Re: [ATM] Couder Masks and Zone Testing

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Guy, Michael and Byron,

> 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,

This is not necessarily a good idea - particularly regarding the central
zone. At
http://w1.411.telia.com/~u41105032/couder/zcalc.htm
I have explained why I think so - in brief, a central zone does not behave
like the others, it is much less useful and better left out.

> It will help a LOT if you have a ruler that is marked
> in decimal fractions of an inch!

You could also use one marked in decimal fractions of a meter ;-)

> 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...

A possibly even slightly better solution is to make them of equal area, but
still use a chord (and diameter) to limit the cutouts. The reason is that
comparison is always along lines perpendicular to the (most commonly
vertical) knife-edge, and the extra "triangle" between the diameter and the
corresponding chord can only confuse. One way is to make the "height" of
each cutout about 1/3, or even 1/2 of the zonal radius.

Nils Olof



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