Looking at astro images, I noticed that the stars always have this "+" shaped flares. What is this due to? Is it the same for SCT, MCT, Newtonians and refractors? Why doesn't the star have other shapes like 8 flares, etc?
curious
rich
Why Stars Images have Flaring/Spikes?
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Airconvent
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Why Stars Images have Flaring/Spikes?
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weixing
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Hi,
The "+" shaped flares are the diffraction spikes cause by the support or the vane spider that hold secondary-mirror bracket.... so only reflecting telescope that use vane to support the secondary mirror will have it, such as Newtonian. So MCT, SCT, Refractor and some reflector that don't use a vane to support the secondary mirror(such as Samuel INTES-MICRO MN56) won't have the diffraction spikes.
Basically, each vane causes two spikes, perpendicular to the vane, so 2-vane spider and 4-vane spider cause 4 visible spikes. Some ATM spider use a curved-vane spider will spread the diffracted light throughout the field, eliminating the spikes... but I haven't seen through one yet.
By the way, if I remember correctly, I don't see any diffraction spikes in my newtonian... may be I didn't notices it or my aperture is not large enough. But I saw the diffraction spikes before in the Takahashi Mewlon 180 on one of the observation session with Remus.
Have a nice day.
The "+" shaped flares are the diffraction spikes cause by the support or the vane spider that hold secondary-mirror bracket.... so only reflecting telescope that use vane to support the secondary mirror will have it, such as Newtonian. So MCT, SCT, Refractor and some reflector that don't use a vane to support the secondary mirror(such as Samuel INTES-MICRO MN56) won't have the diffraction spikes.
Basically, each vane causes two spikes, perpendicular to the vane, so 2-vane spider and 4-vane spider cause 4 visible spikes. Some ATM spider use a curved-vane spider will spread the diffracted light throughout the field, eliminating the spikes... but I haven't seen through one yet.
By the way, if I remember correctly, I don't see any diffraction spikes in my newtonian... may be I didn't notices it or my aperture is not large enough. But I saw the diffraction spikes before in the Takahashi Mewlon 180 on one of the observation session with Remus.
Have a nice day.
Yang Weixing
"The universe is composed mainly of hydrogen and ignorance."
"The universe is composed mainly of hydrogen and ignorance." 
Hi Wei Xing,weixing wrote:Hi,
ATM spider use a curved-vane spider will spread the diffracted light throughout the field, eliminating the spikes... but I haven't seen through one yet.
By the way, if I remember correctly, I don't see any diffraction spikes in my newtonian... may be I didn't notices it or my aperture is not large enough.
Have a nice day.
My home-made truss dob has curved spiders and it does eliminate the spikes nicely. You can make one too using a stiff steel ruler like what I did.
You will not see any diffraction spikes in your newt if the object is not bright enough. You should see it if you look at objects like Sirius, Venus, Mars (during Marswatch), Jupiter etc. I saw a prominent spikes on Mars through the Portaball during Marswatch.
Slightly dimmer stars also have spikes, but these spikes are dim and can only be caught in a long-exposure shot.
Kay Heem
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tanguan2001
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Wei Xing,
We have the same scope, I think. On mine, I actually use the spikes to help with focussing on CCD. Aim at a bright star, take a few seconds exposure and the spikes are visible. Focus until the spikes are nice and sharp.
By the way I think the spikes are aesthetically quite pleasing. I have seen astropohotos where the imager has made spikes with thin rods across the objective.
TG
We have the same scope, I think. On mine, I actually use the spikes to help with focussing on CCD. Aim at a bright star, take a few seconds exposure and the spikes are visible. Focus until the spikes are nice and sharp.
By the way I think the spikes are aesthetically quite pleasing. I have seen astropohotos where the imager has made spikes with thin rods across the objective.
TG