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spider defraction spikes

Started by Sean Cunneen, 07/20/2007 05:50PM
Posted 07/20/2007 05:50PM Opening Post
I am new to reflectors, I've had refractors all my life. I've just purchased a 6" f/8 I'd like to use just for planetary. I have been reading about spiders and 3 vane vs 4, curved vs straight. My question; does the thickness of the vanes affect the quality of the diffraction spikes? My telescope comes with threaded rod vanes about 3/32"dia, what if I replaced those with rods 1/16"dia, or take it to an extreme, suspending the secondary with music wire under tension. If the diffraction spikes are ot all that effected by thickness of the vane, it may not be worth the effort. Anyone have any experience? Thanks in advance,

Sean Cunneen
8" f/8 homebuilt on CG-5 GEM
22 Pan
12 T4
TMB 7mm
TMB 5mm
TMB 3.2mm
Posted 07/22/2007 10:22AM #1
A good supplier of custom spiders is
Posted 07/26/2007 09:42PM #2
Hi Sean, I agree with Dave about the diffraction spikes for planetary viewing. You will get a smaller spike from a thinner vane but do be carefull that the secondary is well supported and stays collimated. Contast and Collimation are the key with planetary views. I saw a link for an apodizing mask I think in this forum which fits over the spider vanes and is supposed to minimize the spikes. I have a hard copy I can scan and email if you like. I have not tried it but it looks easy. Best improvements I made on my 8 inch F6.25 for planetary viewing was flocking the tube and getting a good observing chair.

Clear skies
Dave H.
Posted 07/26/2007 11:44PM #3
You could buy a curved spider to replace the original one and the spikes will be gone.
Or you could replace the spider with a thin bladed straight one and reduce the spikes.

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