Offset Spider Vane Assemblies
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
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 ).
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.
= 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).
= 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.
= 1/8" before tube wall.
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.
= is incorporated right into the aluminum cross pieces ( something that
was never possible in commercial spiders ).
Purchasing can only be accomplished
email me with your address so
I can add the shipping costs and give you a total
also include your
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 = $100.00
Spiders for 12" to 14" mirrors = $120.00
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
- The Gary Wolanski Projects
Back to Gary's