From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


>From: hermit 
>
>Russell Jocoy wrote:
>>
>>     ("atm{at}shore.net")
>>
>>          Hello all, I am in the process of making a Foucault / Ronchi
>> tester.  I have a Question about
>> the knife edge on the Foucault test. Does the knife edge have to come in
>> from the side ? or can
>> the blade "sweep" in like a clock hand.  I am asking
because , if I can
>> sweep the blade into the light
>> I can have a single pivot point.
>>       I am using a penlite for my light source with a diffuser in front,
but
>> this seems too bright. It may
>> be the penlite has a small lens in front of the bulb.
>>      I also mounted a viewing mirror next to the light source so I don't
>> have to view from behind and
>> can view from the side. Would there be any problems with this? I know
that
>> all my zones would be
>> on opposite sides from what is viewed but I is so much easier to view
from
>> the side.
>
>
>Make it as long a pivot as possible.  The problem will be in having it
>close to vertical when you get the shawdows.
>
>Ken
>
>

Hi
 You should have mentioned that the reason for having it
vertical is to minimize the distortion effects of having the mirror
supported from its edge while in a mount. At angles other than vertical,
the mirror doesn't see optically symetrical. Still, a couple of degrees
doesn't seem to have a lot of effect.
 If you are using a separate source, you'll loose some contrast
if the source edge isn't at the same angle as the resolving edge. If it
uses the moving source, like on a slitless, this isn't a problem.
Dwight

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