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I couldnt resist posting this quote from Alan Adler (us sky and telescope issue jan 2002) a respected contributor to sky and telescope both US and AUS for many years i have enlarged a particularly interesting section relevant to this discussion
The full potential of your Newtonian can be realized with only a small investment of time and money. By Alan Adler interest in thermal management began when S&T associate editor Gary Seronik played me a video made by Bryan Greer that showed heat waves slowing rising from the front surface of a 6-inch mirror. F or years reflecting telescopes have taken a back seat to refractors for high-magnification views of planets and double stars. The reflector's central obstruction is most often blamed for this shortfall. However, a strong body of theoretical and experimental evidence has shown that central obstructions of 15 percent (perhaps even as high as 20 percent) of the diameter of the primary mirror are not visually detectable. Another often-cited scapegoat is surface accuracy. Although errors on reflector optical surfaces must be one-fourth those of refractors to achieve the same results, such accuracy is quite common in good reflectors. So what's holding back well-made reflectors? I am convinced that it is not a central obstruction, and it's not optical quality -- the problem is heat waves off the mirror surface. This layer of warm air behaves like a weak lens of very poor quality right in front of the mirror. I believe this is the main reason reflectors have always been regarded as poor cousins to refractor telescopes. Taking the Heat from Your Mirror Thermal management in your reflecting telescope can yield astonishing improvements in resolution and contrast.
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