Re: [ATM] Couder Masks and Zone Testing

["Byron" <byron@astronomygeek.us>]

Thanks Guy, I am going to have chew on it a bit.... with blue smoke rolling
out of my ears... but I will get it. ;-)

If you could send me a bitmap like you suggested, I would appreciate it..

Byron

----- Original Message -----
From: "Guy Brandenburg" <gfbrandenburg@yahoo.com>
To: "Michael Lindner" <mikell@optonline.net>; "Byron"
<byron@astronomygeek.us>; <atm@atmlist.net>
Sent: Wednesday, April 14, 2004 3:47 PM
Subject: Re: [ATM] Couder Masks and Zone Testing


> Michael and Byron,
>
> Rather than messing around with trying to make a
> post-script printer behave properly, I find it to be
> much simpler to use a calculator, a good ruler, a
> compass, and a sharp single-edge razor blade to make a
> decent Couder mask. Also, one innovation I gleaned
> from Michael Mills (of NOVAC) is to have all of the
> 'holes' in the mask be the same area by using
> diameters to draw them, rather than parallel chords.
> Plus, this all makes it much easier to construct the
> mask on relatively durable cardboard of some sort.
>
> The math is not hard, really. If you have a 6 inch
> diameter mirror, and you want 4 zones, and you want
> them to have the same area, then simply think about
> what the area of the mirror is, and divide it by 4.
> The area formula for a circle is pi * r^2, or 9*pi.
> (It's actually much less work if you leave everything
> in terms of pi.)
>
> So each zone will have an area of 9/4 * pi, or 2.25 *
> pi. That means that the radius of the first zone must
> be the square root of 9/4 or the square root of 2.25,
> or 1.5 inches (1 1/2 ").
>
> Result: you draw a circle with a radius of 1.5 inches.
>
> The next zone needs to have the same area, but is
> built around the first zone; so we can add 2.25*pi to
> itself, to get 4.5*pi for the area of both regions.
> And, since the area of a circle is pi * r^2, that
> means that the outer radius of the second zone is the
> square root of 4.5 - or, if you like, the square root
> of 2 times 1.5, which is about 2.12 inches.
>
> It will help a LOT if you have a ruler that is marked
> in decimal fractions of an inch!
>
> The third zone, to cut things short, will have a
> radius that is 1.5 inches times the square root of 3.
>
> And the fourth zone has a radius of 1.5 inches times
> the square root of 4. But, hey - that's just 2. Thus,
> the last zone will have a radius of 1.5 inches times
> 2, or 3 inches. But, hey - that means we came to the
> end of the mirror.
>
> In general, if you want to divide a mirror of radius R
> (= D/2) into N zones of equal area, the first zone
> will have an outer radius that has length R divided by
> the square root of N, which quotient I will perversely
> call Z . Then, for subsequent zones, you merely
> multiply Z by the square root of 2, then the square
> root of 3, then the square root of 4 (aka 2), the
> square root of 5, the square root of 6, and so on,
> until you get to the square root of N, at which the
> square roots of N both cancel out and you have arrived
> at the edge of your mirror.
>
> As far as what portion of the zone to cut out, both
> Texereau and the LeCleires suggest drawing chords that
> are parallel to the diameter, and cutting between the
> chords. The problem here is that the outer zones
> become much, much smaller than the inner zones, and
> thus are harder to read. A simpler and better solution
> (IMO) that I stole from Mike Mills, as I mentioned, is
> to draw two more diameters, separated from the
> horizontal diameter by something like 45 degrees. Then
> cut out alternate swaths of the zones that are
> alternately above and below the horizontal diameter,
> but are contained between the two other diameters.
>
> There is no way I can draw this in ASCII art, but if
> you want I could send you a bitmap image that
> illustrates the general idea.
>
> Guy Brandenburg
>
>
>
> --- Michael Lindner <mikell@optonline.net> wrote:
> > On Wednesday 14 April 2004 01:37 pm, Byron wrote:
> > > I have read some of about creating a Couder mask,
> > but right now I would
> > > like some type of software or anything that will
> > make creating the masks
> > > easier. I can always grasp a greater understanding
> > of it as I go along.
> >
> > Tex will also generate a printable couder mask.
> >
> > http://home.att.net/~mikel/
> >
> > --
> > Michael Lindner
> > http://www.starastronomy.org ***
> > http://home.att.net/~mikel
> > http://www.atmsite.org *** http://www.atmlist.net
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
>
>
> =====
> Guy  BrandenburgWashington,
DChttp://home.earthlink.net/~gfbranden/GFB_Home_Page.html
>
>
>
>
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