DIY 7 inch Cassegrain telescope - 2, OTA finished.

[Chanlunlun]

Dear ATMs,

After working for almost two weeks the OTA of the 7 inch Cassegrain is finished. My philosophy is to employ trash materials as far as possible and so the final outlook of the telescope is ugly. In these days “environmental friendly” is a slogan and so I have been trying to employ recycled materials as far as possible .

To make things simple I am working with plywood. They are free of charge, easy to handle and requires no special tools. For parts which require precision machining I use PVC rods. They are surplus materials from previous telescope projects. All materials are picked up from trash bins within our school.

One exception are the strusses – they are made by aluminium and aluminium cannot be found free of charge. But the cost of them is really small. I try to make things as cheap as possible. Spending big is always not my cup of tea.

With he OTA finished I can star test the whole optical system and make necessary figuring on the secondary mirror.

Best regards
Chan Yuk Lun
25 March 2012.

[Chanlunlun]

And more pictures.......

[funoooo]

Great scope.

[noodle]

[Eddy So]

[鄧登凳]

X2

[bingsze]

正啊！一點都不差！

[BossKwan]

Dear ATMs,

After working for almost two weeks the OTA of the 7 inch Cassegrain is finished. My philosophy is to employ trash materials as far as possible and so the final outlook of the telescope is ugly. In these days “environmental friendly” is a slogan and so I have been trying to employ recycled materials as far as possible .

To make things simple I am working with plywood. They are free of charge, easy to handle and requires no special tools. For parts which require precision machining I use PVC rods. They are surplus materials from previous telescope projects. All materials are picked up from trash bins within our school......

Ugly? What a piece of classic with wooden frame structure!

You always tease yourself about your craftsmanship, but the ugliness of your gears never prevents you from enjoying every your project..... also, good philosophy and good example of using trash materials....


By the way, what is the F-ratio of this cassegrain?
Also, I cannot see your trick from your photo, what meterials are you using for sticking(or holding) the mirror onto the wooden mirror cell?

[Chanlunlun]

By the way, what is the F-ratio of this cassegrain?

Original planed :- f/18.
After assembling everythjing and tested on site :- f/18.9

The discrepancy is due to the fact that the focal length of the primary is actually 29.18 inches instead of 28.00 inches.

If everything goes smoothly this long f/ratio makes a good planetary telescope.

Also, I cannot see your trick from your photo, what meterials are you using for sticking(or holding) the mirror onto the wooden mirror cell?

The primary is glued by double stick foam tape onto the plywood base. The tape is readily available in from every book store.

[anyone]

嚮往動手製作的魅力，奈何力不從心。
請問鏡神，這鏡子是目視用途嗎？

[Steve]

Chan Sir, no post about preparing the primary...may be it is too easy for you, haha

[Chanlunlun]

嚮往動手製作的魅力，奈何力不從心。
請問鏡神，這鏡子是目視用途嗎？

Yes, for visual only.

The aperture is too small for taking pictures.

[Chanlunlun]

Chan Sir, no post about preparing the primary...may be it is too easy for you, haha

Thanks for your comment.

However the primary mirror was made in 1976, 36 years ago while I was still a boy. By that time there was no internet nor personal computer.

Therefore there was no report on this mirror so far. Have you noticed that the edge of the mirror is red in color ? That was the color of red rouge, we used red rouge for polishing mirror by that time.

[Steve]

Chan Sir, no post about preparing the primary...may be it is too easy for you, haha

Thanks for your comment.

However the primary mirror was made in 1976, 36 years ago while I was still a boy. By that time there was no internet nor personal computer.

Therefore there was no report on this mirror so far. Have you noticed that the edge of the mirror is red in color ? That was the color of red rouge, we used red rouge for polishing mirror by that time.

Oh, ic, I thought it was recently made. 36年功力...

Is it Pyrex glass?

[Chanlunlun]

Chan Sir, no post about preparing the primary...may be it is too easy for you, haha

Thanks for your comment.

However the primary mirror was made in 1976, 36 years ago while I was still a boy. By that time there was no internet nor personal computer.

Therefore there was no report on this mirror so far. Have you noticed that the edge of the mirror is red in color ? That was the color of red rouge, we used red rouge for polishing mirror by that time.

Oh, ic, I thought it was recently made. 36年功力...

Is it Pyrex glass?

No, unfortunately I wasn't able to afford to buy Pyrex glass 36 years ago. I was born poor.

The glass is a very low quality porthole glass, with numerous gas bubbles inside. Fortunately it was well annealed.