Eyepiece for refractor telescope

  • Context: Stargazing 
  • Thread starter Thread starter PhysicoRaj
  • Start date Start date
  • Tags Tags
    Telescope
Click For Summary

Discussion Overview

The discussion centers around the construction of a refractor telescope, specifically focusing on the selection of an appropriate eyepiece to pair with a biconvex lens being considered as the objective. Participants explore various configurations and considerations for achieving desired magnification and image quality.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant proposes using a biconvex lens with a 27 cm focal length as the objective for their telescope.
  • Another participant suggests that to view the rings of Saturn, a short focal length eyepiece may be necessary, possibly in conjunction with a Barlow lens.
  • A request for specific recommendations on eyepiece focal length and diameter is made, indicating a desire for guidance on configuration.
  • A participant explains that the ratio of the objective and eyepiece focal lengths determines magnification, emphasizing that shorter eyepiece focal lengths yield greater magnification.
  • It is noted that using a negative (concave) lens for the eyepiece is less effective than a positive lens for viewing through the telescope.
  • One participant describes a common refractor design, suggesting a 100 mm doublet lens with a focal length of 1000 mm and recommending specific eyepiece focal lengths for various magnifications.
  • Another participant advises seeking resources on telescope building and connecting with amateur astronomer clubs for additional support.

Areas of Agreement / Disagreement

Participants express differing views on the optimal eyepiece configuration and the effectiveness of various lens types, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Participants acknowledge that their analyses may overlook potential aberrations and other complexities involved in telescope design.

PhysicoRaj
Gold Member
Messages
538
Reaction score
49
Hi, Iam thinking of making my own telescope and I have a magnifying glass lens, biconvex, about 10 cm in diameter and 27 cm focal length. I think it would be better as the objective. For the eyepiece, what type of lens, of what focal length and aperture diameter should I use? (I hope to identify the rings of Saturn... I may not be able to .. but at least the craters of the moon are okay.)
Thanks.
 
Astronomy news on Phys.org
The rings of Saturn are a piece of cake, but with that short focal length, you'll need a short focal length eyepiece and maybe a Barlow.
 
Then what type of a configuration you suggest(focal length combination and size)? May be I will try to get both new, the eyepiece and the objective.
 
PhysicoRaj said:
Hi, Iam thinking of making my own telescope and I have a magnifying glass lens, biconvex, about 10 cm in diameter and 27 cm focal length. I think it would be better as the objective. For the eyepiece, what type of lens, of what focal length and aperture diameter should I use? (I hope to identify the rings of Saturn... I may not be able to .. but at least the craters of the moon are okay.)
Thanks.

The ratio of the objective and eyepiece focal lengths provides the (angular) magnification, so the shorter the focal length of the eyepiece, the greater the magnification. Using a negative (concave) lens for the eyepiece is worse than a positive lens when you are trying to look through the telescope (see Galilean vs. Keplerian telescopes).

http://depts.washington.edu/hssexec/committee/hss_galileo.html

The f/# of your objective is 2.7, so the f-number of your eyepiece does not need to be much larger than 2.7 as well.

This simple analysis completely ignores aberrations, which are likely to be large.
 
A common simple refractor design is a 100 mm doublett lens with a focal length of 1000 mm. For maximum FoV you'd need a 50 mm eyepice. Together with a 2xbarlow lens and a second eyepiece around 12 mm. This way you'd get magnifications of 20, 40, 83 and 167.

I'd recommend that you start by getting your hands on a book on building telescopes and checking if there is an amateur astronomer club nearby. There are a lot of gotchas if you haven't built a telescope before.
 
Thanks a lot...
 

Similar threads

Stargazing Calculating the Resolving power of a Telescope
  • · Replies 7 ·
Replies
7
Views
4K
Stargazing Level of details in prime focus vs eyepiece images
  • · Replies 226 ·
8
Replies
226
Views
17K
Stargazing Telescope Design: Calculating Total Distance from Primary Mirror to Eyepiece
  • · Replies 2 ·
Replies
2
Views
2K
Stargazing Worth it to buy 2" eyepieces for Newtonian telescope?
  • · Replies 27 ·
Replies
27
Views
6K
Stargazing Is the INTEY Ultra-Clear Telescope a Good Choice for Beginner Astronomers?
  • · Replies 10 ·
Replies
10
Views
5K
Stargazing Problem in making a small refracting Telescope
  • · Replies 3 ·
Replies
3
Views
4K
Stargazing Celestron Powerseeker 60AZ Telescope
  • · Replies 4 ·
Replies
4
Views
8K
Stargazing A good telescope with tracking for deep sky objects
  • · Replies 17 ·
Replies
17
Views
4K
Stargazing Question on Refractor Telescope
  • · Replies 6 ·
Replies
6
Views
5K
Stargazing How Do I Choose the Right Optical Lenses for Building a Telescope?
  • · Replies 4 ·
Replies
4
Views
3K