Very simple, precise and quick to use - though you may require another hand for the bigger template and larger mirrors. As an aside, the previous centre ring on my skywatcher mirror was 2mm off, which F5 is not accurate enought 2.
Products included in the price:. Catseye 15" Template Select: Choose: Triangle. Average Rating 3 Reviews : Write a Review and share your opinions!
Wow what a difference, I can now use my 4mm eyepice on my scope. Saturday, 27 February Paul. Precise and easy to use template!
Monday, 14 September Daniel. Catseye Centring Template. Friday, 21 February Jake. Related Products. Illumination is accomplished by light directed at the primary mirror which is reflected back to the reflective ring via the diagonal. A Cheshire device is used in conjunction with a "reference" center spot on the primary mirror to adjust the primary tilt.
The CATSEYE TM System utilizes a special highly reflective triangle center spot sized to just fit inside the image of the reflective ring; the points of the triangle are aligned with the primary adjustment screws. There is a round, flat mirror on the backside of the peephole inside the tube with the mirrored surface facing toward the open end of the tool. A small amount of the mirrored surface has been removed at the center of the mirror to allow sight through the peephole.
It helps to move the focuser in and out until all three circles are similar in size to enable better visualization of concentricity. This will only have to be done once, though in initial collimation you may have to repeat it a couple times after doing the next step, so take your time to make it right. If moving it sideways to center its outline in the sight tube makes the secondary appear non-round or oval, rotate the secondary on its center-bolt until it appears round again.
When you are done, the secondary will appear concentric to the sight tube, and round in outline. See the following diagram of the appearance of a properly positioned secondary in a collimated scope as seen through the sight tube. This is what you will achieve.
Here is the same view with a slightly smaller secondary in the view to emphasize the lack of concentricity of the secondary mirror reflection shadow's outline to the other images. The laser must itself be collimated or using it will misalign the scope. Many low-cost lasers come out of the box uncollimated. It is primarily for this reason I prefer the sight tube. Insert the sight tube and fasten the setscrew tight. You cannot successfully collimate without one.
A transparent mirror center-spotting template such as the ones available from Catseye for all mirror sizes and FarPoint for mirrors under 15" allows a home user to perfectly position the center dot to less than 0. This may move the round image of the outline of the secondary out of concentricity with the inside diameter of the sight tube.
If so, repeat Step A and then Step B again. Each iteration brings the secondary closer to exact alignment. The centering of the secondary mirror in the focuser is only to provide even illumination of the image all the way around the edge of the field of view—less important than correctly adjusting the optical reflection from the secondary mirror with regard to the focuser axis.
When the telescope's primary is collimated, this distant reflection of the crosshairs will be hidden behind the near-field crosshairs. This distant reflection of the underside of the crosshairs is removed for simplicity in the BEFORE image that follows. Some people have trouble focusing on the center mark and the crosshairs at the same time. It helps to use glasses in that case, or back the eye up far enough to allow both to be in focus. It should be noted that this is adjusting the secondary to the focuser axis, but it does not adjust either rotation or centering of the secondary relative to the focuser.
Since adjusting the tilt may move the secondary off-center relative to the focuser, you may need to check again with the Sight Tube. This step essentially aligns the secondary to the focuser axis, so that moving the focuser in and out as in focusing will make no difference in collimation. With Uni-Directional Offset, the Optical axis will be ever-so-slightly tilted toward the focuser.
This will make literally no difference at the eyepiece, but MAY make a difference to certain brands of digital setting circles DSC used in certain conditions. Note this offset is very small, and is less deleterious to the accuracy of a DSC than inaccurate centering of the alignment stars.
The advantage of Uni-Directional Offset is that the secondary remains centered in the tube and appears centered under the focuser. Both conditions can be achieved at the same time, and easily. Bi-directional offset requires calculations. What follows is an illustration with 2 different versions of Full Offset wherein the secondary is also offset away from the centerline of the optical tube they are two different ways of achieving "Classical" Offset.
Note that Uni-Directional Offset, which is the technique described in this article, does not require the mechanical offsetting of the secondary that shows in the illustration, yet results in the same full offset relative to the optical centerline when the scope is collimated.
The left illustration shows the entire secondary and holder offset bi-directionally, while the right illustration shows the "Classical" way of doing it, wherein only the mirror is offset. Since it is simpler to accomplish, it is Uni-Directional Offset which has been described in the collimation procedures in this article. This is here primarily to show that there is more than one way to accomplish Bi-directional Offset collimation.
Note that in Bi-Directional offsetting of the secondary mirror it is dropped toward the primary mirror and moved slightly away from the focuser. This keeps the mechanical center axis of the tube coincident with the optical axis of the telescope. The secondary will no longer be centered in the tube from side-to-side. But it is much easier to accomplish for the user because the secondary mirror stays centered in the tube. A Cheshire eyepiece is either a cylindrical tool with a hole in the side of it and an internal degree mirror to reflect light from the sky down onto the primary mirror and back or an even-simpler tool with a bright ring on the bottom and a simple peep hole on the other end pictured.
Be careful when you insert a degree Cheshire like the Tectron or most combination tools on the market the type with an open window on the side that you do not cover the side hole with the bill of a cap so the 45 degree surface can reflect the bright light of the ceiling or sky; for the simpler bright ring type pictured , the tool should be fully inserted. What this tool provides, when viewed through, is a reflected bright ring with a dark center.
Use the collimation screws on the Primary mirror to move the reflected image of the center marker into the dark center of the bright ring of reflected light. It may be necessary, if a lot of movement is required, to repeat Step B for the Secondary mirror, and then repeat Step C this is usually only necessary when a scope is assembled from components or a major shift in primary alignment follows disassembly of a mirror cell for the replacement of springs.
In a properly collimated telescope both secondary and primary alignment will agree at the same time. If a combination tool is used, the crosshairs, center dot, and dark center and reflected crosshairs will all line up at the same time. If a barlowed laser is used, the reflected red beam will have a dark shadow of the reflected center marker that you will center on the open hole at the bottom of the Barlow. This alignment is just as accurate as a Cheshire, and some would argue less intrinsically plagued by parallax—presuming, of course, that you can even see the bottom of the Barlow from the bottom of the focuser.
I will not describe the Barlowed Laser Technique, here, even though it is as accurate as a Cheshire used properly because you cannot see the image on the bottom of the Barlow on-axis and because a typical Barlow does not enter the focuser deeply enough to have its bottom visible except in large scopes with low-profile focusers. Addendum: Devices now exist to allow the bottom of the Barlow to be seen from either the front of the scope or the bottom of the scope easily, inside or outside the focuser drawtube.
The only possible downside to these would be possible registration errors cause by a multiplicity of devices inserted in the focuser, each with its own possible registration error.
If a perfectly collimated single point laser is used, the return beam will accurately track the outward beam to its source. However, a single beam laser can return its beam to the source with errors in mirror placements and tilt, not to mention the difficulty of the accuracy assessment, so if a laser is used, the Barlowed laser technique is strongly recommended for primary mirror alignment. This tool is so sensitive to misalignment that simple mechanical flexures will be visible i.
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