Mel Bartels的創意折曡牛反

[bbsdma]

13.2" F/3.0

更多圖片訢賞：
http://www.bbastrodesigns.com/ZipDob/ZipDob.html

3D糢型
http://sketchup.google.com/3dwarehouse/ ... c&hl=zh-CN

[Eddy So]

好設計！

[Wah!!]

[Chanlunlun]

Dear ATMers,

Vey nice telescope design.

Notice that for the design to be successful you absolutely need a very fast mirror - an f/3 to say the least. And the mirror should be in meniscus form otherwise the center is too thin.

A f/3 meniscus paraboloid is very difficult to obtain if it is not home brewed by yourselves. Even money cannot always solve this problem.

Best regards
Chan Yuk Lun

[bbsdma]

Dear Chan Sir,
Why it is necessary to use meniscus shape instead of simply increase the thickness to cope with the thickness loss of the center zone? Any way, the sagitta for a 13" F/3 mirror is "mere" 7 mm.

[Chanlunlun]

Dear Chan Sir,
Why it is necessary to use meniscus shape instead of simply increase the thickness to cope with the thickness loss of the center zone? Any way, the sagitta for a 13" F/3 mirror is "mere" 7 mm.

Dear Mr/Miss bbsdma,

If the center of the mirror is too thin it will break easily. We once had a 30 inch f/2.8 mirror with centeral thickness of only 9 mm, ( the sagita is about 16 mm ) and it broke during a trip.

A second identical mirror was made. Despite of its giant size and massive light grasp we dare not take it out since we are afraid of breaking it again.

Another side effect of too thin central thicknes is that the mirror will wrap quite easily. A very complicated mirror cell must be made. A meniscus mirror is being much stronger and thus simplifies the construction of the miror cell.

Best regards
Chan Yuk Lun

[bbsdma]

Dear Chan Sir,
Why it is necessary to use meniscus shape instead of simply increase the thickness to cope with the thickness loss of the center zone? Any way, the sagitta for a 13" F/3 mirror is "mere" 7 mm.

Dear Mr/Miss bbsdma,

If the center of the mirror is too thin it will break easily. We once had a 30 inch f/2.8 mirror with centeral thickness of only 9 mm, ( the sagita is about 16 mm ) and it broke during a trip.

A second identical mirror was made. Despite of its giant size and massive light grasp we dare not take it out since we are afraid of breaking it again.

Another side effect of too thin central thicknes is that the mirror will wrap quite easily. A very complicated mirror cell must be made. A meniscus mirror is being much stronger and thus simplifies the construction of the miror cell.

Best regards
Chan Yuk Lun

Dear Chan Sir,

I understand the risk of the combination of ultra-thin mirrors and a deep curve.

But my point is, beside utilizing meniscus blank to preserve the central zone thickness for a ultra-ultra thin mirror, isn't that a better idea to work with moderate thickness flat blanks ?

[Chanlunlun]

Dear Chan Sir,
Why it is necessary to use meniscus shape instead of simply increase the thickness to cope with the thickness loss of the center zone? Any way, the sagitta for a 13" F/3 mirror is "mere" 7 mm.

Dear Mr/Miss bbsdma,

If the center of the mirror is too thin it will break easily. We once had a 30 inch f/2.8 mirror with centeral thickness of only 9 mm, ( the sagita is about 16 mm ) and it broke during a trip.

A second identical mirror was made. Despite of its giant size and massive light grasp we dare not take it out since we are afraid of breaking it again.

Another side effect of too thin central thicknes is that the mirror will wrap quite easily. A very complicated mirror cell must be made. A meniscus mirror is being much stronger and thus simplifies the construction of the miror cell.

Best regards
Chan Yuk Lun

Dear Chan Sir,

I understand the risk of the combination of ultra-thin mirrors and a deep curve.

But my point is, beside utilizing meniscus blank to preserve the central zone thickness for a ultra-ultra thin mirror, isn't that a better idea to work with moderate thickness flat blanks ?

Dear bbdsma,

Your suggestion is very reasonable.

But Mel Bartel is no ordinary ATMer - he likes to face difficult technical challenges. Do you know he has himself accessment to a klin to melt and temper the glass ?

That's why he could afford to experiment a menuscus shape mirror blank. Nevertheless for an 13 inch f/3 mirror I do agree that any ordinary 1 inch thick float glass would certainly serve the purpose very well.

Best regards
Chan Yuk Lun