DIY 7 inch Cassegrain telescope - 3, star test

[Chanlunlun]

Dear ATMs,

The purpose of making the tube assembly prior to the optics itself is to carry out star test. As mentioned before the primary mirror is already parabolic, the aim of the star test is to test the figure of the secondary.

Star test doesn’t need a real star. My target is a distant crystal chandelier. The reflection on the hanging “crystal” surfaces form perfect point sources.

The test result was short of surprising – the “star” image showed overcorrection, as predicted by prior computer simulation. A spherical secondary is bound to produced overcorrected images in a classical Cassegrain.

Naturally my next job is to change the spherical surface of the secondary into a hyperboloid. Don’t worry, I’ll post my method here – the secret of making the hyperboloid secondary mirror.

Best regards
Chan Yuk Lun
16 April 2012.

[marco1415]

Well done!!幾時帶去PTC??

[Eddy So]

[anyone]

好靚仔！

[Chanlunlun]

Well done!!幾時帶去PTC??

No today, not tomorrow, but soon.

[wtyu21]

Dear MG，Why dont you using a plastic water tube for the main body for your new baby？ I saw there are 10“ in diameter water tubes sell on the market once～

[Chanlunlun]

Dear MG，Why dont you using a plastic water tube for the main body for your new baby？ I saw there are 10“ in diameter water tubes sell on the market once～

Thanks a lot for your suggestion. However there are three resons prohibit me from choosing a big PVC tube :-

1. Expensive.
2. Heavy.
3. Circular parts are difficult to work with.

[funoooo]

期待中！

[lawrencemok]

Chan Sir, will you show off this in QC open day?

[Chanlunlun]

Chan Sir, will you show off this in QC open day?

This small prototype Cassegrain will not be displayed in upcoming Open day ( 20,21 April ) but If you come I will of course show you personally.

A lot of other equipment will be shown, including a 14 inch Planetary Newtonian. I belief this telescope will be more attractive than the small Cassegrain.