The making of 26 inch Cassegrain -18, Secondary ring done.

[Chanlunlun]

Dear ATMers,

The secondary assembly consists of the secondary mirror, mirror cell, supporting spider and a shield tube.

The supporting spider was first finished. It has to be tested by attaching the secondary mirror onto and see how rigid it is. The secondary mirror is a 9.5 inch diameter hyperbolic mirror which weights quite heavily. In order to minimize the weight we carefully choose a glass blank of thickness 3/4 inch. Nevertheless the weight of the secondary still exceeds 2 kg, much heavier than an ordinary diagonal mirror.

We gladly discovered that the spider is totally rigid enough to support the hanging secondary mirror. ( in using the secondary mirror is facing downwards ).

We finally constructed the light shield tube by cardboard paper which serves the purpose very well – light weight and rigid.

The whole secondary assembly was then finished. At the same time we also completed the diagonal mirror cage, with focuser and finderscope base fixed.

The whole OTA is completed. The next is to test its center of gravity. That is another big job.

Best regards
Chan Yuk Lun
19 March 2015

[Eddy So]

[wtyu21]

GREAT JOB～

[Chanlunlun]

GREAT JOB～

It's real big.

To handle with the sizable component may be the most challenging part of the job.