11

It's probably impossible to prevent chromatic aberration, since there is no such thing as a perfectly achromatic lens. but you can certainly minimize it. As you have mentioned, for a given spectral range, the best way is to choose a lens that is said to be "achromatic" even though the correction is never perfect. But if you want to use a lens that is not ...


11

All telescopes have in common that they gather and focus light from far away objects. They use a primary opical element, such as a concave mirror or a (planar- or bi-)convex lense (or lense system), and they use an eyepiece with another lense system (for viewing) or a camera in their primary focus. A refractor telescope does not sharpen the image per se. ...


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. ...


7

Yes, stacking Barlow lenses is a common practice to effectively increase focal length by multiplying their individual focal lengths. When I say common, most advanced eyepieces actually have many glass elements and are a type of a Barlow lens themselves, so just by using a single Barlow lens in front of your eyepiece you'd already be, technically, stacking ...


5

The Moon is the easiest target to start with. After that, try whichever bright planets are currently in the sky: Jupiter, Saturn, Mars, Venus. Then get a star map and try to find some of the brighter star clusters, nebulas, and galaxies. I recommend the monthly sky maps and object lists at Skymaps.com. Latitude 19°N falls midway between their northern ...


5

Canon camera has another method to reduce or cancel chromatic abberation they call Diffractive Optics. The idea is to use a lens with a diffraction pattern in it that causes the chromatic aberration to bend the opposite way from normal lenses. So if blue is bending the most through the normal lens, then it will bend the least when going through the ...


5

A fouth approach to add to @Uhoh's 3 others, is to make the lens of extra low dispersion glass. Dispersion is a measure of how refractive index varies with colour. However such glass is relatively difficult to make, in the quality required for lenses, and so rather expensive. Further information about dispersion can be found on this wikipedia page https:/...


4

An 18.5 inch telescope is easily large enough to collect the photons you require. So long as you have a good CCD camera, with a pixel size on the sky that is considerably smaller than the "seeing" and you take a great deal of care in how you make and analyse the observations. Exposure times can be minutes if necessary, because a typical transit lasts a ...


4

A bright, nearby star with a large exoplanet would be best. For example, the first star to have a transiting planet observed was HD 209458, in Pegasus. It has a magnitude of 7.65. When the large "hot jupiter" transits the star it dims by a relative flux of 0.984. That corresponds to a change in magnitude of about 0.016. I.e. it changes from a magnitude 7.65 ...


3

This is a really interesting question! The Dragonfly telescope described below takes advantage of the fact that on Earth, the optical surfaces of some lenses can generate less diffuse scattering than the optical surfaces of reflecting telescopes. If you were worrying about scattering from secondary mirrors you could make an off-axis primary, but at a ...


3

Further would a Barlow lens solve the chromatic aberration issues with a f/5 refractor. I suppose in theory they could, but they would have to be designed to do so. In practice, they vary widely in quality, and either don't have an effect on chromatic aberration, or actually make it worse. Which would be a better option? There is no objective way of ...


3

1. Resolving power and diffraction Diffraction happens anywhere there's an edge. "It is defined as the bending of light around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle." (Wikipedia) So all you need for diffraction is an obstacle of any shape - at the edge of the obstacle, the light will bend a little. In ...


3

I'll attempt to answer as many of these questions, to the best of my abilities, as I can at this late hour. 1) Lenses have an index of refraction that is different than vacuum, and air, and they are curved. ie: corners when light is concerned. 2) The entrance and exit pupils are the pupil size required to pass an "extreme" ray through an optic. Meaning ...


3

Actually, your Newtonian may run the risk of suffering from the projection method. The secondary, planar mirror in the Newtonian will be subject to heating. Although it is not in the prime focal point, the light rays are already pretty much bundled up, and this may lead to heating and ultimately to failure of the secondary mirror! With refractors, you don't ...


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 ...


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

It depend where vibration are. Often (if you have a good mount for the telescope) all the structure vibrate and there are some good anti-vibration feet that can be useful. If the tripod isn't the problem and the vibration are only near the telescope, probably the problem is the mount that is under-sized for you telescope. In this case the only good way is ...


2

The refractor will be better for wide-field observing of starfields and big nebula and galaxies. For planets and small to medium (also larger with 2" eyepieces or just 1.25" eyepieces with a low magnification and big apparent field of view) sized DSOs (nebulae, galaxies and star clusters) the reflector will have an advantage due to its aperture. The only ...


2

Item B is called a visual back. The new focuser would just replace this, and screw onto item A. The focuser you link to is designed for a refractor, but you need one for a SCT, like this https://www.firstlightoptics.com/skywatcher-focusers/dual-speed-2-crayford-focuser-for-sct-telescopes.html There are lots of different makes and prices. Regarding the ...


1

It's 70mm aperture, so the maximum useful magnification will be 165x. If you have a 4mm eyepiece, you will have 75x magnification, and at that, you can expect to see rings of Saturn, moons of Jupiter in good conditions. Venus will show phases. I can't say much about Mercury. You can see many surface features of the Moon. The view will be particularly good at ...


1

There is a wide variety of telescopes, so it's a bit difficult to give a general answer, but here are some pointers: If there is an open-end, it likely is a reflector telescope (perhaps a Newton). In this case, you can see the secondary mirror attached inside. When you look through the place where you set the eyepiece, are you facing the same direction as ...


1

I have viewed through many telescopes over the years and in doing so have met many people like yourself. To suggest a F/12.5 Maksutov will satisfy you would be the equivalent of telling someone to dive into the deep end of a swimming pool without knowing if that person can swim. If it's bang for buck that motivated your question I think you would get the ...


1

First off I want to say I am a complete amateur when it comes to stars and even bigger when it comes to optics. I was looking at sky from indoors and my windows have double glass. It turns out that this was the problem or maybe the glass on the window is not some good quality. In any case, all works well now and I am thrilled at what I'm seeing in the ...


1

Meade make the 497 auto star hand controller, which plugs in where your existing hand controller goes. This turns your mount into a fully computerised one. Alternatively you should be able to use a laptop to control the mount via the aux ports. It’s all in the manual. If your telescope did not originally come with the auto star hand controller, here is a ...


1

Depending on the root cause, vibration damping pads may or may not help. Some telescope vendors sell sets of three for $50 or so; an Internet search also yields a few do-it-yourself recipes using silicone caulk, sorbothane insoles, etc. Other home remedies are possible, such as adding weight or shims to the mount, or hanging a chain from the optical tube ...


1

You already have an answer but there are a few interesting Physics things in your question that are linked: 1) Diffraction and the fact that telescopes have no "slit". 5) Stars don't appear as a sphere, they appear as dots. The telescope has a round aperture (of say 60mm or so) and this behaves as a slit in some ways. It causes diffraction patterns (an ...


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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