Responding to your requests, we are pleased to offer the Orion 203mm F/4.9 Reflector Telescope Optical Tube assembly (OTA) for folks who already have an equatorial mount. This optical tube assembly includes parabolic mirror optics, center marked for easy collimation. It has an upgraded 2" Crayford-style focuser (with 1.25" eyepiece adapter), quick-collimation cap, dust cap, and a dovetail base that accommodates any Orion finder scope. Pre-tapped holes in the rear cell allow attachment of an Orion Cooling Accelerator Fan (sold separately). Aperture: 203mm. Focal length: 1000mm (f/4.9). 2" collimatable Crayford-style focuser. The 203mm F/4.9 Reflector Telescope Optical Tube is recommended for visual use or astrophotography. Includes camera adapter. Weighs 16.5 lbs. Tube rings, tube ring mounting plate, finder scope, and telescope eyepieces sold separately.
Limited Warranty against defects in materials or workmanship for one year from date of purchase. This warranty is for the benefit of the original retail purchaser only. For complete warranty details contact us at 800-676-1343.
Please note this product was not designed or intended by the manufacturer for use by a child 12 years of age or younger.
Visit our product support section for instruction manuals and more
Best for viewing
Brighter deep sky
Best for imaging
Highest theoretical magnification
Secondary mirror obstruction
Secondary mirror obstruction by diameter
Secondary mirror obstruction by area
Aluminum & Silicon Dioxide
Optical Tube without Mount
Lunar, planetary & long exposure
Length of optical tube
Weight, optical tube
Additional included accessories
2" focuser with 1 1/4" adapter
In The Box
Orion 203mm F/4.9 Reflector Telescope Optical Tube Assembly
2" - 1.25" telescope eyepiece adapter
Dovetail finder scope base
Starry Night Special Edition astronomy software
Orders received by noon Pacific Time for in-stock item the same business day. Order received after noon will ship the next business day. When an item is not in-stock we will ship it as soon as it becomes available. Typically in-stock items will ship first and backordered items will follow as soon as they are available. You have the option in check out to request that your order ship complete, if you'd prefer.
A per-item shipping charge (in addition to the standard shipping and handling charge) applies to this product due to its size and weight. This charge varies based on the shipping method.
Standard Delivery: $0.00
Standard Delivery to Canada: $60.00
3 Day Delivery: $119.00
2 Day Delivery: $119.00
Next Day Delivery: $136.00
How can I check the collimation of my reflector?
Collimation is the process of adjusting the telescope’s mirrors so they are perfectly aligned with one another. Your telescope’s optics were aligned at the factory, and should not need much adjustment unless the telescope is handled roughly. Mirror alignment is important to ensure the peak performance of your telescope, so it should be checked regularly. Collimation is relatively easy to do and can be done in daylight. To check collimation, remove the eyepiece and look down the focuser drawtube. You should see the secondary mirror centered in the drawtube, as well as the reflection of the primary mirror centered in the secondary mirror, and the reflection of the secondary mirror (and your eye) centered in the reflection of the primary mirror. If anything is off-center, proceed with the collimation procedure. The faster the f/ratio of your telescope, the more critical the collimation accuracy.
Can I center the secondary mirror under the focuser with the aid of the Orion LaserMate?
You can, but it requires marking the center of the telescope’s secondary mirror in the same way the center of the telescope’s primary mirror was marked. This is generally undesirable due to the large area of the supplied collimation targets compared to the total area of the secondary mirror. Since centering the secondary mirror under the focuser is an adjustment that very rarely, if ever, needs to be done, we recommend simply making this adjustment by eye. We’ve tried it both ways and it is just as easy to do it without the Orion LaserMate.
Is the LaserMate Collimator dangerous?
The LaserMate emits laser radiation, so it is important not to shine the beam into your or anyone’s eye. During the collimation procedure, it is also important to avoid direct reflections of the laser beam into your eye. Rather, look only at off-axis reflections to determine the position of the laser spot on the mirrors. It is safe to view the laser when it is reflected off a surface that will diffuse the light, such as the bottom surface of the LaserMate. It is also safe to view the reflection off a mirror surface as long as the beam is not directed into your eye. Because of the potential danger from the laser beam, store your LaserMate out of the reach of children.
How do I align a finder scope?
Before you use the finder scope, it must be precisely aligned with the telescope so they both point to exactly the same spot. Alignment is easiest to do in daylight, rather than at night under the stars. First, insert a low power telescope eyepiece (a 25mm eyepiece will work great) into the telescope’s focuser. Then point the telescope at a discrete object such as the top of a telephone pole or a street sign that is at least a quarter-mile away. Position the telescope so the target object appears in the very center of the field of view when you look into the eyepiece. Now look through the finder scope. Is the object centered on the finder scope’s crosshairs? If not, hopefully it will be visible somewhere in the field of view, so only small turns of the finder scope bracket’s alignment thumb screws will be needed. Otherwise you’ll have to make larger turns to the alignment thumb screws to redirect the aim of the finder scope. Use the alignment thumb screws to center the object on the crosshairs of the finder scope. Then look again into the telescope’s eyepiece and see if it is still centered there too. If it isn’t, repeat the entire process, making sure not to move the telescope while adjusting the alignment of the finder scope. Finder scopes can come out of alignment during transport or when removed from the telescope, so check its alignment before each observing session.
How do I calculate the magnification (power) of a telescope?
To calculate the magnification, or power, of a telescope with an eyepiece, simply divide the focal length of the telescope by the focal length of the eyepiece. Magnification = telescope focal length ÷ eyepiece focal length. For example, the Orion 203mm Newtonian Reflector optical tube, which has a focal length of 1000mm, used in combination with a 25mm eyepiece, yields a power of: 1000 ÷ 25 = 40x.
It is desirable to have a range of telescope eyepieces of different focal lengths to allow viewing over a range of magnifications. It is not uncommon for an observer to own five or more eyepieces. Orion offers many different eyepieces of varying focal lengths.
Every telescope has a theoretical limit of power of about 50x per inch of aperture (i.e. 400x for the Orion 203mm Reflector). Atmospheric conditions will limit the usefullness of magnification and cause views to become blurred. The highest useful magnification of the Orion 203mm Reflector is 300x. Claims of higher power by some telescope manufacturers are a misleading advertising gimmick and should be dismissed. Keep in mind that at higher powers, an image will always be dimmer and less sharp (this is a fundamental law of optics). With every doubling of magnification you lose half the image brightness and three-fourths of the image sharpness. The steadiness of the air (the “seeing”) can also limit how much magnification an image can tolerate. Always start viewing with your lowest-power (longest focal length) eyepiece in the telescope. It’s best to begin observing with the lowest-power eyepiece, because it will typically provide the widest true field of view, which will make finding and centering objects much easier After you have located and centered an object, you can try switching to a higher-power eyepiece to ferret out more detail, if atmospheric conditions permit. If the image you see is not crisp and steady, reduce the magnification by switching to a longer focal length eyepiece. As a general rule, a small but well-resolved image will show more detail and provide a more enjoyable view than a dim and fuzzy, over-magnified image.
What are practical focal lengths to have for eyepieces for my telescope?
To determine what telescope eyepieces you need to get powers in a particular range with your telescope, see our Learning Center article: How to choose Telescope Eyepieces
How do I best view Deep-Sky Objects?
Most deep-sky objects are very faint, so it is important that you find an observing site well away from light pollution. Take plenty of time to let your eyes adjust to the darkness. Don’t expect these objects to appear like the photographs you see in books and magazines; most will look like dim gray “ghosts.” (Our eyes are not sensitive enough to see color in deep-sky objects except in few of the brightest ones.) But as you become more experienced and your observing skills improve, you will be able to coax out more and more intricate details. And definitely use your low-power telescope eyepieces to get a wide field-of view for the largest of the deep-sky objects. For more details, see our learning center article Observing Deep Sky Objects
How do I clean the reflecting mirror of my telescope?
You should not have to clean the telescope’s mirrors very often; normally once every other year or even less often. Covering the telescope with the dust cover when it is not in use will prevent dust from accumulating on the mirrors. Improper cleaning can scratch mirror coatings, so the fewer times you have to clean the mirrors, the better. Small specks of dust or flecks of paint have virtually no effect on the visual performance of the telescope. The large primary mirror and the elliptical secondary mirror of your telescope are front-surface aluminized and over-coated with hard silicon dioxide, which prevents the aluminum from oxidizing. These coatings normally last through many years of use before requiring re-coating. To clean the secondary mirror, first remove it from the telescope. Do this by holding the secondary mirror holder stationary while turning the center Phillips-head screw. Be careful, there is a spring between the secondary mirror holder and the phillips head screw. Be sure that it will not fall into the optical tube and hit the primary mirror. Handle the mirror by its holder; do not touch the mirror surface. Then follow the same procedure described below for cleaning the primary mirror. To clean the primary mirror, carefully remove the mirror cell from the telescope and remove the mirror from the mirror cell. If you have an Orion telescope, instructions to remove the primary mirror are included in your instruction manual. Do not touch the surface of the mirror with your fingers. Lift the mirror carefully by the edges. Set the mirror on top, face up, of a clean soft towel. Fill a clean sink, free of abrasive cleanser, with room-temperature water, a few drops of mild liquid dishwashing soap, and, if possible, a capful of rubbing alcohol. Submerge the mirror (aluminized face up) in the water and let it soak for a few minutes (or hours if it’s a very dirty mirror). Wipe the mirror under water with clean cotton balls, using extremely light pressure and stroking in straight line across the mirror. Use one ball for each wipe across the mirror. Then rinse the mirror under a stream of lukewarm water. Before drying, tip the mirror to a 45 degree angle and pour a bottle of distilled water over the mirror. This will prevent any tap water dissolved solids from remaining on the mirror. Any particles on the surface can be swabbed gently with a series of cotton balls, each used just one time. Dry the mirror in a stream of air (a “blower bulb” works great), or remove any stray drops of water with the corner of a paper towel. Water will run off a clean surface. Cover the mirror surface with tissue, and leave the mirror in a warm area until it is completely dry before replacing in the mirror cell and telescope.
Does my telescope require time to cool down?
As a general rule, telescopes should be allowed to cool down (or warm up) before they are used. If you bring optics from a warm air to cold air (or vice versa) without giving it time to reach thermal equilibrium, your telescope will give you distorted views. Allow your telescope 30 minutes to an hour to reach the temperature of the outdoors before using. When brining your telescope from cool temperatures to warm temperatures, leave any protective caps off until the telescope has warmed-up to prevent condensation. Storing your telescope in the garage or shed where the temperature is closer to the outside temperature will reduce cool down times.
How do I take solar astrophotos?
By attaching a camera body to a telescope, in effect using the scope as a telephoto lens, you can take striking photographs of the Sun. Only attempt this if the telescope is equipped with the proper solar filter. Solar filters are coated to a neutral density of 5, which reduces the light about 100,000 times. Depending on the aperture and focal length of your telescope and “seeing” conditions, you will need to experiment to find the best exposure time for your equipment. We recommend starting with an ISO rating of around 400. At prime focus, start with an exposure of about 1/250 second. Experiment with different shutter speeds. When using higher magnifications, longer exposures will generally be necessary. If you are a beginner in astrophotography and need further information, there are books available that cover this subject completely. Do not be discouraged if your first attempts at solar photography are less than desired. The Sun is very difficult to photograph because of poorer “seeing” conditions caused by unavoidable heat currents associated with daytime viewing. The highest possible resolution for any land-based telescope, regardless of location, is about 1 arc second. Ideal seeing for any location will be available less than 5% of the time. It may be some consolation to consider that your results could equal those at professional observatories, as larger apertures and location have little, if any, advantage. During bad seeing conditions, it may help to “stop down” apertures over 5“ with an off-axis mask.