Re: [ATM] fringe testing three flats

["Jeff Baldwin" <bald@centurytel.net>]

I use small triangular pieces of cellophane, like a CD wrapper cut up, 
placed between the glasses at the edges with the points towards the center. 
As you pull on one slowly you will alter the gap at that corner and you can 
do that without pushing down on the glass, which changes the shape and can 
cause misjudgment of the figure.  Also, the further back you go the more 
accurate the fringe image will be.  Go all the way to the other side of the 
room and use a telephoto lens to image the fringes.  5 to 7 dark lines ought 
to be a more manageable job than 10 - 15.  It will also be easier to measure 
the amount of bend and therefore the factions of waves the two glasses 
differ by.  Enjoy.
JBald

Jeff and Glenda Baldwin
Beaver WA
http://home.centurytel.net/bald



> I've taken to pressing on one edge to de-center the bull's eye enough to
> get more or less straight fringes across the disk, I usually aim for
> about 10-15 fringes.
>
>
> Clear Skies, Thomas. 

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