[ATM] Hill or hole?

["David Bevel" <dhcb@bellsouth.net>]

Hi All,



I have been wondering about an issue I have concerning Foucault images for a

while now and thought I would see what you folks have to say about my 
conundrum.



I have a mirror that has a problem. I have either a hill or a hole but not 
sure which.

Looking at images I have seen on various sights that provide examples of a 
hole and a hill

and having reviewed the remarks that accompanied the images I wonder how one 
can tell

what you have unless you know for a fact what either condition looks like in 
reference to

which direction your knife edge comes from  as it approaches the mirror. I 
would think your

image of the mirror produced with a knife edge that moves left to right 
would be a mirror of

one  produced with a rig that brought the knife edge in from right to left. 
In essence a mirror

defect could appear as a hole to one test rig and a hill to the other.

So lets say I have image taken with a left to right moving mirror and my 
image shows a deep

shadow on the left side of the hole/hill and a brighter area on the right 
while the rest of the

mirror outside the hill/hole is bright on the left and darker on the right. 
What have I got?

I also, hope I don't have any prints of the image upside down.;) Now for you 
highly intelligent

deep thinkers this may be blatantly obvious but to a fellow who gets 
headaches doing a simple

tax return uh, No!



Thanks in advance,



Dave Bevel 

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