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Is B58-53 problem glass?

Started by klawson, 11/19/2004 07:46PM
Posted 11/19/2004 07:46PM | Edited 11/19/2004 07:58PM Opening Post
Here is a screen capture shot of the performance of a corrector I worked on using Corning B58-53 glass (yes, I know others have been down this road). The attached file shows the on axis performance. Screen 1 in the picture shows the final color spots to be well within the airy disk. I have other examples if anyone is interested. Coor2.jpg will show the on axis performance with the corrector knocked out of alignment. The corrector is tilted 1/2 degree and is moved off the axis by almost a 1/4 of an inch. All the color spots are still within the airy disk. Coor3.jpg will show the on axis performance at the edge of a 1/2 degree field of view. It's still almost diffraction limited at this extent. The curves on the corrector are gentle and it's a oiled triplet. The primary objective (203mm F/15) is designed as an oiled doublet using common glass. The corrector is only 85mm in diameter. I've run the design through another optics program and I get the same result. Can anyone tell me what the problem is with this approach? Is Corning B58-53 a problem? Price, availiability, etc. I can post the other files if anyone is interested.

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klawson's attachment for post 20282

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Posted 11/20/2004 10:40AM #1
>Can anyone tell me what the problem is with this approach? Is Corning B58-53 a problem? Price, availiability, etc. I can post the other files if anyone is interested.>

I have made a number correctors for large achromats, the last one for a 10" F15 Zeiss. The glass does work in this application. It is a relatively soft glass, similar to fluorite, and will break easily if heated or cooled quickly. You may have extreme trouble getting any in good quality levels or even at all, since Corning France is essentially out of business and melts only the most common crowns now. I have a few pieces left and they all show striations and non-homogeneity. There are other ways to accomplish this function without using this troubling glass.

Roland Christen