Well, it's time to hire Mythbusters to settle this. Maybe its both. If the struts were that big of a problem, then couldn't they use a flat lens-plate(s) to hold the secondary mirror instead?
Astronomers hate putting lenses into their optical systems--there is always some light lost to reflection off the glass surface. The VLT is an 8 meter diameter telescope, so supporting a giant lens above the telescope would be a major engineering issue. This isn't really a problem you can solve by adding a new lens or tweaking the secondary support structure--it's a fundamental feature caused by the wave nature of light. Anytime light passes through an aperture, it creates a diffraction pattern.
Why do star photos have crosses over bigger stars?
Refraction flares caused by the crystalline pattern of molecules in the glass of the lenses.
Um, no. The spikes are caused by the diffraction of light around the struts supporting the secondary mirror in the telescope. The wave nature of light ensures that no matter how large you build your telescope, you cannot focues stars to a perfect point.
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