Questions tagged [telescope-lens]

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3 votes
3 answers
327 views

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

I have a Celestron Specialty Series Travel Scope 70mm refractor which came with 10mm (40x) and 20mm (20x) eyepieces. Specifications: Focal ratio: f/5.71 Optical Design: Refractor Aperture (mm): 70 mm ...
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7 votes
1 answer
549 views

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

I am trying to understand what is meant by par. lines in an 1867 article "The Aberration of the fixed stars after the wave theory" by Prof. W. Klinkerfues of Royal Astronomy Works of ...
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1 vote
1 answer
50 views

Can I use an achromatic focal reducer to reduce chromatic aberration?

I am using 75/1000 Plano convex lens to build telescope. Can I use an achromatic focal reducer to reduce chromatic aberration?
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2 votes
1 answer
153 views

Not Able to View Objects with Barlow Lens

I am new to using a telescope and am having a hard time using a Barlow lens. I was able to find Jupiter multiple times using a 6mm lens with a telescope that has a D = 60mm and FL = 700mm. I am very ...
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  • 21
1 vote
1 answer
101 views

Choosing an eyepiece for planet viewing

I have a Celestron Astromaster 130EQ which came with a 10mm and 20mm lens. I can not see mars, Jupiter, or Saturn as expected, I only see white dots. What lens should I buy to view these planets.
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3 votes
0 answers
57 views

Could we see small objects like animals on an exoplanet using Solar Gravitational Lensing (SGL) if we could use any star or a black hole for lensing?

Theoretically, if a telescope is positioned in a focal point of a supermassive black hole or a star much more massive than the Sun, would there be a limit to how far away an observable planet can be ...
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2 votes
2 answers
91 views

Cellphone astronomy cams

How long until cellphone cams became so good that we could watch planets with their focal power like a telescope lens? Neglecting SpaceX and Bezos satellites (at least from the moment), how far are we ...
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3 votes
0 answers
38 views

Can you advise on the construction of a large segmented primary mirror (hobbiest)?

I am interested in experimenting with the building of a large parabolic primary mirror constructed from 4" hexagon mirrors mounted on a "rough" parabolic surface with either 3 screw ...
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3 votes
1 answer
69 views

Diameter of the moon from the diameter seen in the telescope

I'm reading a chapter on convex lenses and it has this diagram: The chapter explains that triangles ABC and ADE are similar. Thus, ratio of CB to DE is equal to the ratio of BA to AD. Does this mean ...
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2 votes
1 answer
136 views

Fresnel lenses for a makeshift Galilei telescope?

For a kindergarden (pirate) party, friends of me want to build together with the 4 year old kids a functional pirate's telescope for each of the kids. On the web I found full constuction sets, e.g. ...
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  • 5,284
2 votes
1 answer
79 views

Telescope lens problem when cold

We are having a problem with our scopes on cold nights. (-10F is about average here.) One poorly aimed breath means that the eyepiece lens fogs. We have to remove the lens and keep it under our arms ...
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  • 1,519
1 vote
1 answer
316 views

How to estimate my eyepiece FOV?

As a follow-on to my question about seeing Jupiter and Saturn at the same time in my scope, I'd like to ask how I might determine the Field of View (FOV) of my eyepieces. More specifically, I'd like ...
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  • 363
1 vote
1 answer
450 views

Eyepieces and accessories recommendations for a Starblast 4.5-inch scope in a city as well as darker suburbs, and kid friendly?

For the Starblast 4.5 Telescope I currently have an Orion 7-21mm Zoom eyepiece attached on top of a 2x Barlow lens. I like them because of the magnification they give stacked together and the zoom ...
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1 vote
1 answer
60 views

TASCO 49060700 60x700mm Spacestation Refractor

So, my grandfather so graciously gave me his TASCO 49060700 60x700mm Spacestation Refractor Telescope, which is extremely wondrous. Any way, I found this answer to my 3x barlow lens, which I believe ...
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1 vote
2 answers
129 views

What are the effects of using non-spherical lenses in refracting telescopes?

Non-spherical (or non-circular) mirrors for reflecting telescopes are common and discussed in many places... But what about elliptical, parabolic or hyperbolic lenses?
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  • 3,333
1 vote
1 answer
105 views

Problem with making telescope

I am using a convex lens with $f=5$ cm and $5$ cm aperture, a concavo-convex lens with $f=100$ cm and $5.5$ cm aperture. I am trying to make telescope and it should have magnification of 20 x. But the ...
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3 votes
1 answer
305 views

How can I improve the Field of View of my home-made telescope?

I made my telescope, with two convex lens of focal length 1000mm and eyepiece (plano-convex) with 25mm focal length. But I can see only a very small field of view, with inverted image. Do I need to ...
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  • 41
4 votes
4 answers
515 views

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

The larger the focal length the larger the angular magnification The smaller the focal length the larger the field of view. I don't understand why this applies. I'm talking specifically about ...
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  • 201
1 vote
1 answer
185 views

Verifying refractor lens about scratches

I found an used Skywatcher 70mm telescope for buying, but its lenses are a little suspect about harming. In one photo, it looks clearly a scratch, but in the another, it is not visible. Could it be an ...
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  • 143
2 votes
3 answers
217 views

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

Recently I entered a discussion with someone that has a relatively popular YouTube channel which says among other things that the earth is flat. I said that earth isn't flat because you can see the ...
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  • 123
2 votes
1 answer
195 views

Difference between first (focal length (fl.) 500 mm, ocular (o.) 10 mm) and second telescope (fl. 1000 mm, o. 20 mm)? (both 50 x)

Magnification is defined as $f_{objectiv}/f_{ocular}$. If I had the first telescope with the focal length of 500 mm, ocular 10 mm and second telescope with the focal length of 1000 mm, ocular 20 mm, ...
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  • 2,660
2 votes
1 answer
198 views

Telescope focal point and inversion

When looking at a diagram of the optical path through a newtonian reflector, the lines always cross before the eyepiece. I understand that the eyepiece is used to focus this diverging light cone so ...
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  • 21
2 votes
3 answers
386 views

How did Johannes Hevelius' long telescope work? Why all the round holes?

The drawing below, found in Wikimedia and at lib.harvard.edu is of a very long tubed aerial telescope. I believe it is taken from his 1673 work Machinae coelestis. I've always wondered about the ...
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  • 31.6k
3 votes
0 answers
80 views

Combining lenses from two telescopes to build a more powerful one?

I have two Galileo 700mm x 60mm Astro/Terrestrial Refractor Telescopes. Can I take the lenses out and make one powerful telescope, something like an optical series circuit?
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2 votes
2 answers
996 views

What soviet telescope is this?

A friend has a vintage telescope with a broken lens, I asked him to send me its catalog so I can see if I can buy him a new one, he gave me what looks like a Russian catalog, it seems a soviet ...
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  • 151
2 votes
1 answer
123 views

What are some formulas that are associated with the Schmidt corrector?

I want to fully understand how an SCT works. Thus, I figured out I can use some formulas that describe how an incident ray that is parallel with the axis would act after refracting off a Schmidt plate....
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2 votes
2 answers
1k views

What are the aberrations of an SCT? And how can they be eliminated?

The Schmidt-Cassegrain telescope is amazing! It is compact, suitable for astrophotography ,and it requires little to no collimation. However, the SCT has some inherent optical issues. What are they? ...
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1 vote
1 answer
200 views

Why aren't corrector plates aligned with the center of curvature in an SCT?

According to wikipedia, Schmidt corrector plates must be aligned with the center of curvature to eliminate the spherical aberration. However, in compact SCT designs by Celestron and Meade, that is ...
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3 votes
2 answers
131 views

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

Could a lens or mirror be placed in orbit on the same flight path with other parts to make a telescope or on the horizon of the moon to see farther with the Hubble?
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  • 1
0 votes
1 answer
155 views

what kind of telescope eyepieces is best for viewing planets up close

ok so I am a total amateur when it comes to telescopes and lens, and this is probably a pretty stupid question, but I am trying to find a lens/eyepiece that is good for viewing Jupiter and Saturn up ...
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4 votes
3 answers
2k views

Relation between angular resolution and aperture?

The angular resolution of a telescope is given by $\frac{1.22\lambda}{D}$. This should mean that the smaller the aperture D, the higher the angular resolution. But it is exactly the opposite - why?
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3 votes
2 answers
208 views

Need help in creating telescope

I have 100cm F.L objective and 10cm F.L eyepiece 10cm in diameter and double convex both. what are the planetary objects I can see with telescope made with these lenses. I also have a double convex ...
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  • 133
1 vote
1 answer
863 views

How can I find out the maximum magnification of my telescope?

I have a Meade DS-2080AT-LNT. It's an inexpensive scope that I've had for several years. It has a couple of eyepieces with it, but nothing that will let you get a really good look at planets. I doubt ...
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  • 113
8 votes
1 answer
1k views

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

I understand polishing the mirror with a successively finer abrasive can create a curvature, but how is it possible to obtain a uniform curve that forms a parabola while polishing by hand?
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0 votes
1 answer
175 views

Possible to make a cheap reflective objective lens with a mirror?

Sounds kinda crazy and cheap but has anyone ever tried to take a flexible (plastic) mirror and attach a string to the back side then pull the string so it makes a concave surface? I realize it wouldn'...
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2 votes
1 answer
2k views

In a reflecting telescope (Cassegrain), is there a difference between using a concave or convex secondary mirror?

These are two diagrams of Cassegrain reflecting telescopes. One uses a concave secondary mirror, and the other uses a convex one. Is there any difference between the two? For example, does one cost ...
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1 vote
1 answer
74 views

What is the next lens I should buy? [closed]

I have a question about purchasing another lens that's right for my situation. I own the Orion Skyquest XT10 Dobsonian, a classic case of buying a scope that is WAY to big to be carrying around ...
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4 votes
1 answer
2k views

Constructing a periscope/telescope - trouble with lenses

Not sure if this is the best place for this, maybe physics would be a better fit, but I'm trying to build a periscope and am running into an issue. Traditional mirror periscopes work well, but when ...
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-2 votes
1 answer
268 views

Does making a ground based telescope larger always give you a better resolution?? why?? or why not? [closed]

i just don't really understand this topic.
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2 votes
1 answer
189 views

What type of telescope can show cliffs on the moon surface from a city location?

I am a complete novice in this world and I would like a telescope where I could have enough power to view the moon's surface, I don't expect to see the flag or the hover sending signs to me, but ...
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  • 121
5 votes
6 answers
4k views

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

If we were to make telescopes with Fresnel lenses instead of regular lenses, would it be more practical? Would this also allow for much bigger telescopes to be made? Here is an example of the type ...
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  • 3,919
0 votes
2 answers
336 views

Tunnel vision while viewing through a reflector

I have a Celestron astromaster130 eq. While viewing through its eyepiece, or using a smartphone camera for photography purpose there is always a definitive no light region( it is circular in curvature)...
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  • 285
9 votes
1 answer
8k views

How much of a difference do good lenses make?

I recently purchased a Celestron PowerSeeker 114EQ and with it I got three lenses (which I assume are low quality), a 4mm, a 20mm and a 3 x Barlow. I can get pretty decent views of the moon but a ...
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  • 193
12 votes
3 answers
876 views

What was the largest telescope ever fitted with an eyepiece

Serious modern telescopes use CCDs to capture the results. This makes it convenient to process or display the results halfway around the world. However, there is something visceral about looking ...
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4 votes
1 answer
1k views

Focusing light through fiber optic cable to extend telescope viewer

I want to build a system to view my telescope without being uncomfortable. Currently I have to stand up and bend over to view the eye piece. I want to build a system that allows me to 'pipe' the ...
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  • 141
1 vote
1 answer
723 views

How to view Jupiter with 4.5" Newtonian Reflector

I have a 4.5" Newtonian Reflector and I took a look at Jupiter the other night. I was able to get a reasonably sharp view of it and see a number of it's moons, but I was unable to see any surface ...
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  • 140
8 votes
1 answer
911 views

Which type of telescope should I make?

I am not very much interested in observational physics but I just like to look at the night sky. It gives me a lot of inspiration. So, i was thinking about making a telescope for basic observations. I ...
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  • 720
8 votes
1 answer
266 views

What is a Barlow lens?

I am looking to buy a Celestron 21023 FirstScope 76 Telescope, which is quite inexpensive, and it has good reviews on Amazon. One thing that many reviewers have said is that the two lenses that it ...
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11 votes
1 answer
224 views

Dealing with damp and dew whilst stargazing at night or in the early morning

Sometimes when using my telescope late at night or early in the morning, especially in the more humid of seasons, I notice i sometimes get dew buildup on the lenses. How can I minimize damp buildup ...
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11 votes
1 answer
522 views

How can I clean my lenses without causing scratching or damages to the lens surface?

Sometimes you can be trying to observe very faint or very small objects in the sky and it wouldn't pay to have these obscured or marred by a scratch or dust on the lenses. I keep to good practices ...
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