Spider Vane upgrade

[nitram100]

Hi,

I'm going to be upgrading my friends spider vane in his telescope, he currently has the same scope as me, an Orion Optics 10" F4.8 Newt.

The existing spider vane is a very thick single vane affair, which i'm sure older OO owners are familair with. I recently upgraded my scope to a 4 vane spider from Orion Optics and am happy with it, but it now appears he has the choice of a 4 vane or a double circle spider, like the one below.

http://www.cloudynights.com/images/spx2.jpg

Has anyone had any experience with these double O spiders? Are they better than the traditional 4 vane?

Thanks for any advice!

[beetlejuice]

I have a 'double o' spider on my home-built 6" newt. It definitely works better than a standard straight vane spider with with no sign of spikes at reasonable magnifications. The 'star' shaped spikes formed by straight-vane spiders are a result of each vane slightly interfering with the passage of light causing diffraction. The diffraction effects are increased with straight-vane spiders as opposing vanes reinforce the effect of each individual vane. Curved spiders on the otherhand spread the diffraction effect over a larger area of the mirror and thus the visual impact is greatly reduced. So I would say 'go for it'.

[johninderby]

Circular/curved vanes do however reduce contrast, so as to which is better depends on what you are observing. For DSOs where contrast isn't so important the circular/curved type would be better but on lunar/planetary etc. where contrast is important the straight 4 vane type is better.

John

[nitram100]

Thanks alot for the info guys!

Well, considering that the planetary performance on the F4.8 scope isn't very good as it stands, a drop in contrast could make it alot worse.

Do you think the contrast drop would be very noticeable? I could get the OO spider and flock his scope to try and make up a tiny bit of the lost contrast.

[johninderby]

It would be just a few percent drop in contrast. Flocking would help regain part of it so the curved vanes with flocking wouldn't hurt contrast that much. Of course straight vanes and flocking................

It' s really only important when you're trying to get every last bit of planetary performance out of your scope.

John

P.S.

Google Protostar flocking