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Above: Astro-Physics 90mm Telescope installed onto an optional tripod, with optional "Maxbright" Diagonal and 1.25" Eyepiece (70748 bytes).
Announced in June 1999 as a very limited production item, the long awaited Astro-Physics 90mm "Stowaway" telescope has evolved from an 90mm f7 doublet concept into a 14 inch long, 6 lb., 92.5mm aperture 450mm f4.9 triplet Apochromat telescope. It is very likely that not many people will ever see this 90mm telescope displayed at any other location than our Laurel, Md. showroom or, at our Internet site since this first production run is extremely limited in numbers made to prove the concept, and it is not likely to remain in regular production. If you are interested in a telescope such as this, then you should contact Company Seven for advice about availability or alternative telescopes.
The 90mm f5 telescope is the culmination of years of optical research by Roland Christen of Astro-Physics. This effort aimed at developing a very fast and portable multi purpose telescope that will allow you to enjoy sharp, high-contrast images wherever you go.
Notes on the 90mm f5 by Roland Christen:
In the production version, we kept the original 3-element APO lens design, added about 2mm to the clear aperture (it is really a 92mm refractor) and developed a brand new 2 inch focuser with coarse and fine-adjustment to allow critical focusing at high power.
How does the lens work on astronomical objects? It's one thing to be a superb day-time instrument, but this lens works extremely well on night-time objects. It is, after all, a similar design to the famous Traveler EDF lens. With a 40mm wide-field 2 inch eyepiece, it will show almost 6 degrees of sky at 11x. On the other end of the power range, with a 3x Barlow and 4mm eyepiece (337x), I was able to easily split a number of double stars in Bo×tes, Hercules and Cygnus down to 1.2 arc seconds, and elongate one at 0.9 arc seconds. The two unequal doubles of Epsilon Bo×tes and Beta Cygnus showed beautiful, clean separations with pearl-like star points.
Recently on Mars, I easily made out the North Polar Cap and the dark ring around it. I observed disc detail on the ball of the planet. There were prominent white clouds on the edge of the morning side and near the south polar regions. This observation was well after opposition when the planet was down to 12 arc seconds diameter.
In short, I am very pleased with how well this small telescope performs with such a short focal ratio. There is nothing else like it on the market today and this limited production run will become an heirloom for sure.
The "Stowaway" 90mm multipurpose telescope resembles the Astro-Physics 105mm "Traveler" EDF telescope with its compact f5 frame, and collapsing Lens Shade to insure compact storage, but differs from the 105 in having:
The telescope design and manufacturing process ended up costing about as much as the larger 105mm Traveler telescope since the amount of labor was about the same (or a bit more to "tool up"), the new focuser accepts up to 2 inch diameter accessories and is actually more complicated than the traditional Astro-Physics 2.7 inch focuser, and there is not that much difference in the other costs of materials.
The objective's two air to glass surfaces have a multi-layer anti-reflection coatings that improves overall light transmission to greater than 97% in the visual wavelengths. So, the system has about 169 times the light gathering power of the unaided human eye making it through the objective lens. On most nights, the settling down time for the lens is on the order of minutes, and even in sub-freezing conditions it rarely requires more than 30 minutes to acclimate from typical room temperature.
The lens is so well figured that it is capable of operating at 300X or more cleanly with optional eyepiece lenses; this reaches well into that threshold necessary to routinely obtain meaningful views of the planets; showing several bands and their shades of color (beige, tan, browns) on Jupiter, the Cassini division on Saturn, the polar cap on a fiery red Mars. With an eyepiece that shows 1/2 degree field or so, or the optional Binocular Viewer take a walk on an apparently three dimensional Moon! Or, follow its terminator throughout the moons phases (optional neutral density filter suggested to tone down its brightness). The 90mm should resolve objects on the moon as small as 4.8 km in diameter; it will see the four largest moons of Jupiter and their shadows cast as a small round disc on the cream, beige and tan colored surface of Jupiter when they transit past the planet!
With a matched wide angle ocular the "Stowaway" reveals its extraordinary wide field of view ability showing up to 5.7 degrees actual field of view at 8X to reveal the entire "Messier Catalog" of deep sky wonders, or to be employed for panoramic viewing of a seashore or countryside. Imagine a telescope that at a dark sky site has the combination of resolving power and field of view to sweep the Milky Way, see the Double Cluster in Perseus (NGC-869), find the Andromeda galaxy (M-31) and see it's ellipsoid shape, and see the form of large Nebulae such as the Veil and North American Nebulae! With an optional TeleVue Optics 22mm Nagler Type 4 or the 35mm Panoptic ocular the "Stowaway" can reveal all three stars of Orion's belt, closer in it reveals the jewel like stars of the Trapezium - a birthplace of stars, with a sweeping wisps of greenish gas clouds surrounding it. With a higher magnification M13 (the Hercules star cluster) takes on a "salt and pepper" appearance even from suburban skies on a clear night. By the time one finds a large enough aperture catadioptric, reflecting, or achromatic refractor to see similar detail, then one can only see a fraction of their area due to the relatively high focal length of these competing telescopes; imagine trying to observe the night sky through a straw!
The 90mm "Stowaway" compares favorably against many telescopes in field of view:
In fairness, the cost of the "Stowaway" (equipped with either an optional Alt-Az or Equatorial mount) is positioned at a higher cost than most of the above telescopes. And as a practical matter for some applications in astronomy the nominal match of the "Stowaway's" exit pupil to an average human eye will be obtained at magnifications of between 17X and 13X, while the best performance will be obtained at all magnifications if a wise choice of well corrected oculars is made - this is not attainable with several of the simpler eyepiece designs. Also consider that an optional good quality "Barlow" amplifying (negative) lens, or long eye relief TeleVue "Radian" oculars (also introduced in 1999) will usually be put into use to attain the highest use able magnifications.
Optional camera adapters are available to employ the telescope for film photography, or for CCD imaging operations (such as is possible with our SBIG CCD systems. Techniques and hardware permit imaging of the planets, moon, or deep sky wonders, or of terrestrial wildlife over a wide range of magnifications.
With optional 2 and 3 inch long, 2 inch diameter extension tubes it is possible to use the telescope to observe at at very close distances as a "long distance microscope".
A particular joy of this instrument is that with a suitable mount is at the limit for those who prefer a completely "carry-on luggage" degree of portability. Few larger refractors may be carried on, but then these will require a notably heavier mount that must be packaged and checked in separately. Furthermore, this is a telescope which one can grow with since most of the accessories that one would buy for this telescope are upwardly compatible with any larger telescope that one is likely to buy at Company Seven.
An optional 90 degree mirror diagonal will provide a comfortable viewing position for the observer by diverting the image at the rear of the telescope off axis by 90 degrees to the side, with minimal degradation of image quality. The view when using the telescope as it is provided will appear to be right side up, and is reversed left to right; this is not usually a problem for astronomy or nature observing because the image quality provided by the high quality mirror and 2 inch diameters panoramic oculars is exceptional.
While Company Seven does offer optional 45 degree inclined image erecting prisms, these prisms can only accommodate 1.25 inch oculars. Furthermore, the erecting prisms will not provide image quality to equal that of a good mirror diagonal, this is particularly perceptible at higher magnifications. However, for moderate to medium magnification applications where one needs correct images (such as to read numbers, etc.) then the prism should be suitable.
Left: Astro-Physics 2" Focuser with coarse (Black knob) and fine (Brass knob) geared reduction. Smaller silver knob at on Focuser Housing is Drawtube Lock Screw, on Drawtube to the left is 2" Accessory Set Screw. The Astro-Physics Maxbright Diagonal shown here is optional. (41,274 bytes). Click on image for englarged view (385,643 bytes)
The mechanical construction of the Stowaway telescope is completely trouble-free and keeps the optics permanently aligned. It's optical tube assembly is precision machined in house with the most modem CNC equipment available; there are no fragile die casts in this telescope. Expert machinists transform solid, aircraft-quality aluminum into a fully baffled tube assembly. Astro-Physics staff has endeavored to achieve the highest absorption of stray light possible to provide the user with maximum contrast. The textured off white optical tube, and black anodized focuser will retain their beauty for many years. You will appreciate the unique design and fine craftsmanship of this telescope.
This new Astro-Physics 2 inch focuser is a very finely crafted unit with several unique features. The components are machined to extremely high tolerances, assuring that there is no wiggle between the drawtube and housing. Knife edge baffles are machined into the walls of the telescope optical tube and of the focuser drawtube, these and painted flat black in order to maximize contrast by essentially eliminating any internal reflections. The inside diameter (I.D.) of the drawtube is 2 inches thus permitting the avid astrophotographer to employ up to a 35mm format film or CCD camera to capture images with minimal vignetting. You can use standard 2 inch accessories, and with the furnished 1.25 inch adapter (threaded for 48mm filters) use common oculars and accessories too. Recessed brass locking rings are installed at each thumbscrew location; as you tighten a thumbscrew a brass locking ring clamps onto the part that has been inserted; consequently the focuser drawtube and any accessories are held securely in place and will not mar the surface of your accessories. This is particularly important considering the heavy and expensive accessories that you may use.
We invite you to compare the optical performance and mechanical construction of any other scope of comparable size on the market today. You will find that the Astro-Physics 90mm "Stowaway" is the best performing telescope of its size.
|Color correction:||Less than 0.01% focus variation from 650nm to 430nm|
|Clear aperture:||92.5mm (3.64")|
|Focal length:||450mm (17.7") (actually f4.9)|
|Resolution:||1.24 arc seconds|
|Coatings:||Multi-layer, overall transmission greater than 97% in peak visual wavelengths|
|Magnification range:||8x to 330x|
|Tube assembly:||White/Black finish, aluminum tube; fully baffled, permanently aligned cell construction; engraved focuser|
|Focuser type:||2.0 inch Astro-Physics rack and pinion focuser, 2.2 inch travel; 2" to 1.25" reducer|
|Focuser Gearing:||Coarse, and Fine Focus with 10:1 Reduction|
|Telescope length:||35.6cm (14") with dewcap fully retracted|
|Weight with Lens Shade/Dewcap:||6.5 lbs. (3 kg)|
|Carrying case type:||Custom padded bag|
|Case outside dimensions:||17"x 11" x 5" (43cm x 28cm x 13cm)|
|35mm prime-focus field:||4.4 x 3.0 x 5.3 degrees @ f5|
|35mm telecompressor field:||5.4 x 3.7 degrees @ f4.|
|35mm field with 2x Barlow:||2.2 x 1.5 degrees @ f9.9|
|Eyepiece||Magnification||Actual field of view||Exit pupil|
|35mm Panoptic||13x||4.82 degrees||7.0mm|
|27mm Panoptic||17x||3.8 degrees||5.4mm|
|22mm Nagler Type 4||21x||3.9 degrees||4.4mm|
|22mm Panoptic||21x||3.1 degrees||4.4mm|
|12mm Nagler Type 4||38x||2.1 degrees||2.4mm|
|6mm Radian||77x||0.62 degrees||1.21mm|
|4mm Radian||115x||0.42 degrees||0.8mm|