The making of 26 inch Dall Kirkham telescope - 1, design.

[Chanlunlun]

Dear ATMers,

After lying dormant for several years, our mirror making group is awaking now. Of course small student are always dreaming of making big telescope. Below is the specification of our new telescope which is coming into construction soon :-

Aperture – 26 inches.
Focal length – 260 inches at f/10.
Type – Dall Kirkham Nysmith ( DKN )
Primary mirror thickness – as usual, 1 inch, float glass.
Primary mirror cell – 27 points floatation.
Primary mirror profile – Ellipsoid, conic constant = 0.76
Secondary mirror – spherical , diameter = 9.5 inches.
Tertiary mirror – elliptical diagonal flat mirror, 2.6 inches minor axis.
Zenith eyepiece height – approximately 60 inches.
Mechanical style – Alt-azimuth with GOTO and tracking capability.
Weight – expected no less than 100 kg

Although we made a 30 inch telescope, it has never been put into use because of its too aggressive design which is not practical. Though 4 inches smaller in aperture, this 26 inchers will still remain as the biggest working telescope in Hong Kong after its completion.

Best regards
Chan Yuk Lun
3 September 2013.

[Steve]

Wow...very aggressive design, too

每次裝拆後Alignment 容易嗎?

祝願成功

[anyone]

祝早日完成大鏡！

[Chanlunlun]

Wow...very aggressive design, too

每次裝拆後Alignment 容易嗎?

祝願成功

Comparing to the previous 30 incher design this project is very conservative.

1. The 30 inch mirror has a very fast f/2.8 while in this project we employ a primary mirror of f/7.5. This very shallow mirror requies only little rough grinding and, most of all, retaining a very thick central mirror thickness which again ensure mechanicl stability of the glass disk.

2. The 30 inch telescope is designed to be taken out for star gazing , i.e. a portable design. A portable 30 inch telescope is too agrresive. This 26 incher is designed "in-house". That is, this telescope will never leave the roof of our school, thus enable us to be free from "weight" factor.

3. The 30 incher desined to be as light weigh as possible thus sacrificing mechanical stability. The primary mirror is so thin ( due to light weight design ) that it breaks by itself during transportation. For the present 26 inch project a thicker mirror is welcomed ( although we are currently designed with a 1 inch glass disk but thicker glass disk could also be used) since the weight factor is out of question.

4. The GOTO may sound very complicated but it's nothing that horrible. You've seen it in PTC.

[Steve]

Wow...very aggressive design, too

每次裝拆後Alignment 容易嗎?

祝願成功

Comparing to the previous 30 incher design this project is very conservative.

1. The 30 inch mirror has a very fast f/2.8 while in this project we employ a primary mirror of f/7.5. This very shallow mirror requies only little rough grinding and, most of all, retaining a very thick central mirror thickness which again ensure mechanicl stability of the glass disk.

2. The 30 inch telescope is designed to be taken out for star gazing , i.e. a portable design. A portable 30 inch telescope is too agrresive. This 26 incher is designed "in-house". That is, this telescope will never leave the roof of our school, thus enable us to be free from "weight" factor.

3. The 30 incher desined to be as light weigh as possible thus sacrificing mechanical stability. The primary mirror is so thin ( due to light weight design ) that it breaks by itself during transportation. For the present 26 inch project a thicker mirror is welcomed ( although we are currently designed with a 1 inch glass disk but thicker glass disk could also be used) since the weight factor is out of question.

4. The GOTO may sound very complicated but it's nothing that horrible. You've seen it in PTC.

I SEE, 原來是固定使用的重型武器

[Chanlunlun]

Wow...very aggressive design, too

每次裝拆後Alignment 容易嗎?

祝願成功

Comparing to the previous 30 incher design this project is very conservative.

1. The 30 inch mirror has a very fast f/2.8 while in this project we employ a primary mirror of f/7.5. This very shallow mirror requies only little rough grinding and, most of all, retaining a very thick central mirror thickness which again ensure mechanicl stability of the glass disk.

2. The 30 inch telescope is designed to be taken out for star gazing , i.e. a portable design. A portable 30 inch telescope is too agrresive. This 26 incher is designed "in-house". That is, this telescope will never leave the roof of our school, thus enable us to be free from "weight" factor.

3. The 30 incher desined to be as light weigh as possible thus sacrificing mechanical stability. The primary mirror is so thin ( due to light weight design ) that it breaks by itself during transportation. For the present 26 inch project a thicker mirror is welcomed ( although we are currently designed with a 1 inch glass disk but thicker glass disk could also be used) since the weight factor is out of question.

4. The GOTO may sound very complicated but it's nothing that horrible. You've seen it in PTC.

I SEE, 原來是固定使用的重型武器

Yes. When no transportation factor is involved, we gain higher degrees of freedom for designing. In particular we can make a heavier telescope to gain more stability.

And we may add GOTO to serve the scope either.

[lawrencemok]

great project! to be finished in this year?

[Chanlunlun]

great project! to be finished in this year?

Planned to be finished before open day next year.

[bingsze]

how about secondary mirror ? Is it easy to grind as well? Or this is the bottleneck of your project?

[benzenechow]

萬二分期待26吋到北潭涌觀星既一天呀,,,,,,!!^^

[Chanlunlun]

how about secondary mirror ? Is it easy to grind as well? Or this is the bottleneck of your project?

The secondary mirror is very easy, it is spherical. Actually the secondary mirror was finished before summer vacation.

[Chanlunlun]

萬二分期待26吋到北潭涌觀星既一天呀,,,,,,!!^^

Regret to say that it's not quite possible. The telescope will be too heavy to be portable.

[benzenechow]

咁陳SIR,,,,你會唔會係你果度攪番個STAR PARTY!!^^?其實確實位置會放在哪裏呢,,,,市區光害太嚴重,,,,!!26吋會浪費他呢,,,,!!@@

[Chanlunlun]

咁陳SIR,,,,你會唔會係你果度攪番個STAR PARTY!!^^?其實確實位置會放在哪裏呢,,,,市區光害太嚴重,,,,!!26吋會浪費他呢,,,,!!@@

Of course we definitely will. Our roof is very large.

[bingsze]

報名！