Questions tagged [telescope-lens]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
1
vote
1answer
44 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 ...
2
votes
3answers
174 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 ...
0
votes
1answer
72 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, ...
2
votes
1answer
32 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 ...
2
votes
3answers
205 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 ...
2
votes
2answers
376 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 ...
2
votes
1answer
51 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....
2
votes
2answers
285 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? ...
1
vote
1answer
104 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 ...
3
votes
2answers
113 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?
0
votes
1answer
103 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 ...
4
votes
3answers
910 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?
3
votes
2answers
161 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 ...
1
vote
1answer
400 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 ...
8
votes
1answer
485 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?
0
votes
1answer
130 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'...
1
vote
1answer
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 ...
1
vote
1answer
71 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 ...
4
votes
1answer
1k 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 ...
2
votes
1answer
141 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 ...
5
votes
6answers
2k 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 ...
0
votes
2answers
275 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)...
9
votes
1answer
3k 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 ...
8
votes
3answers
498 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 ...
4
votes
1answer
930 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 ...
1
vote
1answer
445 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 ...
6
votes
1answer
818 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 ...
9
votes
1answer
195 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 ...
10
votes
1answer
180 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 ...
10
votes
1answer
453 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 ...
10
votes
2answers
5k views

Are Barlow Lenses Good For Deep Sky Observing?

I'm using a 750mm (focal length) by 150mm (aperture) newtonian reflector and I've been curious about using Barlow lenses on deep sky objects. Some of the astronomers at my local observatory say that ...