compressed air duster (of the R-134 propellant type). ChemTronics sells a high-quality unit. Do not tip or shake the can. Blow any loose particles off the lens surface using short blasts at an angle to the glass, without getting too close to the lens surface or aiming directly at it.
Next, moisten a ball of USP grade pure cotton with a few drops of a photographic-quality optical cleaning solution de- signed for multicoated camera and binocular lenses. You can use Formula MC (available from many telescope dealers) 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 entire surface with the dampened cotton ball or cloth to pick up any stubborn particles and to clean the surface. Ex- change the cotton ball and/or turn the cloth frequently so you always have a clean portion of the cotton ball or cloth in con- tact 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 on the lens. Do not, at any stage, apply hard pressure. Using a fresh piece of cotton or a lint-free white facial tissue, carefully clean the surface of the lens by wiping across in a radial direction. Repeat the process with denatured alcohol, using a blower brush to clean off any
The refractor also presents another factor: the change in spherical aberration with a change in wavelength. This “sphero- chromatism” is found in all refractors. As a lens is tested in the longer (red) wavelengths, the lens becomes “under-corrected.” Tested in the shorter wavelengths (blue), the lens becomes “over- corrected.” These overlapping corrections at different wave- lengths change the star test pattern from technical perfection.
However, TMB objectives are corrected at the peak visual wavelength centered around 560nm in the green-yellow por- tion of the visual spectrum. The eye sees over 80% of the vi- sual detail at this wavelength. It is the correction at this visual peak that makes the difference between a merely good objec- tive and a superb one. Our lenses are figured for the best pos- sible wavefront at green-yellow wavelengths, for the sharpest images and highest contrast.
While star tests are interesting and useful, they should not be the only criterion for judging any telescope’s quality. Most ob- servers spend their nights enjoying the views of extended and detailed objects – like nebulae, galaxies, star clusters, and planets
–not simply examining a star test’s single out-of-focus point of light. We feel that the true proof of optical excellence will be found in your nightly observing, not just in star testing.
A FINAL WORD
Thank you for your purchase of our TMB-92. We believe that this ultra-compact apochromatic refractor will outperform any other telescope type, inch for inch, and is the most trouble- and maintenance-free telescope that you can buy. Its versatility
Congratulations on your purchase of this TMB Optical TMB- 92 Signature Series air-spaced apochromatic triplet refractor. This exceptional 92mm f/5.5 scope uses an element of costly FPL-53 ED (Extra-low Dispersion) glass to achieve true apo- chromatic visual and photographic performance, free from chro- matic aberration and spurious color.
At only 13.25” in length, the TMB-92 is a premium quality ultra-compact refractor that we believe elegantly and more than capably fills the void left by the long-discontinued 90mm Astro- Physics Stowaway (a legendary refractor that sells for up to $6000 on the used market).
The fully-collimatable TMB-92’s truly outstanding optical and mechanical quality will provide you with many years of highly portable visual observing and imaging enjoyment.
PHOTO/VISUAL CONFIGURATIONS
The TMB-92 consists of an optical tube assembly with lens and dew shield, a Feather Touch focuser that slips into the op- tical tube and is locked firmly in place by three brass knobs that allow 360° rotation of the focuser, and
a 2.25” extension tube that can be in- stalled between the optical tube and the focuser for visual use.
When the optical tube and focuser are assembled without the extension tube, the resulting physically short tele- scope configuration provides the long back focus needed by those primarily
focuser rotation.
The supplied carrying case is precut to hold the TMB-92 in either short body imaging or long body visual configurations.
FOCUSER
Your TMB-92 features an ultra-precision Feather Touch Model 3025 dual-speed rack-and-pinion focuser from Starlight Instruments. This exceptionally smooth focuser has a 3” diam- eter drawtube for non-vignetted astrophotography with medium format film cameras and very large chip CCD cameras. The drawtube ends in a 2” accessory adapter with a non-marring compression ring eyepiece/accessory holder that will not dam- age the barrels of your 2” accessories. Three hand-tighten lock knobs on the adapter assure the compression ring’s solid grip on heavy accessory loads. This adapter allows visual use with 2” star diagonals, plus imaging with 35mm film cameras and 2” barrel large format CCD cameras.
The 2” accessory adapter is secured to the focuser drawtube by three recessed hex-head screws. Undoing these allows you to remove the supplied 2” adapter and replace it with a custom- made Feather Touch adapter for medium format (Pentax 6 x 7) film photography using A-P photographic accessories. Please contact Starlight Instruments directly at (847) 985-9595 for any specialized adapters you may need in this regard.
The supplied 2” to 1.25” accessory adapter is designed for visual use with 1.25” star diagonals, plus imaging with stan- dard 1.25” format CCD, webcam, and 35mm adapters. This
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 high-grade acetone will clean the surface to new condi- tion. You may notice a few faint streaks from the dried solvent. They will not affect performance, but they can be removed with light pressure and a Q-Tip slightly moistened with a small amount of alcohol or acetone. Finally, 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 be- fore you start pushing a damp tissue around the lens surface. Clean your optics only when absolutely necessary. If you take proper care of your TMB-92, cleaning should rarely be needed.
THE STAR TEST
We strive to make the best apochromatic optical systems avail- able. You may find your lens may not test “perfect” during an extended and stringently-graded “star test,” particularly if the scope has not fully reached thermal equilibrium before the test. This is not an indication of a poor optic, but is rather due to the test star’s complex wavefront continually changing as the see- ing conditions in our living atmosphere vary from moment to moment.
No optic is perfect, and every brand and model scope will show some error in an extended star test. The sensitivity of the
for visual, photographic, and CCD work is unmatched. With a little care, this fine apochromatic refractor will last you a life- time. Use it to enjoy the wonders of the night sky!
Aperture | BRIEF SPECIFICATIONS |
| | 92mm (3.6”) |
Focal Length | | 506mm |
Focal Ratio | | f/5.5 |
Objective Type | ...................... | air-spaced apochromatic triplet |
| with an FPL-53 ED glass element |
Optical coatings | fully multicoated |
Resolving Power (Dawes’ Limit) | 1.26 arc seconds |
Visual Limiting Magnitude | 12.3 |
Light Grasp Versus the Eye | 173x |
Focuser | Starlight Instruments Feather Touch #3025 |
3” dual speed rack and pinion, with 10:1 ratio fine focus; 2” and 1.25” compression ring eyepiece holders; and 360° rotating camera angle adjuster
Focuser Travel | 2.56” (65mm) |
Tube Diameter | 114mm (4.5”) o. d. |
Minimum tube Length | 13.25” (337mm) |
(set up for imaging, lens shade and focuser retracted) |
Tube Length | 16” (406mm) |
(set up for imaging, lens shade extended, focuser retracted)
Maximum Tube Length | ............................... 20.75” (522mm) |
(set up for visual use, lens shade and focuser extended) |
Optical Tube Weight | 8.5 lbs. (3.86 kg) |
interested in serious CCD imaging us-
ing long equipment trains: camera, filter wheel, adaptive optics system, etc. This arrangement also allows binoviewer use with- out the need for a Barlow or optical compensator lens.
For occasional visual work, a simple optional compression ring extension tube (from Astro-Tech, TeleVue, and others) can be slipped into the scope’s 2” accessory holder to provide the necessary extra physical length to reach focus with a star di- agonal and eyepiece.
For those primarily interested in visual observing and only casual imaging with a 35mm camera, webcam, or Deep Sky Imager-type CCD camera, a 2.25" extension tube (shown above) is supplied to provide the proper back focus for comfortable visual use and casual astrophotography. This extension installs between the optical tube and focuser. A groove in the extension tube engages the large brass lock knobs in the optical tube (that normally control focuser rotation) to lock the extension tube firmly to the optical tube. Three nylon-tipped metal lock knobs
at the opposite end of the extension tube now lock the focuser in place and allow focuser rotation, just as the large brass lock knobs in the op- tical tube do when the extension tube is
Retracted
lens shade
Left coarse
focus knob 
Compression
ring
Focuser rotation/extension tube
lock knob (1 of 3)
2.25” visual extension tube installs here
Hex head
screw
attaching 2”
adapter to
drawtube (2 of 3)
1.25”
accessory lock knob
2”
accessory
adapter
