Curved spiders?

[estwing]

can anyone tell me why people have these on bigger dobs? is there an advantage to this shape?

[wookie1965]

http://webstertelescopes.com/frequently_asked_questions.htm

Have a read of this the question is further down about curved spider veins i think this will answer your question.

[JamesF]

The spider causes diffraction of the light entering the OTA. When the spider vanes are straight the diffraction effects reinforce each other and you get diffraction spikes appearing in the image. Having curved spider vanes prevents the reinforcing effect so the spikes don't show up. The negative side is tht because the vanes are longer more diffraction actually happens, but because it's spread out it tends not to be visible.

James

[Moonshane]

I agree with the above but suspect it may be structural too. at larger apertures, the thinner vanes may be more likely to twist with the weight of the secondary and there are a few options to correct this - deeper vanes, thicker vanes and curved vanes.

I don't mind diffraction spikes myself.

[John]

My new-to-me Orion Optics 12" newtonian has curved secondary supports. When I get first light with it I'll find out what effect they have. All the newts I've used to date had the 4 straight vanes with the exception of a mak-newt which used a glass meniscus to support a very small secondary.

From what I've read I'm expecting diffraction to still be present but not in the form of spikes. We will see

[estwing]

every time i ask a question,looking for simple answer...

[Moonshane]

I think we all go through this when looking for larger aperture. nothing is as simple as when you first start looking. I was going through the same thing when a 16" f4 0.984 strehl mirror came up for sale used at a great price, taking away need for further debate and though. I think sometimes large aperture spiders are made curved as this is easier to do in some ways than a cross, or at least accuracy is more critical with the cross.