10

I'm not sure it counts as "simple" but there is the ice cube neutrino observatory whose detector consists of a cubic kilometer of very clear ice a mile or so down in the antarctic icecap.


9

The first question anyone asks about a telescope is "what is the magnification?" It is almost always not the most important thing. Any telescope can magnify a million times, given a short enough eyepiece - the problem is, how good the image is. For observing planets, the main thing is resolving power - the ability of the telescope to discern tiny details. ...


6

The material used for the mirror is indeed E6 Borosilicate manufactured by Ohara corporation as pointed out by @notovny. The fabrication process of a borosilicate glass honeycomb mirror has remained almost unchanged since the first one, an 8.4m LBT mirror, was cast in 1997 (here is the article of the casting). Quoting the article: E6 is a good match to our ...


6

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 polishing strokes, and feedback via control and testing. https://stellafane.org/tm/atm/mirror-refs/strokes.html Normal polishing strokes (center over center, ...


4

Here's what I've learned from making telescope mirrors. Start with a mirror that's of a reasonable size and curvature. It is definitely possible to begin with a 12" f/5 mirror, but the problem is you have to handle not just the higher volume of work, but also the learning process in a field that's completely new to you. Begin with making a 6" f/8 mirror. ...


4

I second the comment about Texereau -- originally written in French; it's the best, bar none. You won't need anything else. Remember the old adage that is quicker to make a 4" mirror and then an 8" mirror than it is to make an 8" mirror first. Don't bother with borosilicate. You should be able to get mirror kits and all the abrasives that you need online. ...


4

In the first chapter of Out of the Darkness: The Planet Pluto, Tombaugh gives a colorful, personal account of his youth in Illinois and Kansas, including five telescopes: his uncle's uncorrected 3-inch refractor a 2.25-inch achromatic Sears-Roebuck refractor his father and uncle shared a mediocre 8-inch reflector he made in 1926 a better 7-inch reflector he ...


4

Front-surface glass mirrors weren't developed until the 1850s. Before that, the most common material was speculum metal, a high-tin bronze. Notable examples include Isaac Newton's 1668 prototype and William Herschel's late 18th century telescopes. Since speculum metal tarnished easily, it was common to have a spare mirror to continue observations while the ...


3

There basically are three main properties which influence what you see with your telescope: The aperture defines how much light you get, thus how sensitive your setup will get. The bigger, the more light you collect, thus the fainter objects you will be able to detect in principle. There's the somewhat sense-free saying that you can compensate (clear) ...


3

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 to see craters, mountains and valleys on the Moon. You will probably not see planetary disks or the rings of Saturn. The large diameter of the ocular might be ...


3

You would be better off using lens 5 and 3. Though don't expect much, a simple single lens for the objective and for the eyepiece will give a lot of chromatic aberration (false colour). Refracting telescopes usually use at least two lens of different glass types (crown & flint often in a doublet) and eyepieces usually have 4+ lens. You should be able to ...


3

1 A.U. is same as infinity. The difference in terms of eyepiece position is infinitesimal, you can't measure it. Anything beyond a few kilometers away is pretty much "at infinity". Regardless of that - from the practice of designing and building telescopes, calculations only offer you a starting point. You do the math, and the distance is 105 cm. But in ...


2

I generally agree with the answer above, but have a couple more insights which might help you if you decide to proceed with trying to make your own scope... The lens pairs that James mentioned (crown and flint) are known as a doublet. Glass has two key properties in play here - its index of refraction (how much it bends light) and its dispersion (how much ...


2

This is a coincidence, but it seems that the photographer Mathieu Stern has been thinking about making and using an ice lens for photography for years. The video linked below was just recently released. See their blogpost and their YouTube video I made a CAMERA LENS with an ICEBERG. I'm going to call this an "almost" telescope in that a large ...


2

Has anyone ever tried to make a simple telescope using ice? I have done some research and not found any evidence of an attempt to build one. Another poster has added information on a neutrino telescope that relies on ice. If that's the kind of telescope you're looking for, then there's an example. Is it theoretically possible to build an optical one? Yes, ...


2

If you use the 100cm FL convex lens as an objective and the 20cm FL concave lens as an eyepiece, the telescope will have only 5x magnification but otherwise be similar to the one Galileo used to discover the four largest moons of Jupiter. Here is documentation of such a telescope built by students. Beyond 10x or so, you need a steady mount for the telescope, ...


2

I don't have enough room in the comments for this, so I'm writing here, although it's probably not a true answer since I know nothing about that particular telescope. Anyway, if you look at many SCT systems, and their derivatives such as Ritchey-Chretien, Dall-Kirkham, etc, the distance between primary and secondary is often not too big. If the secondary ...


2

Is this because I have not used achromatic lens? An easy way to check for the effects of chromatic aberration will be to look at a narrow wavelength source. These days that's easy because the spread in wavelengths from single color LEDs is only 10 to 20 nm1 depending on the specific LED. If you can find something with red, green or yellow LEDs (not the ...


2

Can a material other than glass be used for making telescope mirrors? Yes! From this answer to Why are telescope mirrors made of glass? They are not always made of glass. In situations where mass counts and thermal variations can be large, optical telescope mirrors are sometimes made out of silicon carbide instead. From this answer to How are space ...


1

Astronomical objects are so far away that they focus the same point as an object at infinite distance. In fact any object more than a hundred metres away or so can be treated as being an infinite distance. To quantify this consider the focal distance equation: $\frac{1}{f}=\frac{1}{d_o}+\frac{1}{d_i}$ If the focal distance = 1m, and the object distance $...


1

There are a few rules of thumb you will need: Maximum useful magnification $M_{max}\approx D\times 50$ where $D$ is the diameter of the objective is in inches, and magnification $M=l_{obj}/l_{eye}$, where $l_{obj}$ and $l_{eye}$ are the focal lengths of the objective and eye piece respectively.


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