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11 votes
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What does par. lines mean in relation to a telescope aperture in 19th century German astronomical publications?

I think it means a Paris line, or ligne. In Klinkerfues (1867) it seems the author uses Paris inches, which was a common unit in particular for lenses. One Paris inch is equal to 1.0657 "modern&...
pela's user avatar
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10 votes

For lenses, what is the practical difference between plano- and bi-?

I don't know if this is a trivially obvious question for astronomers... Astronomers (amateur, pro, or otherwise) are a diverse bunch; some are intimately involved in telescope and instrument design, ...
uhoh's user avatar
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9 votes
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What was the largest telescope ever fitted with an eyepiece

A recent Twitter thread included a post by someone who had looked through an eyepiece on the 8.2 meter Melipal ("UT3") telescope of the ESO VLT. Here's the original post: Astro friends: anyone ...
Daniel Griscom's user avatar
9 votes

Would a telescope that uses Fresnel lenses be more practical than using regular lenses?

The main advantage of a Fresnel lens is its reduced mass compared to a normal lens. Its disadvantages include difficulty of manufacture and diffraction from the discontinuities in the aperture, these ...
Conrad Turner's user avatar
7 votes

Constructing a periscope/telescope - trouble with lenses

You're close! What you built is a back-to-back set of Galilean telescopes (with an overall magnification of 1:1). The reason you're getting a smaller circle, but with a life-size image, is that the ...
nflemming2004's user avatar
6 votes

How is it ensured that a parabolic shape forms while polishing a telescope mirror?

How is it ensured that a parabolic shape forms while polishing a telescope mirror? While a spherical shape is fairly easy to abtain, a parabolic shape definitely isn't! It's a combination of special ...
Florin Andrei's user avatar
6 votes

Can a telescope image be amplified to see more by adding distant lenses or mirrors?

Speaking in general, telescopes are designed as complete systems from the beginning. It's not generally feasible to improve performance by just adding yet another lens or mirror to the assembly. The ...
Florin Andrei's user avatar
6 votes

Relation between angular resolution and aperture?

Your formula is correct. In the absence of instrumental effects or blurring of the atmosphere, it gives (approximately) the minimum angular separation between two objects that can be resolved. The ...
ProfRob's user avatar
  • 153k
6 votes

Relation between angular resolution and aperture?

The angular resolution only tells you your ability to distinguish ("resolve") two separate points of light. For example, your ability to distinguish the two distinct headlamps on a car from being a ...
zh1's user avatar
  • 161
5 votes
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How can I find out the maximum magnification of my telescope?

The magnification is given by (focal length of telescope)/(focal length of eyepiece). The spec I saw said the telescope focal length is 800mm, and the maximum magnification is 160x, so to get that ...
Dr Chuck's user avatar
  • 4,349
5 votes

Would a telescope that uses Fresnel lenses be more practical than using regular lenses?

It is interesting, it looks like you can combine a "normal" lens with a fresnel to correct for chromatic abberation and have a lighter lens. I don't think it helps with making a bigger refractor ...
Russell's user avatar
  • 51
5 votes

Telescope focal point and inversion

The main mirror of a telescope forms an image at the prime focus. You see the lines being brought to a single point, but that doesn't mean all the light entering the telescope is focused to a single ...
James K's user avatar
  • 123k
5 votes

How to choose eyepieces and other accessories for a Celestron 70mm f/5.7 portable refractor?

To your scope the 165x maximum obtainable magnification mentioned by the manufacturer is bit optimistic. However I would recommend you to get 4mm Plossl eyepiece which will give you 133x magnificafion ...
Kavin Ishwaran's user avatar
4 votes

Would a telescope that uses Fresnel lenses be more practical than using regular lenses?

In addition to the diffraction issues pointed out by Conrad Turner, a Fresnel lens would suffer from all the other problems that large lenses in telescopes suffer from: Chromatic aberration ...
Peter Erwin's user avatar
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4 votes
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What is the next lens I should buy?

It's a pretty common tendency to fix problems by buying more eyepieces, but that's rarely how it works in practice. There are a few steps you need to take before buying more glass. Collimation Check ...
Florin Andrei's user avatar
4 votes
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Can a telescope image be amplified to see more by adding distant lenses or mirrors?

Far from "orbit" some of the longest telescopes in history are: Tubed: "Hevelius' Longest Telescope from Machinae Coelestis" - 150 feet Tubeless: "Huygen's Telescope" - 210 feet Apparently Adrian ...
Rob's user avatar
  • 2,656
4 votes
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What's the cheapest lens to buy for showing ISS to a flat earther?

I think you'd want a focal length of 700-1000 mm, and the cheapest way to get that would be a basic Newtonian reflector of 100 mm aperture. Examples: Meade Polaris 114mm, Celestron PowerSeeker 114EQ, ...
Mike G's user avatar
  • 18.7k
4 votes

Not Able to View Objects with Barlow Lens

There are some rules of thumb when it comes to telescopes and usable magnification. One is that your maximum usable magnification is two times the diameter of your telescope's aperture in millimetres (...
Aaron F's user avatar
  • 1,670
4 votes

How to choose eyepieces and other accessories for a Celestron 70mm f/5.7 portable refractor?

Adding a 2x Barlow is almost always recommended regardless of the telescope. This essentially doubles the number of eyepieces you have. They also make looking through a 10mm with a 2x Barlow more ...
Greg Miller's user avatar
  • 5,922
4 votes

Is there a reflecting telescope like as a Newtonian telescope but with a negative lens before the diagonal mirror?

Yes! Those with a Coudé focus and others The following this answer to Why aren't reflector telescopes built with an offset secondary mirror? this answer to Do telescopes exist that reflect the ...
uhoh's user avatar
  • 30.7k
3 votes
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What are some formulas that are associated with the Schmidt corrector?

The specific purpose of a Schmidt Corrector plate is to have an equal but opposite spherical aberration to the primary mirror they compensate for. So any formula you try to come up with will depend on ...
Rory Alsop's user avatar
  • 5,112
3 votes
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Need help in creating telescope

If F is the focal length of the objective, and f the focal length of the ocular, then the magnification of the instrument is: M = F / f So you'll get 10x with the first combination. This is enough ...
Florin Andrei's user avatar
3 votes
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In a reflecting telescope (Cassegrain), is there a difference between using a concave or convex secondary mirror?

There are many flavors of reflecting telescopes based on the original Cassegrain design which has been attributed by history to Laurent Cassegrain: The Cassegrain reflector is named after a ...
uhoh's user avatar
  • 30.7k
3 votes

Would a telescope that uses Fresnel lenses be more practical than using regular lenses?

A group at LLNL have worked on it with DARPA funding. They had a folding glass system called Eyeglass in 2003 and a flexible membrane system called MOIRE in 2013. They embraced the diffraction and put ...
Mike G's user avatar
  • 18.7k
3 votes
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What soviet telescope is this?

Possible search terms to use: Vintage Russian CCCP Spotting Scope 3PT-460 20x Komz Russian Military Telescope - 3PT-460 20x ZRT 460 Russian Scope Images of item: Prices I found range from \$50 to ...
Rob's user avatar
  • 2,656
3 votes

What soviet telescope is this?

Pervomaisk Machine-Building Plant. Portable tripod. Price: 4 rubles 20 kopecks. Portable tripod is designed for lightweight movie cameras and cameras for various kinds of shooting. Spotting scope. ...
A. Rumlin's user avatar
  • 236
3 votes
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Difference between first (focal length (fl.) 500 mm, ocular (o.) 10 mm) and second telescope (fl. 1000 mm, o. 20 mm)? (both 50 x)

The larger the entrance aperture, the greater the light-collecting capability. Now, you didn't specify that, but that does matter in your final choice. Next, as the comments suggest, the choice of ...
Carl Witthoft's user avatar
3 votes

What's the cheapest lens to buy for showing ISS to a flat earther?

No such thing as a Nikon P9000 .... there are the P900 and P1000 model cameras, which come with a non-detachable lens, which can be zoomed to extreme focal lengths, included. These have indeed a good ...
rackandboneman's user avatar
3 votes

How do focal length, angular magnification and field of view relate?

Magnification and Field of View are directly opposite. A low magnification will give a large field of view, and a high magnification will give a small field of view. (Field of view indicates how "wide"...
JohnHoltz's user avatar
  • 8,032
3 votes
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How do focal length, angular magnification and field of view relate?

For the relation between magnification and field of view, imaging enlarging pictures, but you can only print out pictures on one size of paper. If you don't have a lot of magnification, you can draw ...
usernumber's user avatar
  • 17.5k

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