Re: ATM 14.5........focal legnth..72 .312

[Marty.T@t-online.de (Martin Trittelvitz)]

natsp schrieb:
 
> i made new ronchi screens too.
> i used a green led and put it on the knife edge holder.
> works good...
> ive either got a hole or a raised spot in  the mirror.
> im gonna look for a web page i saw that showed a bunch of screwed up
> mirror ronchi pictures.
> my lines bend in  twoards the center of the mirror kinda hour glass-looking.
> well  at least im learning somthing.

Hy! 
The ronchi screen is closer to the RoC (Radius of curveature) of the
zone when the lines are broader. So it depends if you are in front of
focus or behind, if its a raised spot or a hole. 
You can look in foucault, you have to see it there too. When the shadow
comes from the same side as the knife, then it is a mountain, when the
shadow comes from the opposit side then its a hole.
It is sometimes not so easy to decide if its a hole or a mountain.
If you want to finish your mirror you will have to learn this aniway.
marty

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