Cometron FirstScope 76, 3" tabletop altazimuth reflector

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The very sensibly priced Celestron Cometron FirstScope 76 reflector is designed for beginning or casual astronomers who want to experience for themselves a dazzling comet, star cluster, or nebula . . . without spending a fortune. This Celestron FirstScope 76 Dobsonian-style tabletop telescope is lightweight and portable, making it a great grab-and-go telescope for spur-of-the-moment observing. It has a simple design that makes it easy for beginners to use, and its no-tool setup means you are up and observing in no time.

The FirstScope 76 has a spherical mirror with a generous 76mm aperture that gathers 118 times as much light as the sharpest eye. This provides bright, sharp views of faint celestial objects and shows the Moon’s mountains and craters in crisp detail. And, thanks to its wide field of view, you’ll be able to observe comets and even favorite deep-sky objects like the Orion Nebula.

Weighing just 4.3 pounds, the compact Celestron Cometron FirstScope 76 is a tabletop telescope that you can pick up with one hand and take out to observe whenever the urge strikes you. It’s also stylish enough to be a decorative fixture on your bookshelf or desk.

This Cometron FirstScope’s Optical System . . .

Reflector optical tube: 76mm (3”) aperture 300mm focal length f/3.95 spherical mirror Newtonian reflector. The mirrors are aluminized for high light transmission and overcoated with durable silicon dioxide (quartz) for long life.

Rack and pinion focuser: The 1.25” focuser has dual focusing knobs for precise image control with either hand. The large focus knobs are easy to operate, even while wearing gloves or mittens in cold weather.

Two eyepieces: You get two 1.25" Kellner eyepieces: a 20mm (15x) with a 3° field of view (six times the diameter of the full Moon for wide angle views) and a 10mm (30x) with a 1.5° field of view (three times the diameter of the full Moon for more close-up views). Both eyepieces have antireflection coatings on their lens surfaces for sharp images and good contrast.

Finderscope: A low power 5x24mm finderscope attaches to the side of the optical tube. The straight-through viewing refractor finderscope provides a traditional inverted mirror-image astronomical view. If properly collimated (aligned) with the view through the main telescope, its crosshairs will help you center distant objects in the telescope so you don’t have to search for them using the narrower eyepiece field of view.

This Cometron FirstScope’s Mount . . .

Dobsonian-type tabletop mount: The simple and durable painted fiberboard altazimuth mount has rubber feet that lets it sit securely on a tabletop or any other suitable horizontal surface. The compact and lightweight mount weighs only 4.3 lbs (1.95 kg). It provides smooth right/left and up/down manual motion of the optical tube. This is suitable for low power casual astronomical observing, and will let you easily track objects as they move across the sky. 

The large knob that connects the 10" long optical tube to the mount allows you to adjust the friction on the scope in up/down motion. This lets you control how smoothly the mount moves as you manually push the tube to follow objects moving through the sky.

Two year warranty: As an expression of Celestron’s confidence in the quality of their products, the Celestron Cometron FirstScope is protected by Celestron’s two-year limited warranty against flaws in materials and workmanship.
Highest Useful Magnification:
This is the highest visual power a telescope can achieve before the image becomes too dim for useful observing (generally at about 50x to 60x per inch of telescope aperture). However, this power is very often unreachable due to turbulence in our atmosphere that makes the image too blurry and unstable to see any detail.

On nights of less-than-perfect seeing, medium to low power planetary, binary star, and globular cluster observing (at 25x to 30x per inch of aperture or less) is usually more enjoyable than fruitlessly attempting to push a telescope's magnification to its theoretical limits. Very high powers are generally best reserved for planetary observations and binary star splitting.

Small aperture telescopes can usually use more power per inch of aperture on any given night than larger telescopes, as they look through a smaller column of air and see less of the turbulence in our atmosphere. While some observers use up to 100x per inch of refractor aperture on Mars and Jupiter, the actual number of minutes they spend observing at such powers is small in relation to the number of hours they spend waiting for the atmosphere to stabilize enough for them to use such very high powers.
75x
Visual Limiting Magnitude:
This is the magnitude (or brightness) of the faintest star that can be seen with a telescope. The larger the number, the fainter the star that can be seen. An approximate formula for determining the visual limiting magnitude of a telescope is 7.5 + 5 log aperture (in cm).

This is the formula that we use with all of the telescopes we carry, so that our published specs will be consistent from aperture to aperture, from manufacturer to manufacturer. Some telescope makers may use other unspecified methods to determine the limiting magnitude, so their published figures may differ from ours.

Keep in mind that this formula does not take into account light loss within the scope, seeing conditions, the observer’s age (visual performance decreases as we get older), the telescope’s age (the reflectivity of telescope mirrors decreases as they get older), etc. The limiting magnitudes specified by manufacturers for their telescopes assume very dark skies, trained observers, and excellent atmospheric transparency – and are therefore rarely obtainable under average observing conditions. The photographic limiting magnitude is always greater than the visual (typically by two magnitudes).

11.9
Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

300mm
Focal Ratio:
This is the ‘speed’ of a telescope’s optics, found by dividing the focal length by the aperture. The smaller the f/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera.

Fast f/4 to f/5 focal ratios are generally best for lower power wide field observing and deep space photography. Slow f/11 to f/15 focal ratios are usually better suited to higher power lunar, planetary, and binary star observing and high power photography. Medium f/6 to f/10 focal ratios work well with either.

An f/5 system can photograph a nebula or other faint extended deep space object in one-fourth the time of an f/10 system, but the image will be only one-half as large. Point sources, such as stars, are recorded based on the aperture, however, rather than the focal ratio – so that the larger the aperture, the fainter the star you can see or photograph, no matter what the focal ratio.

f/4
Resolution:
This is the ability of a telescope to separate closely-spaced binary stars into two distinct objects, measured in seconds of arc. One arc second equals 1/3600th of a degree and is about the width of a 25-cent coin at a distance of three miles! In essence, resolution is a measure of how much detail a telescope can reveal. The resolution values on our website are derived using the Dawes’ limit formula.

Dawes’ limit only applies to point sources of light (stars). Smaller separations can be resolved in extended objects, such as the planets. For example, Cassini’s Division in the rings of Saturn (0.5 arc seconds across), was discovered using a 2.5” telescope – which has a Dawes’ limit of 1.8 arc seconds!

The ability of a telescope to resolve to Dawes’ limit is usually much more affected by seeing conditions, by the difference in brightness between the binary star components, and by the observer’s visual acuity, than it is by the optical quality of the telescope.

1.52 arc seconds
Aperture:
This is the diameter of the light-gathering main mirror or objective lens of a telescope. In general, the larger the aperture, the better the resolution and the fainter the objects you can see.
3"
Weight:
The weight of this product.
4.3 lbs
Telescope Type:
The optical design of a telescope.  Telescope type is classified by three primary optical designs (refractor, reflector, or catadioptric), by sub-designs of these types, or by the task they perform.
Reflector
View Finder:
5 x 24mm
Warranty:
2 years
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Cometron FirstScope 76, 3" tabletop altazimuth reflector

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Our Product #: COM76
Manufacturer Product #: 21023
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The remarkably inexpensive and easy-to-use Celestron Cometron FirstScope 76 Dobsonian-style tabletop reflector is perfect for beginning or casual astronomers who want to experience for themselves a dazzling comet, star cluster, or nebula . . . without spending a fortune.





. . . our 34th year