However, if you were to view the same image through one that has got better resolving power, you would be able to see the details clearer. How is the resolving power measured? This is measured by the absolute smallest angle that can be resolved.

Did you know that there are some really powerful modern telescopes that are capable of counting the number of lines in President Roosevelt’s hair that was placed upon a dime located 3.7 kilometers away? For astronomers, it is all about getting the best telescopes with the greatest resolving power as this means that they would be able to view celestial objects better. This is also one of the reasons as to why radio telescopes are far bigger than their optical counterparts.

A good way of increasing resolution is to make an interferometer which is basically connecting telescopes together. The image would have the same sharpness as one that was taken by a single instrument which would extend from one end of this interferometer to another.

So there you have it, a few bits and bobs with regards to gauging a telescope’s resolving power.

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Not only does astronomy cover different branches of science, it also borrows concepts in fiber optics as well. Objective (optics) is also taken into account when it comes to science, or in this case, astronomy.

Objective (optics) means the optical part of a scientific instrument such as a telescope or microscope, that is responsible for gathering light from the observed specimen and makes sure that these light rays are then focused at different levels to produce the real image.

In space studies, Objective (optics) is the optical part of the telescope. It is the lens located at the end of the refractor or simply put, is the front end of the telescope, where people usually set and focus at a fixed point in the sky or at a long distance. This is not to be confused with the other end of the telescope, where people usually take a look on the area being fixed upon. The light gathering capability and the maximum distance it can take is dictated by the diameter or size of the lens. This means that the bigger the objective lens a certain telescope has, it means that the dimmer the object it is focused on and more details can be shown or seen.

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The eye relief is an important concept in the use of equipments like a telescope, microscope, or binoculars. By definition, eye relief is the distance from the eye piece at which the eye can be placed to the entrance pupil of the eye. Instruments with short eye relief will require the observer to press their eyes closer to the eye piece to see a clear image. Eye relief illustrated by # 3 in image.

Exit pupil larger than the pupil will waste the light, but allows more movement without a vignette. On the other hand, an exit relief smaller than the pupil causes a vignette image. Without the proper eye relief, you cannot enjoy your binoculars or eye piece properly.

Eye relief is very important for those who eyeglasses, too. Having a longer eye relief means a broader field of view. It is recommended for eyeglass wearers to have at least an eye relief rating from 14 mm to 23 mm.

Eye relief also plays an important role to shooters, as a vital safety consideration. Too short relief and the skin between the optic and the eyebrow will get cut because of recoil. This is called ?idiot cut?. Having an exit pupil larger than your pupil will allow you a clear view without vignetting.

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In physics, focus is defined as that point in which the rays of light converge or meet; or diverge in the case when light is refracted or reflected. In optics, it can mean a number of things including:

? A lens? focal point
? A lens? or a telescope?s eyepiece?s focal length
? The condition by which an object being viewed through an optical system is seen; either being in or out of focus
? A device used in optical systems in order to adjust its focal length, thereby making an image clearer

An image is in focus when the light from the object converges on almost one single point in the image, while an object out of focus will have light from it not converging very well.

In astronomy, interest in foci is usually concentrated to telescope use. To get a good view of distant objects in the sky, a telescope must be properly focused. Focusing of telescopes is easy, and comes instinctively even to beginners.

Adjusting the focus of a telescope is usually done either by moving its eyepiece or its primary mirror. This can be done by turning the wheels of a geared system, called the rack and pinion; or by turning a screw knob on the back of a telescope.

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Photo by: Tamasflex Creative Commons

If you recently have had a conversation with an astronomer, then you’ve probably heard them mention the exit pupil as a certain eye piece in telescopes or binoculars. But what does exit pupil really mean, and how can it affect views when looking through a telescope?

By definition, exit pupil is the image of an object projected by the eye piece. Thus, all light passes through the exit pupil, and it should ideally be the same size as the pupil of your eye. Any millimeter larger can be harmful.

The exit pupil is calculated as the objective diameter partitioned by magnification. To find your binoculars’ or telescope’s exit pupil, determine the focal length of the instrument and divide it with the focal length of your eye piece. This will give the magnification of the telescope. Then divide the objective diameter by the magnification. Make sure to do this in the same unit, in millimeter.

An exact exit pupil for your telescope or binoculars means that it will provide a more detailed view of objects. You can even see the faintest objects in the farthest horizon. Exit pupils larger than 5 mm will tend to wash out detail and objects will be faint.

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Separated from a telescope, a typical eyepiece would have a FOV of 40? to 65? and above; this is regarded as the apparent field of view. A smaller, true or actual field of view results when the eyepiece is inserted into the telescope. To calculate the actual field of view of a telescope, divide the apparent field

of view with the telescope?s magnification. For example, a telescope with a magnification of x40 will have a 1? FOV if the eyepiece used in it has an apparent FOV of 40?.

If you don?t know your telescope?s magnification or the FOV of its eyepiece, you can easily calculate the field of view of any telescope combined with any eyepiece using the drift method. In this method, you point the telescope at a star near the celestial equator and time how long that star moves across the telescope?s field of view (from edge to edge). This can be calculated using the following formula:

FOV = (Drift time) x cosine (star?s declination) x 360? / 86,164 seconds

Or with a much simpler formula:

FOV = drift time/240 seconds

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In optical systems with multiple mirrors or lenses, the focal length is usually called the EFL or the effective focal length; distinguishing it from the FFL (front focal length) and the BFL (back focal length).

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There are basically two lenses in an eyepiece: one is the field lens, which is where light passes through and images of the object are collected; and the eye lens where the observer looks through and sees the image. The viewer then can magnify or sharpen whatever he is seeing with the use of the aperture. The number of magnification depends on the focal length, the distance of the field lens to the eye lens, of an object.

There are also different kinds of eyepieces, ranging from the simpler to complex ones. Some have low field of view, while others are so powerful they are best for lunar or planetary observations. Huygenian eyepiece uses two convex lenses, which is simple. The Kellner eyepiece has two convex lenses but their flat surface facing outwards, plus an achromat for the eye lens. Another one is the orthoscopic eyepiece, which consists of three-cemented field lens with a single convex eye lens. There are also other types of eyepiece.

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