Re: ATM 3-Vane or 4-Vane Spiders

["Bob May" <bobmay@nethere.com>]

Lets put it this way.  Each vane produces a percentage of the light being
diffracted.  3 vanes is 3x that amount of light.  4 vanes is 4x that amount
of light.  Now comes the fun.  The 4 vane spider produced spikes that
overlay each other.  Since the spikes are not coherent, they merely add to
each other.  In addition, the vanes usually aren't close enough to being
exactly opposite to each other so the light is just merely close enough so
that they only look like one spike rather than the true two spikes.  Then,
on top of that, the spikes are usually at slightly different angles due to
the vanes not being exactly parallel.  Thus, you get 8 spikes with a 4 vane
spider and 6 spikes with a 3 vane spider.  The 4 vane spider has brighter
spikes because the spikes pair up to double the brightness of each of the
visible spikes.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net