Takahashi Collimation Telescope for RC, DK, SCT and Cassegrain telescope collimation
Takahashi Collimation Telescope can be used to collimate RC, DK, SCT and other Cassegrain telescopes using nothing but some light. Let see how it all works out.
The collimation telescope is actually a
typical collimation tool that connects to telescope focuser. It was created for Takahashi Mewlons but can be used with Dall Kirkham, RC, SCT and other Cassegrain telescopes if the secondary mirror has a center point mark.
The tool shows an image of rings which become symmetrical when collimated. To make the rings visible the telescope must be looking at something bright (wall, sky and alike). Some light must also pass through a plastic
window on the side. The tool is intended for visual use and ends up with built in eyepiece.
The tube of the collimator can be extended to focus the rings image. It's friction based with no locking so it's best to orientate the scope more horizontally.
To connect the collimation telescope to a 2" focuser you will need two adapters:
Takahashi Adapter from 36.4 mm to 43 mm and
Takahashi Adapter from 2" to M43x1 thread. In Europe that's around 270 EUR for the telescope and 45 - 50 EUR for adapters.
Put the device in the focuser and double check if it's locked properly and not tilted in any way. Next look through the device. You should see a bright ring/dot in the center and weaker around it, potentially off-center. If the image isn't in focus move the tube to focus it. This is the secondary mirror. Correct it screws so that the second ring becomes centered:
The inner rings will be within another ring that will represent the primary mirror. Correct it screws so that the ring is symmetrical:
After that the telescope is collimated, although it may require final touches using defocused star image and a camera.
There is no easy way to connect a camera to the device. You can use a guide/planetary camera with C/CS lens and use a eyepiece projection adapter that would be compatible with given camera (like tripod thread on ASI cameras). If you want to use a phone for which there is plenty of adapters then it would be best to have an option to view it screen remotely so that you see changes as you collimate the secondary mirror. If not you will have to go back and forth.
In my case I used a small and lightweight PGR Chameleon camera with a C/CS lens and taped everything to the device. The lens allowed to center the camera on the image from the collimator quite easily.
The collimation process is easy to do and it's quick. The only requirement is having that mark on the secondary mirror - not every telescope will have it. Depending on your location the availability of this device may be limited and the price isn't low either.