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Thank
you for choosing Celestron. Welcome to the support page
for the NexStar 80 GTL telescope.
Celestron's Frequently
Asked Questions
NexStar 80GTL Telescope Questions
Answers
Q: Why do planets appear as small dots, even with my 10mm eyepiece?
A: You need to use a higher power eyepiece. Remember that the smaller the focal length of the eyepiece you use, the higher the magnification you will see in the scope. The NexStar 80 GTL comes with a 25mm eyepiece and a 10mm eyepiece, which give you 36 and 90 magnification respectively. At 90 magnification Jupiter and Saturn are easily resolvable, however Mars may appear as a small bright disk.
To get better planetary images, you need to use an optional eyepiece of a shorter focal length. This scope is capable of using an eyepiece down to 5mm which will give you 180 magnification and will show a larger disk than what you are seeing now. It will still be a small disk, but you will be able to see more detail than with the provided eyepieces.
For more on this topic refer to the section on calculating magnification on p.22 of your user’s manual.
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| Mars through an ocular (eyepiece) equal to 200 X |
Mars through an ocular (eyepiece) equal to 90 X |
Q: How can I get more power in my telescope?
A: You can get different magnification in your scope by simply changing eyepieces. Remember; Power = Focal Length of optical tube (900mm) divided by Focal Length of eyepiece.
Thus a 25mm eyepiece will yield 36 power (900/25 = 36); a 10mm will yield 90 power, and so on up to a maximum power of 180 which is achieved with a 5mm eyepiece.
Another option for increasing your magnification is to use a Barlow lens. A Barlow lens can be used with your existing eyepiece and it will double the magnification of any existing eyepiece.
For more information on eyepieces and accessories please refer to your accessory sheet that came with your telescope.
Q: Why does my scope move well past the alignment stars when I attempt to use Auto-Align?
A: Having the wrong model selected in the hand control can change the gear ratios the scope uses to calculate the correct position of objects in the sky. To correct this, go into the main menu using button #3 and go into the Utilities menu. Choose “Select Model” and select 80mm off the list. It will ask you to recycle the power. Simply unplug the power supply and wait a few seconds before plugging it back in. This should take care of any pointing issues.
For more on this topic refer to the section on Hand Control Operation on p.13 of your user’s manual.
Q: When I try to align the scope, why does my scope point down to the ground?
A: This sounds like the tube ring was installed upside down. This is an easy fix. Look for the black knob on the large black ring that holds the telescope in place. This knob is most likely located on the bottom of the tube ring with the hinge on top. This is exactly 180 degrees reversed.
Holding the tube, remove the black thumbscrew and remove the tube from the ring. Now grab the ring and rotate it 180 degrees so the hinge is at the bottom and the black screw is at the top. Replace the tube in the ring the same way you removed it and tighten the silver thumbscrew. This should take care if it.
For more on this topic refer to the section on Assembling the NexStar on p.6-7 of your user’s manual.
Q: I have a star or planet centered in my Star Pointer finderscope, but I can't see anything in the eyepiece. What am I doing wrong?
A: It sounds as if the Star Pointer is not aligned to the telescope’s optics. This must be done once when the scope is first set up.
Take the scope out in the daytime and point the scope down the street towards the top of a telephone pole, street sign, or license plate on a car (or any SMALL target that’s easily recognizable). Using your lowest power eyepiece (the one with the highest focal length number printed on it), look into the eyepiece of the main scope and center it on the target.
Now look through the Star Pointer and the first thing you’ll notice is that the red dot is most likely not aimed at the same target. Now adjust the small round thumbscrews on the star pointer to adjust the elevation (up/down) and azimuth (left/right) of the red dot until it lies on top of the same object you are viewing through the eyepiece. Once this is done, you are ready to view.
Now anything you point the red dot star pointer at will ALSO appear in your eyepiece. The Star Pointer should remain in alignment unless the finder is bumped into something, like when you move the scope in and out of the house. If this happens, simply realign it. This can also be done at night using a distant streetlight or a star.
For more on this topic refer to the section on Star Pointer Operation on p.9 of your user’s manual.
Q: Why does the front of the telescope droop downward whenever I point it close to level?
A: This scope comes with a slip clutch in the altitude axis. If the tube is placed in the tube ring too far forward, the scope’s weight will overcome the tension of the clutch and the scope will slip downward. Your scope will have an easy time moving downward, but will not likely be able to move upward without the motor slipping. This can throw off your alignment. To eliminate this, you need to balance the optical tube in the tube mounting ring. Simply loosen the black thumbscrew located at the top of the tube ring. Now slide the tube either forward or backwards until the tube “feels balanced” and tighten the black thumbscrew down. To make balancing the tube easier, the NexStar 80GTL has a sticker on the tube that has a black line indicating the approximate balance point.
For more on this topic refer to the section on balancing the Telescope Tube on p.7 of your user’s manual.
Q: Why can’t my telescope point straight upward?
A: Due to the design of the fork assembly and the balance point of the tube, your scope will be unable to point directly to the zenith (straight up). The electronics have user defined restrictions in the hand control that limit the movement of the scope to about 70 degrees in elevation. These restrictions are in place to prevent the scope from hitting the tripod during movement. This means that objects above 70 degrees in elevation can not be viewed. This is only a temporary problem however because the Earth is rotating at 15 degrees an hour. This means if an object is too high in the sky to be viewed, it will only be out of range for a short period of time.
For more on this topic refer to the section on Filter Limits on p.18 and Slew Limits on p.20 of your user’s manual.
Q: Why are all nine planets not in the “planet” database?
A: This telescope is equipped with electronic filters that prevent you from being able to select objects that are below your visible horizon or outside of the scope’s range of slewing. It does this by removing any objects from the catalogs that are not currently over the horizon at that moment. This way you do not waste your time and battery life by slewing to objects that are below the horizon or too close to the zenith (straight overhead).
As soon as these planets rise over the eastern horizon, their names will reappear in the planet catalog (assuming you have entered the correct date, time, and location in the hand control). If a planet sets behind the western horizon, its name will be removed from the displayed list.
For more on this topic refer to the section on Filter Limits on p.18 of your user’s manual.
Q: I use a compass to align my scope north, but my telescope will still not place an alignment star within the finderscope’s field of view. Why not?
A: The telescope’s computer needs a single reference point in space in order to locate the approximate positions of the alignment stars. This scope uses true north and level to define this point. Unfortunately, a compass reads magnetic north and not true north. The lines of magnetic flux in the Earth’s magnetic field do not run in straight lines, resulting in variances between true north and magnetic north that can exceed 20 degrees.
The best way to find true north is to look for Polaris, the North Star. It lies less than a degree away from true north and is easily found by using the pointer stars in the big dipper. When aligning your telescope, you place Polaris in the center of the Star Pointer, then lower the tube so that it is level and then start the alignment procedure.
For more on this topic refer to the section on Alignment on p.13 of your user’s manual.
Q: My scope fails to put objects in the eyepiece when I give it a go to command using the hand control. What can be done to improve this pointing accuracy problem?
A: Answer 1: If by pointing accuracy, you are referring to the accuracy in the scopes ability in initially finding the alignment stars, make sure that you have positioned the scope towards true north, not magnetic north. True north is easily found by locating Polaris, also known as the North Star. Also check your hand controller to make sure that you have the correct model, NexStar 80, selected. This can be done on the hand control by going to menu (button 3)/utilities/select model.
For more on this topic refer to the section on Alignment on p.13-14 of your user’s manual.
Answer 2: If the problem is inaccurate pointing accuracy AFTER you complete your alignment (you have already received the “alignment successful” message) make sure that:
- Your tripod is level
- You have accurately centered the alignment stars in your eyepiece.
- When centering those alignment stars in the eyepiece, always FINISH by using the up and right arrow keys.
- You are using a proper power supply.
For more information on this topic refer to the section on Alignment on p. 13-14 of your user’s manual.
Q: What can I expect to see in my telescope?
A: Your scope has a 3.1 inch (80mm) aperture. You should have no problem seeing most of the planets (Jupiter and Saturn especially) and great views of our moon. You may be able to see some fainter nebula and star clusters depending on seeing conditions, etc. Using the included solar filter, you should be able to see details of the Sun’s surface including sunspots.
The ability to see detail in a telescope is largely dependent on aperture; specifically, the more the better. Thus, a 6 inch scope will have 4 times the light gathering power of a 3 inch scope. This helps those faint objects like galaxies and nebula to appear more brightly in your eyepiece. Some objects are so faint that they just can not be seen at all in a 3 inch scope. Your 80 GTL is a great beginning scope, and it is certainly portable, but for the more advanced astronomer remember that the larger the aperture of your telescope, the better the results.
For more on this topic refer to the section on General Observing Hints on p. 23 and Celestial Observing on p. 24-26 of your user’s manual.
Q: Can my telescope be used for terrestrial viewing?
A: Yes. But remember: Terrestrial viewing is best done between 15-60 magnification. If you exceed 60x magnification the atmospheric interference from the air, especially on a hot day, can drastically distort your image. Early mornings are best for high power viewing because the air temperature is more constant. For more information on this topic refer to the section on Terrestrial (Land) Viewing on p. 25 of your user’s manual.
Q: How do I get an erect image in my eyepiece?
A: You must use the Erect Image Prism (supplied with the scope). Using the eyepiece straight through the scope without the diagonal can be done but it will yield an upside down image.
For more on this topic refer to the section on Image Orientation on p.22 of your user’s manual.
Q: Can I use my telescope for photography?
A: Yes. Your telescope has a built in camera adapter. Simply remove the erect image diagonal and you will see 42mm external threads at the rear of the telescope. Those are called T-threads. Now all you need is a T-ring to attach your SLR camera. Since each brand of camera has its own specific thread size, you need to get the proper T-ring adapter. Thus Canon has its T-rings (two of them); Nikon has its own T-rings; Minolta has their own specific rings, and so on.
For more on this topic refer to the accessories section of the Celestron Web Site on choosing the appropriate T-ring for your SLR camera.
http://www.celestron.com/prod_pgs/accessories/photo_visual_accessories.htm
Don’t forget: when adding a camera you are adding weight. Make sure that you rebalance your telescope once you have added the camera.
For more on this topic refer to the section on balancing your telescope on p. 7 of your manual.
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