Offset Spider Vane
that also incorporate the Diagonals
This photo shows the offset spider configuration and were
the Diagonal offset takes place.
This is what an offset spider looks like, at
first glance it will seem quite odd looking and that it might produce
8 diffraction spikes but this is not the case, it still forms the traditional
4 spikes even though the vanes do not meet at center. The main benefit
to an offset spider is its resistance to rotational movement over time,
in other words how many times have you tightened your diagonal center bolt
and found later that somehow it moved in rotational adjustment and you
are right back where you started from twisting back and forth on the
center bolt with a wrench. You see most commercial spiders use a diagonal
holder that requires you to tighten two nuts with an open end wrench, this
has to be the biggest mistake ever made by manufacturers its just creates
a frustrating exercise in alignment. As you can see from the pictures I
have not fallen into this trap, with mine you just pop in the holder rotate
it, tighten two set screws and push the safety clip on. To do the fine
adjustments I used 4 bolts not 3, I can't say anymore here, once you try
it you will realize the advantage. Another property of the spider is the
lack of tension required to support it in a tube, people who use sonotube
will experience no depression where the support bolts go through, because
it becomes ridged with only finger tight tension.
SPEC'S & SOME COMPARISONS
MIRROR PLACEMENT= is accomplished
by 3 equal siliconed points. Some advantages
to silicon over shell supports are, quicker equilibrium to outside
temp.( no trapped air as in shell ), full use of aluminized surface
( giving less obstruction ), no chance of falling off or going out of
alignment ( due to loose screws ), no pressure against mirror ( as a
head shell is not the way we support other optics, pushing on the back
and pulling on the front? ) easier to clean ( no disassembly ), you can
use different diagonal sizes on the same holder ( no need to purchase
another holder ).
CENTER SHAFT = (1/4" shaft for 1.5" , 2.1" diagonals)(5/16" shaft for 2.6" , 3.1"diagonals) and (3/8"
shaft for 3.5"diagonals) all
shafts are Stainless steel and have a safety clip.
ADJUSTMENT = 4 point using stainless steel button head bolts.( 3 adjustment
bolts and 4 vanes never worked very well one always ends up in front
of a vane, never mind the confusion when adjusting it).
VANE WIDTH = 3/4" wide
by .024" thick steel, for 8" to 12" mirrors.
1 1/4" wide by .030" thick steel, for 13" to 20' mirrors.
VANE CLEARANCE = 1/8" before tube
CENTRAL CROSS PIECES = rectangular aluminum extrusion cross pieces, using the
least amount of mass to accomplish the task ( no heavy, heat dissipating
central hub ). They are ultra light and ultra rigid.
DIAGONAL OFFSET = is incorporated right into the aluminum cross pieces
( something that was never possible in commercial spiders ).
only be accomplished through PayPal
also include your
email me with your address so I can
add the shipping costs and give you a total
your specs. tube id., your diagonal size, mirror dia.
and your F ratio
Note: All Spiders are #4 vane configuration and come
with Diagonal Holder
Spiders for 8" to 10" mirrors = $82.00
Spiders for 12" to 14" mirrors = $99.00 Can.
Spiders for 15" to 20" mirrors =
If you would like to see some examples of my ATM work from the past 20
years go to my
Main Page -
The Gary Wolanski Projects
Back to Gary's