1800 Destiny Curved Vane
Newtonian Spiders
Hans Wiest — +001 925 846 4200 — $50-300
If you find the diffraction spikes surrounding bright objects in
your Newtonian annoying, you're not the only one — I find them
positively irritating and consider that they should only be seen
adorning stars on Christmas cards. So what's the answer? Well, if
you modify the design of your spider such that the arms supporting
the secondary mirror are curved, then the diffraction is spread
around the image instead of being concentrated into a linear
pattern.
Various forms of curved spider will work, but one configuration
that works particularly well is to have three vanes spaced at 120°
intervals, with the portion of the curved vane that is imposed on
the mirror making a 60° arc. Since a spider vane produces a
symmetrical pattern on the opposite side of the image (a
traditional cross-shaped spider actually generates an eight-spike
pattern, each reinforcing the diffraction of its opposing member)
whether it's curved or straight, this curved three-vane design
actually spreads the diffraction evenly through a full 360° of the
image. This ensures that you have the minimum interference with
image quality.
One manufacturer who makes curved spiders to this very
specification is
1800 Destiny run by
Hans Wiest in
Pleasanton, California. Hans sells spiders for Newtonians and
Cassegrains of 6-inch aperture and above with holders for 1-inch
secondary mirrors and larger. The units are very well made with
Allen key collimation adjustment and a spring tensioner. They are
also very rigid, the three arms bracing the spider firmly against
the tube wall (you specify your 'scopes internal tube diameter when
ordering) with no discernible vibration. The spiders are also easy
to install (
instructions on the website) with just three
¼-20 mounting holes to drill into your tube. I retrofitted two
'scopes in just one hour.
I replaced the traditional four-vane spider of a
6-inch f/11 OD150L with the smallest model
1800 Destiny currently manufactures. Given that this 'scope
possesses a 1-inch elliptical secondary, the idea was to optimise
this proven planetary performer still further by reducing
diffraction effects to the bare minimum. So how well does it work
in practice? I'll update this entry once I've had further
opportunities to evaluate it, but initial results were every bit as
good as I'd hoped. The waning gibbous disc of Venus seen in bright
twilight no longer sat in a diffuse cross of light. Rather, there
was a far less obtrusive and evenly distributed weak halo of light,
far more like a high-quality apochromatic refractor. Turned toward
Vega later in the evening, poor seeing and scudding cloud proved
frustrating, but the fleeting views were sufficient to reveal that
the experiment had been a success. The views are far more like that
of a high-quality Maksutov with a small secondary obstruction. A
highly recommended upgrade for your Newtonian.
