The making of 30 in telescope - 30, mirror cell finished

[Chanlunlun]

Dear ATMs,

The mirror cell for the 30 inch has just been completed. It was once planned to be a 27 points floatation but after careful calculation we decided to make it a 18 points. The completed cell has a huge outlook.

Upon completion we tested the cell to see whether it supports the mirror symmetrically. The mirror was arranged to ride onto the mirror cell and point to a distance object. A building wall would be a a nice target. A 12 mm eyepiece was used to view straight back into the mirror ( actually the mirror is used as it is in a real telescope ) giving a magnification of about 200 X. If the horizontal and vertical lines on the wall both appearing sharp at the same time, astigmatism is absent.

We have tested the mirror cell and found that it is good. It supports the mirror symmetrically. So far so good.

We are looking forward to complete the whole telescope in the short future.

Best regards
Chan Yuk Lun
13-1-2006

[Tarepanda]

好通透~~
打算怎樣鍍法?

[XR250]

主鏡座都已經製好，應該好快可以first light!

[Chanlunlun]

好通透~~
打算怎樣鍍法?

Dear Mr. Panda,

Originally the mirror is planed to be silvered. We have bought 1 kg of silver nitrate in order to to finish this job.

Not until recently we have discovered that there exists a firm in mainland who is able to help to aluminize the mirror. The firm has a very large vacuum chamber (exceed 1 m in diameter ) that can take care of the 30 inch mirror.

The problem now becomes : how to transport the mirror to and back from mainland China ?

Best regards
Chan Yuk Lun

[Tarepanda]

你所指的公司該不會是晶華吧?運輸確實是個大問題
內地的運輪真的很不可靠,有時真要看運氣
不知道你之前的20寸和24寸又是如何完成
鍍鋁這過程的?畢竟它們也不小

[Astrocat]

Not until recently we have discovered that there exists a firm in mainland who is able to help to aluminize the mirror. The firm has a very large vacuum chamber (exceed 1 m in diameter ) that can take care of the 30 inch mirror.

Chan Yuk Lun

Dear Chan sir,

Do you think there is a need of custom-made device to hold the mirror inside the chamber depending the size of the mirror?

[Chanlunlun]

Not until recently we have discovered that there exists a firm in mainland who is able to help to aluminize the mirror. The firm has a very large vacuum chamber (exceed 1 m in diameter ) that can take care of the 30 inch mirror.

Chan Yuk Lun

Dear Chan sir,

Do you think there is a need of custom-made device to hold the mirror inside the chamber depending the size of the mirror?

Dear Mr. Astrocat,

Yes we do.

We need to custom made a holder to hold the mirror, face downwards, vertically above the tungsten filament inside the chamber. Don't worry - the holder is very easy to fabricate. It will not take us more than half an hour to finish the job.

The real problem is how to transport the mirror to and back from mainland safely. In case I think I will travel along with the mirror.

Best regards
Chan Yuk Lun

[少爺]

好通透~~
打算怎樣鍍法?

Dear Mr. Panda,

Originally the mirror is planed to be silvered. We have bought 1 kg of silver nitrate in order to to finish this job.

Not until recently we have discovered that there exists a firm in mainland who is able to help to aluminize the mirror. The firm has a very large vacuum chamber (exceed 1 m in diameter ) that can take care of the 30 inch mirror.

The problem now becomes : how to transport the mirror to and back from mainland China ?

Best regards
Chan Yuk Lun

how to do it by silver nitrate?

[simonii]

好期待到時見到d乜

[CK]

Chan Sir

有一事請教，用圓頭螺絲，與玻璃只有一相當小接觸面，會否令主鏡壓力太集中？

我以往的做法是每口螺絲用雪佛龍車一個凹型墊，將螺絲頭藏入，用雪佛龍墊支撐主鏡，分散壓力，方法是否正確？

謝！！

ck

[Chanlunlun]

Chan Sir

有一事請教，用圓頭螺絲，與玻璃只有一相當小接觸面，會否令主鏡壓力太集中？

我以往的做法是每口螺絲用雪佛龍車一個凹型墊，將螺絲頭藏入，用雪佛龍墊支撐主鏡，分散壓力，方法是否正確？

謝！！

ck

Dear CK,

Thanks for your comment.

Actually I was asked the same question many times before. In my opinmion it is not wise to spread out the pressure by introduction of pads of telfon or other material due to the following reasons :-

1. It complicates the cell design.
2. The total weight of the mirror is about 40 lbs, so each "point' has an average contact force of about 2 lbs, not a very big value. The pressure thus introduced in each contact point is not that large as you imagine. ( Just the same as you are lying on nail bed, you don't feel the pain at all because the pressure on each sharp nail point is small )
3. The pad cannot have a perfect contact with the miorror back, thus we are losing control on how big the contact force on each supporting pads. The mirror cell may not work as planned.
4. The friction between the pad and glass mirror back surface, which is un-predictable and out of our control, will also affect the working status of the floatation cell.
5. In computer simulation the mirror is supported by sharp points, which is exactly the same what we are doing now.
6. We have made two of these floatation cell before ( 20 inch telescope, 24 inch telescope ) and they are working fine.

So again thanks for your concerns about the 30 inch project. The project is approaching to its end now and when the students are finished with their half-yearly examination we will resume to full working status again.

The first light of the biggest telescope in Hong Kong, I believe, will not be far away.

Best regards
Chan Yuk Lun

[CK]

Thank for your opinmion !!

ck

[Subaru]

好野, 就快有大鏡睇! 我都prefer鍍鋁(要有overcoating), 個reflectivity比銀無差得噤快, 起碼用十年.

[Chanlunlun]

你所指的公司該不會是晶華吧?運輸確實是個大問題
內地的運輪真的很不可靠,有時真要看運氣
不知道你之前的20寸和24寸又是如何完成
鍍鋁這過程的?畢竟它們也不小

Dear Mr. Panda,

The company is not Maxvixion.

The 20 inch is aluminized in Hong Kong. the 24 inch is silvered by ourselves.

In the worst case we may silver the 30 inch as well, only that the life time of the coating is limited to one year.

Best regards
Chan Yuk Lun