Re: [ATM] Improving my focault tester / testing skills

[Dale Eason <atmpob@yahoo.com>]

The eye responds to movement better than slight
differences in grey shades.  It helps to jiggle the
tester just a tiny bit by slight pressing on the table
it is sitting on.  That will make the zones wink out
quickly.  It can be easier to detect when both are
winking out at the same time that way.  You want to
make it jiggle into the beam and not closer to the
mirror.

One color usually does not help.  I find that each
type of tester is about the same for me.

What F number and diameter are you testing.  Very slow
mirrors can be very hard.

It could also be that you are very close to a sphere
then all zones dim at the same time.

Another technique is to move the test closer to the
mirror until you are sure the zone does not null. 
Then move it the other way until once again it does
not null.  Then divide the two readings to find the
middle where it does null.



Dale Eason
--- Emil Johnsen <emil@lei-en-nerd.no> wrote:

> Hi,
> 
> I'm looking for some advice on how to improve my
> foucault tester, or 
> possibly just my skills at using it.
> 
> It's a slitless tester and the light source is a
> small flaslight bulb.
> 
> My problem with the tester is that when I do zonal
> relading with a 
> couder mask I find it very hard to se which side
> becomes dark first. I 
> can tell when I'm some distance inside or outside
> ROC, but there is a 
> wide range where the two sides appear to gray out at
> the same time.
> 
> Is this problem an iherent limitation of the
> slitless tester?
> 
> Is there some special technique to tell shich side
> grays out first?
> 
> How important is the size and brightness of the
> light source?
> 
> Would a light source emitting mostly one color be
> better?
> 
> 
> --
> Emil Johnsen
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 



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