From: "Pat Bunn" 
To: "Dale Eason" 
Cc: 
Reply-To: "Pat Bunn" 


As I said, I am doing this because I enjoy it. What I end up will be better
mechanically and will make fine adjustments easier- if it isn't necessary,
then who cares? I am using a dial indicator already. I am having fun, that
is why I am doing it. I asked a question and got an opinion which is what I
wanted. Thanks.

Pat Bunn


----- Original Message -----
From: "Dale Eason" 
To: "Pat Bunn" 
Cc: 
Sent: Saturday, August 02, 2003 12:59 PM Subject: Re: ATM Tester question


> Better in what way?  All that is required is that the
> light be a slit or a pin hole and if a slit that the
> return beam be stopped by a knife edge that is
> parallel to the slit.  A single knife edge placed over
> the led performs this function as good as anything
> else.  Led's are used in modern testers because you
> can get one that is as bright as you need, is
> monocromatic (green the color our eye is most
> sensitive to and what we usually figure the mirror to)
> and only requires low voltage and current to power.
> Other colors are available as well.
>
> The slitless tester as expressed by the Stellafane
> tester is actually the latest development.  It is a
> simplification of the original design that used a
> second blade to make a slit however it has been shown
> that the second blade is not needed and so the design
> has been simplified.
>
> The only part that needs to be very accurate is the
> foward and backward movement (in relation to the
> mirror) of the knife.  You need to be able to measure
> this to .001 inch.  As you can see in some of the
> pictures you can use a dial indicator that makes doing
> that easy.
>
> Because of the nature of the eye and the test it is
> hard without practice to get second readings for some
> zones that match withing .010 of the last time you
> read it.  After some practice some can do it within
> .005.  So using an indicator any better than .001 is
> not worthwhile and the data reduction does not need
> that kind of accuracy as well.
>
> If you use the indicator.  The threaded parts of the
> test are only used to move it not to measure it.
> However even those can be used to measure its movement
> to the accuracy required.  I used a micrometer to move
> my platform and a rubber band to keep the platform
> pressed against the micrometer.
> I have since replaced that with the dial indicator
> because it is easier to read than the micrometer but
> it is not more accurate.
>
> It is fine if you want to spend time making a prettier
> one but for me I would rather spend my time and
> resources on the scope itself or other things that
> truely need improving upon.  In my opinion there is
> nothing you can do to the tester that while help you
> make a better mirror.  Other are free to give thier
> opinion. So to get them I hope you don't mind that I
> post this to the ATM list as well.
>
> --- Pat Bunn  wrote:
> > I agree that the tester basis cannot be improved on,
> > but the mechanics of
> > the Stellaphane tester surely can be improved on
> > especially in the design of
> > the metrics . Maybe it is not necessary, but I 'd
> > rather do my measuring
> > with a decent threaded setup - something better than
> > two "T Nuts" and a
> > carriage bolt. I need the machining practice anyway
> > - that is the main
> > reason I am doing it a little different. What I am
> > looking for is has anyone
> > devised a better method of knife edge and LED ?
> >
> > Pat Bunn
> > ----- Original Message -----
> > From: "Dale Eason" 
> > To: "Pat Bunn" ; "John
Murray"
> > ;
> > "Amateur Telescope Makers" ; "Mirror
> > Matic"
> > 
> > Sent: Saturday, August 02, 2003 12:16 AM
> > Subject: Re: ATM Tester question
> >
> >
> > >
> > > Believe it or not the tester already has all the
> > > accuracy required and cannot easily be improved
> > upon.
> > > I am always amazed that such a simple device can
> > be
> > > used to make  extremely accurate measurments.
> > >
> > > You may already be aware of the updates to the
> > tester
> > > but if not here is a link.
> > >
> > >
> >
> http://www.stellafane.com/atm/atm_foucault_tester/atm_tester_plans_4.htm
> > >
> > > --- Pat Bunn  wrote:
> > > >
> > > > I am just beginning to assemble a "Stellaphane"
> > type
> > > > tester with some
> > > > machined aluminum and brass parts ( I have spent
> > the
> > > > last week machining
> > > > these - I am not a machinist), rather than the
> > wood
> > > > mechanics.
> > > >
> > > > I am using 3/4" birch plywood with a nice
> > > > polyurethane finish and a metal
> > > > vernier mechanism and slide arrangement. My
> > stage
> > > > "faceplate"  is 1/4"
> > > > delrin sheet rather than 1/4 " plywood.
> > > >
> > > > Any ideas or improvements on the light source
> > and
> > > > slit arrangement or is the
> > > > published design good enough. I am trying for a
> > more
> > > > accurate design than
> > > > the basic wood design.
> > > >
> > > > Pat Bunn
> > > >
> > > >
> > >
> > >
> > > __________________________________
> > > Do you Yahoo!?
> > > Yahoo! SiteBuilder - Free, easy-to-use web site
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> > >
> > >
> >
>
>
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