![]() Select a star that’s around 2nd magnitude, and centre it in your scope. It can be performed in the dark and requires no tools - only a clear night sky. The method outlined here is essentially a star test, but with a twist. Luckily, there’s a way of achieving optical alignment that bypasses these considerations. In addition collimation accuracy, depends to some extent on how precisely the tools were made, and how carefully the centre mark was positioned. That’s fine for Newtonian reflectors, but not for SCTs and Maks. For instance, most collimation devices depend on the centre of the primary mirror being marked in some way. But in spite of their utility and usefulness, tools like these do have their shortcomings. Most of the time when we need to align the optics in our scope, we reach for devices such as a Cheshire eyepiece or laser collimator. Here’s a method that’s simple and doesn’t require tools or even a centre-dotted primary mirror. Most telescope users know that the only way to get every last drop of performance from a reflector telescope is to ensure that the optics are in good collimation. Luckily, achieving this goal doesn’t have to be difficult. These thumbscrews let you collimate without tools, so you can easily make adjustments to the secondary without any concerns of damaging your SCT’s optics.For optimum performance, precisely aligned optics are a must. ![]() The most popular is a set of knurled knobs that replaces the hex head screws. Several aftermarket solutions are available for this problem. What may not be so easy is the inconvenience and anxiety of using a small, metal Allen wrench or Phillips screwdriver in the dark just above the vulnerable surface of your telescope's corrector plate to turn the three screws for collimation. For Fastar-equipped SCTs, turn the triangular cover plate either clockwise or counterclockwise to reveal the collimation screws. Some optical tubes hide the screws under a cover that you can easily pry off with a fingernail. Celestron SCTs use 3 small Phillips or hex head screws for adjustment. For SCTs, it’s done by small adjustments to the tilt and position of the secondary mirror in its cell. Precise collimation is essential to good performance for any Schmidt-Cassegrain telescope. Here are a few links on SCT collimation and the Airy disk. You will use these rings to collimate your telescope just as you did in the previous steps. At high magnification, a star will not look like a point, but like a small central disk surrounded by concentric rings (called the Airy Disk). Your telescope must be the same temperature as the ambient air. You will want to do this on an extremely calm night and use a star at or near the zenith. When everything looks concentric and uniform, it’s now time to do an in-focus collimation. Again defocus the star just a little bit and make small adjustments with the collimation screws. Switch to a high-power eyepiece–about a 2.5 mm focal length is recommended. Out-of-collimation SCT showing star going from inside to outside of focus.Ģ. Turn the screws by only 1/6 to 1/8 turn adjustments, Each time you make an adjustment the star will move in the field of view, and you’ll need to re-center the star to check if the scope is in collimation. Remove the logo cap over the secondary housing by gently prying with your fingernail. To center this spot you will need to adjust the collimation screws located on the secondary mirror housing. This dark spot will not be in the center of the defocused star if the scope is out of collimation. Next, defocus the star until you can see a center dark spot (this is the secondary mirror shadow). Using a medium-powered eyepiece, center a medium-brightness star in the field of view. This initial step will get you in the ballpark for more accurate collimation later on. Start with a rough out-of-focus collimation. Choose only nights with superior seeing for collimation.ġ. This makes the air act like a weak lens that interferes with the light from a planet or a star by defocusing it. Heat waves and high-altitude winds move air around and cause differing temperatures of air to mix. Seeing (the steadiness of the atmosphere) also affects your collimating ability. You may need to keep it in an unheated room over a period of a few days. If there is a significant temperature difference between outside air and the scope’s storage area, you’ll need to wait at least an hour, maybe several hours for the scope to reach the ambient temperature. ![]() There are three stages to a really good collimation using the stars or a star-like source (such as a solar reflection off a distant ball bearing or Christmas tree ornament).īefore attempting fine collimation, especially in-focus collimation, always let the scope reach the temperature of the outside or ambient air. Collimation of a SCT is critical to getting the sharpest images possible, especially when viewing planets at high magnification.
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