Orion 9549, 9541, 9909 Care and Maintenance, Do You Wear Eyeglasses?, Image Orientation

Do You Wear Eyeglasses?

If you wear eyeglasses, you may be able to keep them on while you observe. In order to do this, your eyepiece must have enough “eye relief” to allow you to see the entire field of view with glasses on. You can try looking through the eyepiece first with your glasses on and then with them off, to see if the glasses restrict the view to only a portion of the full field. If the glasses do restrict the field of view, you may be able to observe with your glasses off by just refocusing the telescope to your unaided vision.

If your eyes are astigmatic, images will probably appear best with glasses on. This is because a telescope’s focuser can accommo- date for nearsightedness or farsightedness, but not astigmatism. If you have to wear your glasses while observing and cannot see the entire field of view, you may want to purchase additional eyepieces that have longer eye relief.

Short eye relief restricts the field of view for eyeglass wearers.

Long eye relief allows full field of view to be seen with or without eyeglasses.

Do You Wear Eyeglasses?

If you wear eyeglasses, you may be able to keep them on while you observe. In order to do this, your eyepiece must have enough “eye relief” to allow you to see the entire field of view with glasses on. You can try looking through the eye- piece first with your glasses on and then with them off, to see if the glasses restrict the view to only a portion of the full field. If the glasses do restrict the field of view, you may be able to observe with your glasses off by just refocusing the telescope to your unaided vision.

If your eyes are astigmatic, images will probably appear best with glasses on. This is because a telescope’s focuser can accommodate for nearsightedness or farsightedness, but not astigmatism. If you have to wear your glasses while observing and cannot see the entire field of view, you may want to pur- chase additional eyepieces that have longer eye relief.

Image Orientation

Every beginning astronomer has to grapple with the topsy- turvy topic of image orientation in the telescope. Depending on the type of telescope and whether or not it is used in com- bination with a star diagonal, the image you see may be either upside-down, backwards, rotated, or normally oriented.

For most astronomical observing, it makes little difference if an object is seen upside-down or at an otherwise odd angle (after all, there’s no “right side up” in space!). However, for terrestrial viewing you certainly don’t want to see everything upside-down. And when stargazing, it’s hard to compare what you’re seeing to your star chart if the image is inverted or flopped. Let’s sort out the different image orientations seen through different types of telescopes, and see how diagonals figure in the equation.

Refractor and Cassegrain telescopes, when used without a diagonal (which isn’t usually the case), produce an inverted (upside-down) image. The view in Newtonian reflectors is also inverted, or rotated at an angle depending on the eyepiece angle with respect to vertical. Straight-through finder scopes also invert the field of view. If you’re using a star chart, all you

have to do is turn it upside down to match the view through the eyepiece.

Refractor or Cassegrain telescopes used in combination with a standard 90 degree “star diagonal” will provide a right-side- up, but backwards (mirror-reversed), image. Using a star chart is difficult; you have to read it from the back, or do the mental gymnastics to flip the image in the eyepiece left to right to match the chart.

Fortunately, there are special “erect-image” or “correct-image” prism diagonals available that solve the problem, providing a correctly oriented view. Porro prisms (classical erecting prisms) provide correct images while allowing viewing straight through the scope. They do not work with Newtonian reflec- tors, however.

Care and Maintenance

If you give your telescope reasonable care, it will last a life- time. Store it in a clean, dry, dust-free place, safe from rapid temperature changes and humidity. Do not store the telescope outdoors, although storage in a garage or shed is OK. Small components like eyepiece and other accessories should be kept in a protective box or storage case. Keep the dust caps on the front of the scope and on the focuser when it is not in use.

The telescope requires very little mechanical maintenance. The optical tube is made of steel and has a smooth painted finish that is fairly scratch resistant. If a scratch does appear on the tube, it will not harm the telescope. Smudges on the tube can be wiped off with e soft cloth and a household clean- er such as Windex or Formula 409.

Refer to Appendix B for detailed instructions on how to clean the optics of the TableTop.

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