What causes those spikes in star images?

[Daveskywill]

Hello:

I was wondering if it's possible (because I think it is) for a refractor or Schmitt-Cassegrain to exibit those spikes on star images.

Like typically there are 4 at opposite (90 degree) places.

I used to think that those are because of spider vains in the scopes secondary holder.

But now I'm not sure.

Can anyone tell?
Thank you.
David

[Poita]

It is caused by the spider vanes. Though I know people have put thin crossed string in from of their refractors to get the same effect.

[iceman]

Hi David

Yes - the spikes are from the spider veins in newtonians.

On refractors or SCT's, if images have star spikes it's usually due to either:

a) A piece of fishing line or similar strung across the front of the objective in a X pattern

b) Introduced artificial spikes during processing using one of the many tools available

[Poita]

Heh heh, 3 posts, three different spellings of vanes. Aint the English language a wonderful beast.:lol:

I'll have to try the fishing line trick, it could be fun to mess with it for terrestrial night shots too.