Mewlon 300

This is my Takahashi Mewlon 300, mounted on my Astro-Physics 1200 mount.

Below are some pictures I took when I had to clean the primary mirror in July 2011. For this the tube with secondary has to be taken off so that the mirror is accessible.

After cleaning the mirror and remounting the instrument, collimation remained almost spot-on, only a small tweak to the secondary collimation was needed.

One month after cleaning, unexpectedly the CDK conversion kit arrived. Below is the Takahashi Mewlon 300 CDK conversion kit, comprising of a new baffle with correcting optics, a new back-end/eyepiece adapter and the CDK RD-CR 0.73x reducer for this system.

The tele-extender for this system is available as well, but I didn't purchase it.

Below are a few images taken while I did the conversion on 18 September 2011. Left is the system with the original baffle, center is the original baffle side-by-side to the CDK conversion baffle, at right the new baffle is installed. Conversion is straight forward: inscrew the old baffle and replace it with the new CDK baffle. Caution: do not remove the conical focuser adapter on the back when doing this swap, otherwise you wiill not be able to screw in the new baffle. After the conversion is done and the telescope assembled and mounted, remove the conical adapter an replace it with the supplied prime focus/eyepiece adapters. I used a feathertouch focuser on the conical adapter, and luckily I can continue to use it on the new prime focus adapter.

Again, after reinstalling the telescope on the AP1200, collimation remained nearly spot on and only a small tweak of the secondary mirror collimation was needed.

Here is an image of M15 made before and after the CDK conversion:

 Collimation can be tedious and  very small adjustments of the collimation screws are needed.  Unlike a Celestron or Meade SCT where there are  3 collimation screws on the secondary, the Mewlon has 3 pairs: for each pair one push screw and one pull screw. If you loosen the pull screw, the push screw needs to be tightened, if you want to tighten the pull screw, you need to loosen the push screw first.  To avoid dropping the Allen wrench in the tube, consider securing it in some fashion.  You need to do the collimation on a suitable star when the system is at or close to ambient temperature and with good seeing. The image below shows two recent conditions of collimation, one almost good (diffraction rings not quite concentric) and one good.  The stars are the double double star system in Lyra (there are four images in the image below, the distance  between the two pairs is much larger than shown when they would be imaged together at the focal length used).  This was taken with a DMK21AF618 at f/30.  There are still some seeing artefacts in the 14 July images, 500 images out of 1500 were stacked with Autostakkert!2.  Adjusting the screws will move the image in the eyepiece, you need to bring the star image back into the center of the field of view using the mount controls after each adjustment.  I prefer adjusting the colllimation at high magnification visually (I use a 3.8 mm eyepiece and to avoid atmospheric dispersion effects also a red filter)., but with good to excellent seeing you could use the image of a star given by a webcam, so you can adjust the collimation while viewing the monitor.