Bosma

More Information  · Supplied Accessories  · Images of Some Features Price $198.00 Shipping $20.00 Highest Useful Magnification 156x Visual Limiting Magnitude 12 Focal Length 500mm Focal Ratio f/6.25 Resolution 1.45 arc seconds Aperture 3.15" Warranty 1 year

• 80mm f/6.25 achromatic refractor optics
• 1.25" rack-and-pinion focuser with photographic T-threads
• mounting bar with 1/4"-20 thread holes for use on the supplied light-weight full size photo tripod
• 45° viewing-angle 1.25" image-erecting diagonal
• 10mm and 25mm 1.25" Plössl eyepieces
• 5 x 24mm correct image finderscope
• padded soft case
• Moon filter and genuine Baader Solar Film solar filter

The Bosma Beta is a very complete and very inexpensive telescope that has been named an Official Product for the International Year of Astronomy 2009. One of only two telescopes named Official Products by the IYA 2009, it was chosen for its exceptional versatility, completeness, portability, and affordability. You can use your Bosma Beta for observing the heavens at night, viewing sunspots during the day, and scanning the wonders of nature on our planet any time you choose.

The images through the Bosma Beta’s 500mm f/6.25 achromatic doublet optics are surprisingly good for such an economical scope, even at high magnifications. The two supplied Plössl eyepieces give you magnifications of 20x and 50x, and other optional eyepieces can extend your power range in both directions, as low as 12.5x and up to a practical maximum of over 150x.

The lightweight Bosma Beta is an ideal scope for spur of the moment observing and travel. The Bosma Beta weighs only 3.6 pounds, well-matched to its supplied lightweight (3.5 pound) full-length photo tripod. With a total weight of little more than 7 pounds, the Bosma Beta can be left set up on its tripod and taken out to observe at a moment’s notice day and night, even by a child.

Because of its light weight and compact size, the Bosma Beta can be piggybacked on a larger telescope and used as a photoguide scope for long exposure astrophotography. Its rack-and-pinion focuser terminates in standard 42mm T-threads so you can add an optional T-ring and a 35mm or DSLR camera to turn the scope into a 500mm telephoto lens for lunar and terrestrial photography.

Other features of this IYA 2009 Official Product include an image-erecting star diagonal with a comfortable 45° viewing angle for day and night observing, a 5 x 24mm correct-image finderscope, filters for both solar and lunar observing, and a soft carrying case.

Features of this Bosma Telescope . . .

• Achromatic refractor optics: 80mm (3.15") aperture, 500mm focal length, f/6.25 focal ratio doublet lens with anti-reflection coatings on all air-to-glass lens surfaces for high light transmission and contrast.

• Full power range capability: The Bosma Beta comes with two good quality four-element 1.25" Plössl eyepieces. The supplied 25mm Plössl gives you a magnification of 20x, with a big 2.5° field of view for terrestrial and lunar observing. With its wide field and a generous 4mm exit pupil, it will also show you dozens of faint deep space nebulas and open star clusters. The supplied 10mm Plössl gives you a magnification of 50x for lunar close-ups; the beginnings of planetary observing (the rings of Saturn and some of the storm bands on Jupiter are visible at this power, even though the planets will still appear quite small at 50x); and nice views of globular star clusters, smaller nebulas, and even some galaxies.
      The “highest useful magnification" is 156x. This is the power you will get with an optional 3.2mm eyepiece, which provides an exit pupil of 0.5mm (about 1/50th of an inch) and 49.5x per inch of aperture. This is generally the maximum power per inch of aperture and smallest exit pupil recommended with any telescope before the images start to become too dim to be consistently useful. An optional 5mm eyepiece providing 100x (or a 2x Barlow lens doubling the 50x power of the supplied 10mm eyepiece) would probably be a more usable magnification for everyday use. The lowest useful power is 12.5x, which you can reach with a 40mm eyepiece. Most Plössl eyepieces will give you a 3.4° field at that power, nearly 7 times as wide as the full Moon.

• 1.25" rack-and-pinion focuser with photographic capabilities: The focuser has a 1.25" eyepiece/accessory adapter to hold the supplied star diagonal. In addition, the 1.25" drawtube has standard 42mm T-threads at the accessory adapter end. This lets you connect a 35mm film camera or DSLR directly to the Bosma Beta, simply by adding an inexpensive optional T-ring to fit your particular camera. This converts the Bosma Beta into a fast 500mm (10x) f/6.25 telephoto lens for terrestrial and lunar imaging.

• 1.25" image-erecting 45° star diagonal: The supplied 45° viewing angle 1.25" star diagonal contains an image-erecting prism that shows you images that are right side up and correctly oriented left to right (so that printing is readable, for example). Conventional 90° star diagonals in refractors show mirror images, while an eyepiece in a reflector will show images that are upside-down and backwards. The image-erecting diagonal of the Bosma Beta makes it easier to find your way around the sky, since the way you see the sky in the Beta’s eyepiece is the way you see it when you look at the sky with binoculars or your bare eye, or when you look at a star chart.
      In addition, the 45°viewing angle is more comfortable for extended viewing sessions and for terrestrial viewing. It also makes it easier for observers of different heights to use the scope without having to adjust the tripod height each time a different observer steps up to the eyepiece.

• 5 x 24mm correct-image finderscope: Like the image-erecting star diagonal above, the supplied straight-through 5 x 24mm finderscope contains an image-erecting prism that shows you images that are right side up and correctly oriented left to right. Conventional finderscopes show images that are upside-down and backwards. Like the star diagonal, the correct-image finder of the Bosma Beta makes it easier to find your way around the sky, since the way you see the sky through it is the way the sky is oriented on a star chart.

• Solar and lunar filters: The Bosma Beta comes with two filters that make it easier to view the Sun and Moon. The first is a 1.25" Moon filter that threads into the base of your eyepieces to reduce the glare of the brightly-illuminated Moon that can wash out small details on our nearest celestial neighbor.
      The second filter, available only for a limited time as an IYA 2009 bonus, is a solar filter that lets you see sunspots (many larger than the Earth itself) as they grow and march across the face of the nearest of all stars, our Sun. The filter is a cap that fits snugly over the front of the Bosma Beta. The cap has a central aperture containing a safe-viewing filter element of genuine Baader Solar Film to fully protect your eyesight from the Sun’s energy. WARNING: Never look at the Sun through the Bosma Beta without installing the solar filter firmly in place and covering the objective lens of the finderscope. Failure to use the filter properly, and to cover the finderscope objective, can cause instant and irreversible eye damage.

• Mounting dovetail and tripod: The Bosma Beta has a built-in tripod adapter with 1/4"-20 thread mounting holes that allow it to be installed on the supplied camera tripod.
      The lightweight and compact supplied tripod has three-section black anodized aluminum legs. The tripod weighs only 3.5 pounds, which means that carrying it won’t be a problem, even with the 3.6 pound Bosma Beta scope attached. The legs are tipped with rubber caps for a non-skid grip on smooth surfaces. Flip-lever leg locks provide fast set-up and takedown. When the legs are open, a knob at the bottom of the center post clamps the legs’ spreader bars firmly in place to improve the tripod’s stability. A knob locks the crank-operated geared rising center post in place at the desired height.
      The integrated pan head has 3-way motion (up/down, right/left, and a 90° swing up to change from a landscape to portrait orientation for photographic composition). A pan arm permits precise control over the scope’s motion. Twisting the pan arm locks the vertical tilt (altitude) at any desired angle and adjusts the vertical drag to keep the scope from tilting suddenly when the pan arm is released. A separate knob locks the pan (right/left) motion and adjusts the drag in azimuth, while another knob locks the swing-up camera platform at a landscape or portrait orientation (or at any angle in between). The pan head is not fluid damped, but the pan and tilt movements are smooth enough for cleanly tracking moving subjects on the ground as well as the motion of the stars and planets across the heavens.

• Carrying case: The scope comes in a padded soft carrying case with shoulder strap that holds scope and accessories. The case makes it easy to take the Bosma Beta with you when you travel, whether it’s out to your backyard or on a plane trip around the world.