Eyepiece for refractor telescope

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In summary, a 10 cm diameter biconvex lens with a focal length of 27 cm and an f/# of 2.7 would be a good eyepiece for looking at the rings of Saturn. You would also need a short focal length eyepiece and a Barlow for maximum magnification.
  • #1
PhysicoRaj
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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.
 
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  • #2
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.
 
  • #3
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.
 
  • #4
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.
 
  • #5
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.
 
  • #6
Thanks a lot...
 

1. What is an eyepiece and what does it do?

An eyepiece is a small lens that is placed at the end of a refractor telescope. It is responsible for magnifying the image of the object being observed, allowing you to see it more clearly and in greater detail.

2. How do I choose the right eyepiece for my refractor telescope?

The right eyepiece for your refractor telescope will depend on several factors, including the focal length of your telescope, the magnification power you desire, and the type of objects you want to observe. It is best to consult with a knowledgeable telescope dealer or do some research online to find the best match for your specific telescope.

3. Can I use any eyepiece with my refractor telescope?

No, not all eyepieces are compatible with all refractor telescopes. It is important to check the specifications of both your telescope and the eyepiece before purchasing. Some telescopes may require specific types or sizes of eyepieces, so it is best to check with the manufacturer or a reputable dealer before making a purchase.

4. How can I clean my eyepiece without damaging it?

To clean your eyepiece, use a soft, lint-free cloth and gently wipe away any dirt or debris. It is important not to use any harsh chemicals or abrasive materials, as they can scratch or damage the lens. If there are stubborn smudges or marks, you can use a small amount of lens cleaner specifically designed for optical lenses.

5. Can I use multiple eyepieces with my refractor telescope?

Yes, you can use multiple eyepieces with your refractor telescope. This allows you to have a range of magnification options for different objects and viewing conditions. It is important to have a good selection of eyepieces for optimal viewing experience, but be mindful not to overload your telescope's carrying capacity.

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