403mm已经开磨，设计图纸及镜子现状

[潘昭宇]

403mm设计图纸

[潘昭宇]

403mm磨镜现状，预计焦比f4的，80号金刚砂7天了，中间下去了2.5mm，粗磨预计4.35mm深，不吻合，有大气泡

[Wah!!]

12點浮動支撐比較少見, 一般由9跳上去就是18點呢.

努力! 加油!

[Eddy So]

努力！加油！ [衝刺運球]

[Chanlunlun]

Dear Mr. Poon,

There is a major flaw in your mirror cell design. Your floating points are in 4 groups instead of three.

How could you make sure that all the 12 points are in equal contact with the mirror back surface at the same time ?

Since your mirror blank is so thick, there is absoluetly no need to use floataton system. Double sided foam gluing tape is already good enough. My 16 inches mirror has a thickness of 1 inch onmly. It shows no astigmatism even using 6 points double glue.

Best regards
Chan Yuk Lun

[Wongsir]

Mini Poon,.

Hi! Good work.

It takes me sometime to find out the information about designing the cassegrain telescope.

For classical cassegrain, the secondary mirror should be a convex mirror.
The focal ratio of the parabolic primary mirror is around f/3~ f/4.
With different focal ratio of the hyperbolic secondary, the combined final focal ratio is about f/9 ~ f/13.
For RC cassegrain it is about f/8.
You should determine the size of the secondary so that you limit the percentage of obstruction, that is how much light is blocked by the secondary mirror, this will affect the sharpness of the image.

Reference:
1) Telescope Optics
http://www.telescope-optics.net/two-mirror.htm
2) DFM
http://www.dfmengineering.com/cct_16.html
3) RCOS
http://www.rcopticalsystems.com/telescopes/


Wongsir
2010-01-03

[Wongsir]

Formula for the Casegrain telescope....

Reference:
Harrie Rutten, Martin van Venrooil, Willmann bell, 1989, Telescope Optics Evaluation and Design pp61~62

Wongsir
2010-01-03

[Wah!!]

Dear Mr. Poon,

There is a major flaw in your mirror cell design. Your floating points are in 4 groups instead of three.

How could you make sure that all the 12 points are in equal contact with the mirror back surface at the same time ?...

I think it is possible to use 4 groups @ 2x2

But the main problem could be the PLOP software may not support such cell design...

[潘昭宇]

改为9点支撑，见图

[苏鲁锭]

一下子磨制400mm卡式。跨越太大了。
主镜口径400，焦比F4
要求遮挡比1/4.成像点在主镜后面300mm

系统焦距6000mm.
也就是F15

[苏鲁锭]

主镜口径400 .中心曲率半径 3200mm K= -1
副镜口径100，中心曲率半径 1090.8784mm K= -2.983206

[苏鲁锭]

视场0.24度。
星点都可以小于艾利斑。
可以说是完美的。
唯一的缺点是焦距太长视场小。

[Wah!!]

王師傅計算的是 RC 鏡吧?
若是 DK 應該較容易磨.

[潘昭宇]

谢谢王师傅的帮忙

[苏鲁锭]

王師傅計算的是 RC 鏡吧?
若是 DK 應該較容易磨.

主镜 k-1 是经典卡式。