Spider free mount for secondary mirror

  • Context: High School 
  • Thread starter Thread starter vincentm
  • Start date Start date
  • Tags Tags
    Mirror
Click For Summary

Discussion Overview

The discussion revolves around the design and implementation of spider-free mounts for secondary mirrors in telescopes, focusing on methods to minimize diffraction and improve optical performance. Participants explore various approaches, materials, and designs, including curved spider arms and alternative mounting techniques.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants inquire about available kits for spider-free mounts to reduce diffraction.
  • There is a suggestion to use a sheet of plane glass as an alternative mounting method, although concerns about introducing additional air-glass surfaces are raised.
  • Curved spider arms are proposed as a solution to reduce distinct diffraction spikes, with claims that they spread diffracted light over a larger area, making it fainter.
  • Participants discuss the trade-offs between using curved versus straight spider arms, noting that curved arms may lead to poorer signal-to-noise ratios but clearer views for naked-eye observations.
  • One participant mentions the possibility of selling a current telescope for a Catadioptric model, which features a correcting lens for the secondary mirror.
  • Interest in off-axis mirror designs is expressed, highlighting their potential for superior views but noting the challenges in construction.

Areas of Agreement / Disagreement

Participants express various opinions on the effectiveness of different mounting techniques and the implications of using curved versus straight spider arms. No consensus is reached on the best approach, as multiple competing views remain.

Contextual Notes

Participants mention specific materials and techniques, such as using hacksaw blades for curved arms, but do not provide detailed specifications or confirm the feasibility of all proposed methods.

Who May Find This Useful

Amateur telescope makers, enthusiasts interested in optical design, and those exploring advanced telescope mounting techniques may find this discussion relevant.

vincentm
Messages
322
Reaction score
3
Is there any kits i can purchase? I'd like to avoid diffraction as much as possible.
 
Astronomy news on Phys.org
The only alternative (except possibly magnetic leviation) would be to stick it on a sheet of plane glass.
 
mgb_phys said:
The only alternative (except possibly magnetic leviation) would be to stick it on a sheet of plane glass.

See, that's what i'd like to do, but where would i be able to purchase the rings to keep it in place?
 
Your best bet is to look into a spider with smoothly curved arms. If you fastened a secondary to an optical flat, you would introduce two more air-glass surfaces and decrease the contrast of your scope. Curve-arm spiders have been in use for many years.
 
turbo-1 said:
Your best bet is to look into a spider with smoothly curved arms. If you fastened a secondary to an optical flat, you would introduce two more air-glass surfaces and decrease the contrast of your scope. Curve-arm spiders have been in use for many years.

Ok, that makes sense turbo, I've purchased all the parts in order to make mine curved (hack saw blades via the scopemaking.net guide), i was just curious about pursuing this route.
 
What's the advantage of using a curved spider arm over a straight one?
 
tony873004 said:
What's the advantage of using a curved spider arm over a straight one?

The difraction spikes instead of being distinct crosses around each star will be smeared out. Since each point in the spider will create a weaker diffraction spike at a different rotation angle.

Overall it's poorer signal to noise, but it looks clearer for naked eye observations.
 
Curved arms would spread the diffracted light through different angles (i.e. a larger area), making it fainter. A straight edge "bends" the light in one direction only, hence the bright, directional diffraction spikes that are common with straight-edge spiders.
 
mgb_phys said:
The only alternative (except possibly magnetic leviation) would be to stick it on a sheet of plane glass.

Or sell your current telescope and buy a Catadioptric telescope which has a weak, correcting front lens on which the secondary is mounted.
 
  • #10
I've been intrigued by off axis mirror designs for a number of years. They are capable of views rivaling, or even surpassing the finest refractors. Unfortunately they are difficult to make and have existed only among the ranks of the most ambitious and gifted amateur telescope makers until fairly recently Some commercial models are now available - e.g., http://users.erols.com/dgmoptics/indexwelcome
 

Similar threads

High School More scope refurbishments or start new?
  • · Replies 7 ·
Replies
7
Views
2K
High School What If We Could See the Past by Placing a Mirror on the Sun?
  • · Replies 13 ·
Replies
13
Views
3K
Stargazing Setting up first telescope - need advice
  • · Replies 9 ·
Replies
9
Views
2K
Stargazing What's the Best Telescope for Astrophotography Under $1,500?
  • · Replies 25 ·
Replies
25
Views
5K
High School What can I expect to see with a 6inch mirror?
  • · Replies 4 ·
Replies
4
Views
1K
Stargazing Dust on the Mirror: Is Cleaning Worth the Risk?
  • · Replies 19 ·
Replies
19
Views
4K
High School Help w/ repairing/refurbishing an equatorial mount
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad Understanding magnification of concave mirrors for near-eye situation?
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad Fabry-Perot Interferometer mirrors
  • · Replies 7 ·
Replies
7
Views
5K
Secondary Mirror in Solar Concentrator Dish Designs
  • · Replies 6 ·
Replies
6
Views
4K