B Why do pictures of stars have 4 cardinal points?

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Pictures of stars often display four cardinal points, known as diffraction spikes, which are caused by the internal support structure of telescopes, particularly those with spider vanes. The number of spikes can vary depending on the design of the telescope, with some configurations allowing for six or even eight spikes. Bright stars produce more pronounced spikes, while fainter stars may not show them due to lower contrast against the background. The spikes help distinguish point sources like stars from extended sources such as planets or galaxies. Overall, diffraction spikes are a common optical phenomenon in astrophotography, influenced by the telescope's design and the brightness of the observed stars.
  • #31
Yes the spikes are produced before the image gets saturated, but the final result is an extended image which could be confused for a potential cluster member if it wasn't for the spikes...
 
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  • #32
pinball1970 said:
Top of pops was the usual one as there were always visible studio lights.
The rays in the TV camera images are caused by internal reflection/diffraction off of the lens's iris. Closely related to the telescope images, but of course there are no mirror supports in the TV camera.
 
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  • #33
James Demers said:
The rays in the TV camera images are caused by internal reflection/diffraction off of the lens's iris. Closely related to the telescope images, but of course there are no mirror supports in the TV camera.
Thanks the guys gave a few examples, I always liked them (spikes) in older 1970s studio shows
 
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  • #34
Astro telescopes do not have adjustable apertures so the whole length of the optical assembly is circular cross section. That minimizes diffraction effects. Smaller aperture scopes use lenses sothere’s No need for a web to hold a secondary mirror.
 

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