Hans Wiest — +001 925 846 4200 — were $50-300
Written: ~5 years ago
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.