Orion 52598, Instruction Manual

10

Let Your Eyes Dark-Adapt 

Don’t expect to go from a lighted house into the darkness of the 
outdoors at night and immediately see faint nebulas, galaxies, 
and star clusters—or even very many stars, for that matter. Your 
eyes take about 30 minutes to reach perhaps 80% of their full 
dark-adapted sensitivity. As your eyes become dark-adapted, 
more stars will glimmer into view and you’ll be able to see fainter 
details in objects you view in your telescope. 
To see what you’re doing in the darkness, use a red-filtered 
flashlight rather than a white light. Red light does not spoil your 
eyes’ dark adaptation like white light does. A flashlight with a red 
LED light is ideal. Beware, too, that nearby porch, streetlights, 
and car headlights will ruin your night vision. 

“Seeing” and Transparency 

Atmospheric conditions vary significantly from night to night. 
“Seeing” refers to the steadiness of the Earth’s atmosphere at a 
given time. In conditions of poor seeing, atmospheric turbulence 
causes objects viewed through the telescope to “boil.” If you look 
up at the sky and stars are twinkling noticeably, the seeing is 
poor and you will be limited to viewing at lower magnifications. At 
higher magnifications, images will not focus clearly. Fine details 
on the planets and Moon will likely not be visible. 
In conditions of good seeing, star twinkling is minimal and 
images appear steady in the eyepiece. Seeing is best overhead, 
worst at the horizon. Also, seeing generally gets better after 
midnight, when much of the heat absorbed by the Earth during 
the day has radiated off into space. 
Especially important for observing faint objects is good “trans-
parency” - air free of moisture, smoke, and dust. All tend to scat-
ter light, which reduces an object’s brightness. Transparency is 
judged by the magnitude of the faintest stars you can see with 
the unaided eye (6th magnitude or fainter is desirable). If you 
cannot see stars of magnitude 3.5 or dimmer then conditions 
are poor. Magnitude is a measure of how bright a star is - the 
brighter a star is, the lower its magnitude will be. A good star to 
remember for this is Megrez (mag. 3.4), which is the star in the 
“Big Dipper” connecting the handle to the “dipper”. If you cannot 
see Megrez, then you have fog, haze, clouds, smog, or other 
conditions that are hindering your viewing. (See 

Figure 26

.)

Tracking Celestial Objects 

The Earth is constantly rotating about its polar axis, complet-
ing one full rotation every 24 hours; this is what defines a “day”. 
We do not feel the Earth rotating, but we see it at night from 
the apparent movement of stars from east to west. When you 
observe any astronomical object, you are watching a moving 
target. This means the telescope’s position must be continu-
ously adjusted over time to keep an object in the field of view. 
This is easy to do with the SkyScanner BL because of its smooth 
motions on both axes. As the object moves off towards the edge 
of the field of view, just lightly nudge or tug the telescope to 
re-center it. Objects appear to move across the field of view 
faster at higher magnifications. This is because the field of view 
becomes narrower.

Eyepiece Selection 

By using eyepieces of different focal lengths, it is possible to 
attain many magnifications or powers with the SkyScanner 

BL. Your telescope comes with two 1.25" eyepieces: one with 
25mm focal length and one with 10mm focal length. To calculate 
the magnification of a telescope-eyepiece combination, simply 
divide the focal length of the telescope by the focal length of 
the eyepiece:

Telescope Focal Length (mm) 

= Magnification

Eyepiece Focal Length (mm)

For example, the SkyScanner BL 102mm, which has a focal 
length of 640mm, used in combination with the 25mm Kellner 
eyepiece, yields a magnification of 26x: 

640mm 

= 26mm

25mm

The 10mm Plossl eyepiece included with the SkyScanner BL 
102mm produces a magnification of 64x.
For the SkyScanner BL 135mm, the 25mm eyepiece yields a 
magnification of 44x, while the 10mm Plossl eyepiece magni-
fies 110x. Other 1.25" telescope eyepieces can be purchased 
to achieve higher or lower powers. It is quite common for an 
observer to own five or more eyepieces to access a wide range 
of magnifications. 
Whatever you choose to view, always start by inserting your 
lowest-power (longest focal length) eyepiece to locate and 
center the object (in this case the 25mm). Low magnification 
yields a wider field of view, which shows a larger area of sky 
in the eyepiece. This makes finding and centering an object 
much easier. Trying to find and center objects with a high power 
eyepiece, which has a narrower field of view, is like trying to find 
a needle in a haystack! Once you’ve centered the object in the 
eyepiece with the 25mm, you can switch to a higher magnifica-
tion (shorter focal length) eyepiece, if you wish. 
The best rule of thumb with eyepiece selection is to start with a 
low power eyepiece, and then work your way up in magnifica-
tion. If the object looks bet¬ter, try an even higher magnification 
eyepiece. If the object looks worse, then back off the magnifica-
tion a little by using a lower-power eyepiece. 

Magnification Limits 

Every telescope has a useful magnification limit of about 2x per 
millimeter of aperture. This comes to 204x for the SkyScanner 
BL 102mm, and 270x for the SkyScanner BL 135mm. Some 
telescope manufacturers will use misleading claims of excess 
magnification, such as “See distant galaxies at 640X!” While 
such magnifications are technically possible, the actual image 
at that magnification would be an indistinct blur. Low and moder-
ate magnifications are what give the best views. A small, but 
bright and detailed image is always better than a dim, unclear, 
over-magnified one.

Using the MoonMap 260 

Orion’s MoonMap 260 is a great observing aid to use when view-
ing the Moon with your SkyScanner BL. With it you will be able 
to identify a myriad of lunar features. Because the view in the 
SkyScanner BL is rotated from upright, you may find it useful 
to rotate the MoonMap so the image on the map matches what 
you see in the telescope eyepiece. Concentrate each evening 
on the “terminator”, where the illuminated portion of the lunar