[ATM] how to fix a zone and understanding small tool action

[Dale Eason]

You have confused me a little.  If you use a Ross null
then you are testing relative to a sphere I think.

Unless that is a typo.  Then I wonder if you are using
the null correctly.  Perhaps it is confusing the
issue.  There would be less confusion with a Foucault
test even first timers get the actual figure close and
would be able to tell easily which way the zone goes. 
It is always good to have a second test method and
then if they match you are more assured of your
results.

I am not against the ronchi test except first timers
sometime have trouble interpreting the results.  


Dale Eason

--- Mark Yama <myama at uidaho.edu> wrote:

> Dear list members,
> I hope you can help me with some major confusion.  I
> have been working with a 25 in mirror and trying to
> get a good figure for a long time.  Eventually I
> obtained a raised zone about 2 inches wide, centered
> 3 inches from the edge.  It seemed reasonable to try
> to fix this with a small tool.  I had one, around 2
> inches in diameter and then proceeded with short
> tangential strokes right over this region.  Here are
> some additional details: I am mostly testing with
> the Ronchi test, with a Ross null lens.  Thus the
> deviations I see are relative to a parabola, not a
> sphere.  Anyway, the small tool seemed ineffective,
> so I continued for longer and longer periods. 
> Eventually I woke up to the realization that thing
> were getting worse.  In particular, I dug a ditch on
> the outside of the raised zone.  I would like help
> a) in understanding why this happened and b) some
> suggestions for curing both the raised zone or the
> neigboring ditch.  Besides beginning to doubt my
> sanity I have been wondering if my interpretation of
> a raised area is somehow wrong, and that maybe it
> would be better to think of a zone where the slope
> of the curve on the glass is angled slightly so that
> that zone in question focuses long.  Any help and
> education would be much appreciated, believe me.
>  
> Mark Yama
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 



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