Telescope Vane Spiders and Holders

The spider vane in your telescope is the word enemy you have. Most mirrors are pyrex or better glasses that will not deform over a reasonable temperature range. The spider on the other hand is always there in front of the field of view. Unless you use offaxis telescope mirrors you are stuck with the diffraction and light loss of your spider.

Below are spider pictures. Is there really a best spider. Yes and No!!

Your best standard is the SINGLE VANE SPIDER

Low diffraction and low light loss spider for 6"f12 scope.

When you need both Cassigraian and a Flat Diagonal

Build a Single Vane spider and Flip IT !!!

The 4 vane spider is the worst enemy of all telescopes, big and small. If your telescope is less than 8" diameter so your tube is about 10" in inner diameter you can use the SINGLE VANE spider. The strait across single vane spider will reduce the diffraction in one direction to none. Any spider that is curved or has 3 or 4 or more vanes is gonna cause you serious diffraction and light loss if you try to view at high power and double stars.

Think SINGLE VANE for all sizes.

Any combination of curved, bent, out of plane spider vanes cause smearing of the image by diffraction effects.

There are many articles on the diffraction effects caused by telescope spider vanes. See the following articles to decide your choice for your telescope.

web sites that talk about spider vane diffraction and telescope resolution.

1. http://www.starizona.com/aboutus/diffraction1.pdf

Users of reflecting telescopes that have vane-supported secondary mirrors are well aware of the connection between the vanes and the diffraction spikes that appear extending from images in the eyepiece. Few, however, understand why the spikes occur or what the geometric relationship is between the spikes and the vanes. Even fewer understand the relationship between an obscuring shape and the diffraction pattern resulting at the focus. The purpose of this paper is to make an explanation without delving into the mathematics of diffraction theory. The diagram above will provide assistance, and we’ll begin there naming parts.

2. http://24.237.160.4/files/Astronomy/ATM%20stuff/Spiders.PDF

All about curved spiders and there search light scatter effects.

3. http://www.atmsite.org/contrib/Carlin/spider/

This hack saw type has OFF CENTER spiders that will cause terrible diffraction effects.

4. http://www.mso.anu.edu.au/nifs/sdns/sdn0005.06.htm#_Toc479560826

Here is a study on telescope diffraction effects.

5.

3 curved vanes spider.

This is about as bad as they get in diffraction smearing.

Single Long Curved Vane Spider

Note the wide vane blocks light. The curved vane smears the diffraction over the whole image.

Here is the classic 4 Vane crossed spider

The vanes are small and sometimes thin wire is used. But you don't get rid of the diffraction.

Here is an 8 wire off set spider setup.

Note low light loss but off axis you have 8 diffraction wires.