Spider Vane choice

[norm]

Hi All,

Can someone advise what are the pros/cons to choosing either a 3, 4 or curved spider vane. (the curved type will most likely be a 180 degree type, not 60 degree).

I don't mind diffraction spikes but then again, I haven't really given them much thought. Are views different or neglible. Does one design give better views to the other, or does it boil down to personal preference ?
I prefer sharp/tack views and splitting doubles/multiples is something I'd like to get into, outside of DSOs and planetary stuff.

From what I have read a 60 degree curved spider vane seems to be the choice, but I don't think its an option.

Outside of what I have read on the net, comments and experience really appreciated.

PS: scope is an SDM 14" f4.8 WIP.

Cheers,

Norm

[Ian Robinson]

I'd err on the concervative side and go for either a 4 vane standard spider or curved spider because this will give a more rigid unit.

[Alchemy]

Q... are curved spiders comercially available, or is it the home made kit.

i suspect you are a visual person, but from experience the diffraction spikes make processing images a pain. (stars go square if you shrink them)

[gb_astro]

Have you read this one?

http://www.telescope-optics.net/spider.htm

gb.

[norm]

Hi GB, yes I have. The scope will be purely visual and the curved spider will most likely be commercially made, eg Protostar.

:shrug:

Cheers,

Norm

[Satchmo]

The best design is 3 vane each vane subtending a 60 degree arc. Protostar does make curved spiders but to their own design which may not be optimal, but still better than seeing 4 or six spikes on bright stars and planets.
You might want to check out these guys who make something closer to the correct design :
http://www.1800destiny.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=1D&Category_Code=CVS

Curved spiders can be just as rigid as there is a fair bit of strength in bending it . If you are making one, make the vanes from 2mm steel. Thicker vanes are still not thick enough to lower contrast they just create a little more diffraction, which Is spread evenly over the whole field and not perceptible.

Dick Suiter showed the contrast transfer function ( MTF) of a scope was not significantly effected as long as the vane thckness was kept below 1/128 of the aperture in mm.

Hope this helps.

[norm]

Hi Mark,

Thanks for the link. If I went the curved spider, I'd being going the 3 vane type at 60degrees....

Cheers,

Norm