TMB 105 f/6.2 (CNC Tube)
Price
$3590
Aperture
105 mm
F-Ratio
f/6.2
Focal Length
650 mm
Coatings
Fully Multicoated
Transmission
96+% total transmission
Tube Length
26.5"
Type of Lens
Air Spaced SD Triplet
Weight with Accessories
20.4 lbs.
Weight without Accessories
15.4 lbs
The TMB 105 4” f/6.2 optical tube is a truly international telescope. It is designed by Thomas M. Back in the United States. Its optics are manufactured and multicoated by a Zeiss subcontractor in Russia. The lens cells, tubes, and focusers are manufactured in Germany on computer-controlled milling machines and lathes for absolute precision, extremely tight tolerances, and unit-to-unit consistency. Once the individual optical and tube components have passed their initial testing in Europe, they are shipped to TMB in Ohio for assembly, optical tweaking, and final optical and mechanical testing by the designer himself. Only those optical tubes that pass Tom Back’s personal rigid final inspection standards are covered by the TMB U. S. warranty. TMB telescopes imported into the U. S. through channels other than through TMB itself – and/or through Astronomics, the sole U. S. distributor – are not subject to the designer's inspection and testing and consequently are not covered by the TMB U. S. warranty.
The TMB 105’s super ED apochromatic air-spaced triplet lens provides virtually color-free images across the entire visual spectrum – and beyond, into the infrared, for astrophotography. The Sky & Telescope review commented, “The optical quality of the Russian lens did not disappoint. In side-by-side comparisons with a TMB 100-mm f/8 triplet refractor, the faster f/6.2 instrument showed just the palest rim of color when I viewed stellar diffraction disks inside and outside of focus. The longer f/8 TMB, also with Russian-made optics, was utterly color free right through focus.
”With the f/6.2 scope, the star test revealed an almost complete lack of axial aberrations, with just a trace level of spherical aberration or sphero-chromatism softening the diffraction pattern outside of focus and preventing absolutely identical diffraction patterns inside and outside of focus.
”At 220x (obtained with a TeleVue 3-mm Radian eyepiece) Jupiter and Saturn appeared extremely sharp and contrasty, snapping into focus with an assuredness not seen in lesser telescopes. The lunar limb and crater rims were totally color-free, as was brilliant Venus. The Double-Double was resolved as four dots of light, like tiny drops of white paint set in a black sky, surrounded by the dim ripple of a single diffraction ring. At low power with the 35-mm Panoptic eyepiece, stars were pinpoints across the entire field, except at the very edges, where they began to fuzz out.
“In short, these are optics to please the most discriminating ‘optophile,’ providing, in my opinion, views as sharp as you’ll see in any apo refractor.”
Premium multicoatings on all surfaces assure 99.75% transmission per surface, with a total transmission through the triplet objective in the unusually high 96+% range. The Sky & Telescope review called the optics “immaculately multicoated.”
A large 3" focuser allows for 6x7 medium format astrophotography without vignetting. The focuser rotates 360 degrees with zero image shift to allow a photo to be composed after the camera is focused. The Sky & Telescope review noted that the “rack-and-pinion motion was smooth, without any image shift or backlash.”
The focuser terminates in a removable 3” drawtube to 2” diagonal adapter with a clamping ring to protect the finish of your eyepieces and diagonals from scratches. A 2” to 1.25” clamping ring 2” to 1.25” adapter is also provided. A 3" diameter x 4" long extension tube that mounts between the drawtube and the 3” to 2” adapter provides the correct amount of back focus spacing for visual use with an eyepiece and diagonal. The Sky & Telescope review pointed out about the extension tube that, “unique among refractors, the TMB focuser is designed to accommodate a binocular viewer. Because of their long internal light path through a series of prisms, most binocular viewers require a focuser to be racked in several inches from the normal position, a distance far greater than most focusers provide. But the TMB focuser has a 4-inch-long extension tube that, when removed, allows any binocular viewer to reach focus without any additional optics (usually a Barlow lens) to compensate for the longer light path. Thus, with the TMB scope I was able to enjoy the widest field possible with a binocular viewer, for truly spectacular panoramic and almost three-dimensional views.” Because of the removable extension tube, the total back focus from focuser to image plane is an exceptionally long 220m. The shortest possible tube length is 340 mm with the extension tube removed, while the standard tube length during visual observing is 675 mm. The focuser itself has 70mmm of travel available, so that any focal length eyepiece can be accommodated.
The focuser has large anodized focuser knobs with rubber O-ring gripping surfaces. The Sky & Telescope review noted, “The focuser knobs are a joy – oversize for precise control and each lined on the outer perimeter with five rubber O-rings, which offer a firm grip and frostbite-free handling in cold weather with bare hands. (I can’t fine-focus a camera with gloves on, so this isn’t just a comfort issue with me.) Similarly every lock knob and setscrew is lined with O-rings, each set into a tiny machined groove. This is impressive attention to detail. Furthermore, all the small knobs are interchangeable, providing ‘instant’ spares should you lose a critical lock knob.” The focuser has thermally compensated mechanics so that the motion is as smooth racking in as it is racking out, no matter what the temperature.
The CNC (computer numerical controlled) machined tubes are machined and lathed with extremely tight tolerances to hold the focuser and lens cell in precise alignment The tubes have internal light baffles spaced by aluminum rods for precise positioning to avoid vignetting during medium format photography and when using wide field 2” eyepieces. The tube diameter is 130 mm. There is a retractable 156mm diameter dewcap/lens shade with a thumbscrew lock that slides smoothly over the tube without scratching. The tube and dewcap are painted, the machined metal parts are hard anodized, and the tube rings are satin-finished aluminum castings. The tube rings have flat bosses at the 12 o’clock and 6 o’clock positions to allow an equatorial mount’s dovetail plate to be attached to one side of the rings, while a mounting plate for accessories or guidescope rings is installed on the opposite side. Both mounting bosses have three 1/4”-20 threaded holes with a spacing of 2.36" between the outer holes.
The finder mounting bracket uses a metal-to-metal quick release system for attaching to the scope. The bracket is mounted on the rotating focuser. This allows the focuser rotation to bring the finder scope, focusing knobs, and eyepiece to the most comfortable observing position as a single unit. A fitted, locking hard case measuring 20” x 13” x 9” is provided for carrying the optical tube.
The Sky & Telescope review of the TMB 105 concluded, “I found that the quality of the TMB fittings, along with the size and weight of the telescope, lends a sense of performance and handling that is intangible but immensely satisfying.” For another review, we suggest you follow this link to the non-commercial “Cloudy Nights” review of the TMB 105. The review is extensive, unsparing, and has a number of useful photos.
There are few fast focal ratio apo refractors that reach such rarified levels of hand-crafted optical and mechanical excellence. The TMB 105 is one of them. It follows in the tradition of the Astro-Physics Traveler as an ultra-portable apochromat (it will break down to a length of only 17” and fit into a 20” case, after all). Unlike the Traveler, however, you can have a TMB 105 without having to get on a multi-year waiting list to get one. |
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