Takahashi Collimation Telescope TCE0100 for RC, Dall Kirkham, Schmidt Cassegrain

Takahashi Collimating Telescope for RC, Cassegrain, Dall-Kirkham Telescopes

With this adjustment telescope, you can collimate your telescope perfectly within a few minutes. Collimation is made using several circles which are consecutively centered. In this process, secondary and primary mirror can easily be identified, so you turn the right screws from the beginning.

The collimating telescope is suitable for all Cassegrain telescopes and their derivatives. Prerequisite is a central mark on the secondary mirror.

Ritchey-Chrétien (RC) telescopes

Dall-Kirkham telescopes

Cassegrain telescopes

Schmidt-Cassegrain telescopes (after putting a central mark on the secondary mirror)

The principle of the Takahashi collimating telescope:

The principle is simple, but ingenious. It is a small telescope with 6x magnification. By using a sliding eyepiece, the single elements in the telescope are consecutively focused. Due to 6x magnification, you can achieve the accuracy which is necessary for a good final result.

The reflex itself is generated by lateral incidence of light and a pierced tilted mirror, similar to a Cheshire. With the diffusing screen, an even illumination is achived, so you can see the rings much easier.

A good achromatic 30 mm objective is placed behind the mirror. Objective and eyepiece provide a good view and ensure quick results.

The telescope has an M36.4 thread at the telescope side. With the two optional adapters (see recommended accessories) you can adapt to 2" and thus attach the collimating telescope directly to the 2" receptacle of your focuser.

In the "Reviews" section, you can find a concise step-by-step tutorial for the collimation of an RC Cassegrain telescope from TS-Optics.

Collimation of an RC telescope with the Takahashi collimating telescope

Preparation and requirements:

For proper use, the following requirements have to be met:

the collimation telescope is already adapted to the 2" focuser, this requires the adapters 4ATDB0 and 5102A1.

the secondary mirror gets a center mark.

if possible, a bright background on which the telescope is directed, and sufficient light for the lateral entry of the Cheshire unit as well a from the front for distinguishing the single planes of the elements.

Adjustment is made with and starting from the existing focuer, as it is used with the telescope and located close to eyepiece or camera. The Takahashi collimation telescope is inserted into the 2" focuser and clamped with the locking screws. It is crucial to ensure that the collimation telescope flushes with the focuser and no tilting occurs, otherways the entire adjustment will become incorrect.

Important: before adjusting, take care that the primary mirror sits firmly in its cell and does not cause tilting. Slightly loosen the lock screw for adjusting the primary mirror.

When looking through the collimation telescope, you can see different rings which in case of a missaligned system will not be symmetrical. Now it´s your job to center these rings to each other.

[If the outer rings are not visible,*] the aperture tube must be unscrewed from the main mirror. Then the outer rings are better visible.

Step 1 - collimating the secondary mirror:

Adjustment always has to start with adjusting the secondary mirror. Concentrate on the small inner rings. The small inner dot represents the entire axis. By tilting the secondary via the three collimation screws at the secondary mirror holder, you can then place the inner rings concentric with the dot. Now the secondary mirror is readily centered.

Step 2 - collimating the primary mirror:

Now focus the outer rings with the collimation telescope. Now place the two larger rings concentrically on top of each other by tilting the primary mirror. Depending on telescope aperture, the larger ring might now overlap the smaller one. When you have succeeded in doing so, the RC is readily adjusted.

The final check with an artificial or natural star:

The star will already be almost perfect. You can perform minimal readjustments by carefolly tilting the primary mirror.

What to do in case of astigmatism on the axis:

This aberration is feared with RCs. It mostly results from a lateral offset of the primary mirror. In this case check if the primary mirror is well seated in the cell. For RC telescopes from TS-Optics, this is always checked prior to shipping. If it is not the case, then center the primary mirror and start with collimation from the beginning.

If the astigmatism is only minimal, you can gently adjust the primary mirror.For this, use the collimation screw on which the major axis of the ellipse of a defocused star is pointing at. The star now should move in exactly this axis if you adjust the primary mirror. It the direction is correct, the ellipse slowly turns into a circle. But don´t forget to adjust the secondary mirror again (step 1).

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