I can accept being wrong, but only if I learn something. :D Josh On Tue, Mar 6, 2012 at 7:54 PM, Chuck Hards <chuck.hards@gmail.com> wrote:
Excellent points, Brent, and well worth repeating. In fact a curved vane spider actually INCREASES overall diffraction due to the longer vane in the light path. As you note, the overall scattered light is distrubuted over a larger area- this means decreased contrast, but the absence of an obvious visible spike fools our brain into thinking we have better contrast and a better view. More aesthetically pleasing- to some- but not intrinsically better.
Diffraction spikes can be used as an observing tool, escpecially if you like close, unequal double stars. By rotating the OTA, you can place the dim companion between the spikes and increase it's visibility. That's because the spikes are drawing energy away from the main diffraction rings around the brighter companion, and increasing contrast closer to it. Result: The companion is more visible.
Even the best-made refractors have diffraction rings, it's a property of light and we can't do anything about it. Being a lifetime Newtonain user primarily, I've learned to live with spikes, and use them to my advantage when needed.
On Tue, Mar 6, 2012 at 4:38 PM, Brent Watson <brentjwatson@yahoo.com> wrote:
I failed to mention that the diffraction caused by a spider is not eliminated by a curved vane. It is only minimized visually. The curved vane does affect resolution, especially if it is thick. Visually you don't see it as much because the angle of the vane changes constantly as a function of its position in the aperture. This makes the spike seem to dissappear, but its effects are still there.
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