[avandonk]

Greg the diffraction spikes around the bright star are produced by non uniform edges of the metal holding your optic elements. It usually is a mixture of specular reflection and diffraction. Any diffuse reflections will lower the overall contrast.

If you get an aperture laser cut that is a few mm smaller than the entrance aperture of the scope and mount it in front the bright stars will be far cleaner.

Even though this is a tiny fraction of the incident light as sensors and filters get better it then rears its ugly spikyness.

To test this just cut an aperture out of black card or paper and take a few test exposures of very bright stars.

It is about time that top telescope makers put an exterior baffle or aperture to eliminate any light hitting the edges of the element holders.

The basic rule is to eliminate any light not contributing to the image before it enters your optical train.

I use an exterior aperture on the 300mm lens and an extended dew shield. The lens only 'sees' an area of sky just a bit bigger than the area being imaged. The increase in contrast is quite noticeable and is the difference that gives detail in dim dust. This is because a lens is not as well internally baffled as a high quality APO. Any off axis light that is not from the area being imaged gets scattered inside the lens and lowers contrast.

Bert