Astromania 1.25Inch Metal Collimating Cheshire Eyepiece Without Laser for Newtonian Reflector Telescope - Short Version
Collimation is the process by which an instrument’s
optical components are brought into precise alignment with its optical axis
and mechanical axis. In other words, all the mirrors and/or lenses should be
centered and angled so that light entering the telescope forms a sharp image
precisely in the center of the eyepiece. If the optics are not properly
aligned, stars will appear not as pinpoints as they should, but rather as
flared, teardrop-shaped “comets” or “sea gulls.” Purpose of the Collimating
Eyepiece Aligning the mirrors seems easy enough, in theory, but in practice it
can be difficult without the proper tools. A common way of collimating—the
“quick and dirty” method—is to simply remove the eyepiece and look down the
focuser tube to center the mirror reflections. The accuracy of this method,
however, is not reliable. For one thing, there is no way to know whether you
are looking straight down the focuser tube; your line of sight could be off by
a degree or two. Another problem is knowing when the reflections of the
mirrors are exactly centered. Just “eyeballing it” isn’t precise enough; the
reflections may appear to be centered when in fact they are not. The
Collimating Eyepiece will take care of both of these problems, allowing you to
achieve precise collimation without “guessing,” and thus improve your
telescope’s performance. The Collimating Eyepiece is a combination of a “sight
tube” and a “Cheshire eyepiece.” The sight tube’s narrow field of view and
crosshairs provide a reference for centering the optical elements during the
collimation process. A Cheshire eyepiece has a polished flat set in the barrel
at a 45° angle, which directs light entering from a cutout in the side of the
barrel down into the optical path. The Cheshire allows quick and easy
collimation of the primary mirror, assuming the mirror has been marked with a
spot exactly in its center. Using the Collimating Eyepiece Collimation can be
performed in daylight, when it is easier to see what you’re doing. However,
never point the telescope or the cutout side of the Collimating Eyepiece at,
or anywhere near, the Sun, or serious and instant eye damage could result!
Insert the Collimating Eyepiece directly into the 1.25" focuser. When using a
2" focuser, place the Collimating Eyepiece into a 1.25" adapter. If you use a
star diagonal with your telescope, as is common for Schmidt-Cassegrain
telescopes, remove it before inserting the Collimating Eyepiece. The eyepiece
should be inserted to a depth such that the bottom edge of the eyepiece tube
appears slightly wider than the outer edge of the secondary mirror when you
look through the sight hole. Rotate the eyepiece so that the cutout side is
directed toward any available external light. Make sure there is adequate
light in the room or outside so that when you look through the sight hole, you
can see the edges of the secondary mirror clearly. Tighten the thumbscrew on
the focuser tube to secure the Collimating Eyepiece in place. Now, you are
ready to proceed with collimation. Collimation of Refracting Telescopes If you
use the eyepiece for checking the collimation of a refracting (lens)
telescope, then you will see as many reflections as there are lenses in the
telescope. If all the reflections are round and centred, then your telescope
is well collimated. Short Metal Tube with Crosshairs The Cheshire collimation
eyepiece is simple but absolutely effective. With practice, you will be able
to collimate your Newtonian telescope in just a few minutes - especially if
simply finely collimating your telescope for optimal imaging. The Cheshire
eyepiece consists of a short metal tube and a 45° base. The reticule gives you
the orientation required for the optical axis. Collimation of Different
Telescope Types Good collimation is particularly critical for “faster”
Newtonians, those with f-ratios of f/6 or lower. Once the collimation is set,
it will hold if care is taken in transporting and handling the optical tube.
However, any sharp jolts can knock the mirrors out of alignment, as can
jostling of the scope in the trunk of a car or temperature changes over a
period of time. Fortunately, these telescopes are equipped with adjustment
screws that permit easy recollimation. Testing Your Telescope’s Collimation
Just point it at a bright star and slowly rack the image out of focus by with
the focusing knob. If the telescope is correctly collimated, the expanding
disk should be a perfect circle. If it is unsymmetrical, the scope is out of
collimation. In reflectors and Schmidt-Cassegrains, the dark shadow cast by
the secondary mirror should appear in the very center of the out-offocus
circle. If the “hole” appears off-center, the telescope is out of collimation.
Care and Maintenance Since there are no lenses in the Collimating Eyepiece,
care and maintenance is minimal. It is a good idea to remove any obvious dirt
on the inside or outside of the eyepiece so that the dirt does not get into
the telescope tube during the collimation process. To clean the eyepiece, use
a blower bulb or a moist cotton swab to remove dirt from inside the barrel,
and simply wipe the outside with a damp cloth. Make sure not to disturb the
crosshairs, as bending or breaking may result. Read more
- Fits in 1.25" focusers and easy to use;simply cap the telescope, remove the diagonal, and place the eyepiece directly in the focuser.
- For aligning optics of Newtonian reflectors, Dobsonian reflectors, and Schmidt-Cassegrain Telescopes (SCTs).
- The short collimator for mirror (reflector) telescopes has a 45 degree plate for easier visual accuracy.
- Item was made by aluminum with crosshair at the bottom allow quick and precise centering of the optics.
- This collimation eyepiece can be used for precisely collimating the Newtonian and Schmidt-Cassegrain reflector telescopes for better image quality.
- Product Dimensions: 6 x 1.3 x 1.3 inches
- Item Weight: 3.04 ounces
- Shipping Weight: 3.2 ounces
- Item model number: SKU_AM_MCES1
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Filed under: Eyepieces & Accessories