what is focal length telescope

What is the best lens for a telescope?

Best Telescope Lenses. 1. Celestron 93230 8 to 24mm 1.25 Zoom Eyepiece. 2. Orion 8200 3.6mm E-series Telescope Eyepiece. 3. Baader Planetarium 8-24mm Hyperion Clickstop Zoom Mark IV Eyepiece. 4. Explore Scientific 82 Degree Series Gas Purged 11mm Waterproof Telescope Eyepiece.

What is the length of a telescope in normal adjustment?

the main function of adjustment for a refractor telescope is not to make up for individual eyepiece’s focal length, although a lot of telescopes may require adjustment when doing so , but this adjustment is minor compared with the adjustment required when one minute you are observing something 50 metres distant then adjust to look at the heavens , this requires far more adjustment , for example a telescope with focal length of 75″ requires around 5″ of adjustment to change from these ...

What does focal ratio mean in telescopes?

Focal ratio is the ratio between the diameter of a telescopes objective lens or mirror, and the distance to the focal point. For example if the objective is 100 mms in diameter and the focal point is 1000 mm, the focal ratio is f/10. Generally speaking, the longer the f/ratio, the higher the magnification for a given eyepiece.

How is focal length used in astronomy?

Focal length is the distance the light travels to go from the entry to the exit point in a telescope. The focal length is important to determine the magnification and field of view of the resulting image. A long focal length is good for observing planets, a short focal length is good for observing deep space objects.

What is the meaning of focal length for telescope?

Generally expressed, focal length is the distance (given in millimeters) between the telescope's primary lens or mirror and the point where the light rays come together in focus.

Is higher focal length better for telescope?

A longer focal length will shorten the field of view but increase magnification, which is ideal for observing planets and the moon. A shorter focal length offers a larger field of view which is better for astrophotography and observing galaxies, nebulas, and other deep sky objects as they are larger but dimmer targets.

Is 400mm focal length good for telescope?

* 400mm (f/5.7) focal length and 70mm aperture, fully coated optical glass lens, with high transmission coating, can create stunning images and protect your eyes. The perfect telescope for astronomers to explore the stars and moon.

What can I see with a 700mm focal length telescope?

With a 70mm telescope, you will easily be able to see every planet in the Solar System. You will also be able to take a great look at the Moon and clearly distinguish most of its recognizable features and craters.

What kind of telescope is best for viewing planets?

If you're wanting to view faint deep-sky objects like nebulas and galaxies then you'll want a reflector telescope whereas a refractor telescope is better suited for views within our own galaxy such as the moon and other planets.

Is a 900mm telescope good?

The focal length of the telescope is 900mm, so to achieve the maximum useful magnification, then a 4.5mm eyepiece would be ideal. One of the best parts about planetary viewing or imaging is that since the objects are so bright, you can do it just about anywhere regardless of light pollution.

What can I see with a 400mm focal length telescope?

With 400mm you could watch objects like:Andromeda galaxy core.Orion nebula, other large emission or reflective nebulae (e.g. Pleiades)large star clusters.low magnification lunar observations.

How do I choose a telescope for a beginner?

Bigger is better, or is it? The main specification you want to consider when choosing a telescope is its aperture—the diameter of its main mirror or lens. The larger the diameter, the more light the telescope collects, allowing you to see fainter objects and more detail on nearby, bright objects like the Moon.

What can you see with a 200mm telescope?

200 mm refractors, 250 mm reflectors and catadioptric telescopes (and beyond): binary stars with angular separation of 0.5" (under ideal conditions), faint stars (up to 15 stellar magnitude); lunar features (less than 1.5 km in diameter);

Can you see Saturn's rings with a 70mm telescope?

The colorful bands and belts of Jupiter, as well as its four major moons, and the rings of Saturn are clearly visible in a 70mm telescope.

How big of a telescope do you need to see Saturn rings?

The rings of Saturn should be visible in even the smallest telescope at 25x. A good 3-inch scope at 50x can show them as a separate structure detached on all sides from the ball of the planet.

Can you see the moon with a 50mm telescope?

Telescope measurements and specifications are generally given in metric system units (millimeters, centimeters, etc). With a 50mm telescope, the Moon will look great and you will be able to see al the major craters and geological features.

What focal length is best for telescope?

The main specifications for a really useful first telescope should be: a minimum aperture of at least 90mm for a refractor or 130mm for a reflector and 1,000mm focal length for each. This combination will provide enough light grasp and permit a high enough magnification to see detail on the brighter planets.

What is a good focal ratio for a telescope?

Focal Ratio – Faster, Brighter, Smaller A long focal ratio implies higher magnification and narrower field of view with a given eyepiece, which is great for observing the moon and planets and double stars. For such objects, a focal ratio of f/10 or more is ideal.

Is longer focal length better?

The longer the focal length, the narrower the angle of view and the higher the magnification. The shorter the focal length, the wider the angle of view and the lower the magnification.

What size lens is best for telescope?

The most common and time-tested rule of thumb suggests not exceeding a magnification of about 50x per inch of aperture of your scope. For a 4" telescope, for example, you should stick to less than 200x with your shortest focal length eyepiece. Any higher and the view will become unacceptably dim and less sharp.

What does focal length do in a telescope?

Ok, now we know what focal length is. But what does it do and why does it matter?

How to increase or decrease the focal length of a telescope

Even though the focal length of a telescope is unchangeable, there are ways to artificially extend it by using certain accessories like a Barlow lens or a focal extender.

Focal length vs aperture

There is some debate on which number is the most important specification for a telescope. Aperture or focal length?

Conclusions

Focal length is the distance the light travels to go from the entry to the exit point in a telescope.

What is focal length?

Contrary to popular belief, the focal length is the distance, measured in millimeters, from the center of the aperture to the point where the image is formed. This point in the telescope is where the eyepiece connects and takes in the light from the aperture. Unlike other lenses, the focal length of a telescope is usually ...

How to tell focal length in inches?

An inch is roughly 25mm. That means that you can divide all of your focal lengths by 25 to get a rough approximation in inches. This can help when visualizing how long the focal length actually is for anyone who is not fluent in the metric system.

Why do reflectors have a short focal ratio?

That is why reflectors usually have a very short focal ratio compared to refractor telescopes. Reflectors thrive on wide angle shots while refractors perform better with narrow angle shots. This will affect the image quality depending on what kind of image you are trying to process with your telescope.

Why is there extra space in the optical tube?

There could be extra space inside the optical tube that is not contributing to the focal length. This could be done for better balance, weight distribution, or other similar design choices that has the focal length in a position where it is shorter than the overall optical tube. In the vast majority of cases, this will not be an issue ...

How long is a telescope tube?

If you see a telescope that has a focal length of 600mm (roughly 24”) and automatically assume that will be the length of the tube only to find out that the tube is actually 30” long, it could affect your plans for travel and storage.

How long is a 500mm focal length?

A focal length of 500mm is going to net you roughly 20” of length in imperial measurements which is less than two feet. These are all good things to keep in mind when reading about focal length.

Does focal length affect telescopes?

Other Ways Length Influences Telescopes. While it is a bad habit to immediately equate the focal length with the optical tube length, they are similar. That means that a telescope with a longer focal length is, by necessity, going to have to have a longer optical length.

What is focal length in astronomy?

Generally expressed, focal length is the distance (given in millimeters) between the telescope's primary lens or mirror and the point where the light rays come together in focus.

What to know about telescopes?

Knowing your telescope's limitations will help you to choose accessories, such as eyepieces and barlow lenses wisely. First let's learn about a telescope's focal length, and then we'll look at eyepiece focal length. Most telescopes list the focal length in the manufacturer specifications.

How to determine magnifying power of telescope?

How To Determine Your Telescope's Magnifying Power. Now that you understand the importance of your telescope's focal length, you can determine the magnifying power of any eyepiece you use in it. All it takes is a little math. Take a close look at your telescope's eyepieces and you'll see they also have a focal length.

What happens if you don't use a telescope?

If you aren't using a telescope with a drive unit, you will constantly have to use your slow motion controls to "track" your subject as the Earth moves. This can be very frustrating when viewing. Also, when you magnify, you are magnifying sky conditions ( How to Judge Sky Conditions ).

What does the focal length of a telescope mean?

The focal length of a telescope is defined as the distance (measured in millimeters) between the primary lens or mirror of the telescope and the point at which the light rays gather together to form a point of focus.

What can I see with a 700mm focal length telescope?

It is quite easy to observe every planet in the Solar System using a telescope of 70mm aperture. On the Moon, you will be able to get a close look at the surface and easily discern the majority of its distinguishable features and craters. Mars is going to look fantastic.

How do you find the focal length of an eyepiece?

If necessary, the focal length of the eyepiece (in millimeters) can be found by dividing 250 millimeters by the power of the eyepiece .

How do you find the focal ratio of a telescope?

Inputs for the Telescope Calculator: The Focal Ratio of the Scope (f/number) is: The ratio of the focal length of a lens or mirror to the aperture of the lens or mirror. An 80-mm-wide lens with a focal length of 400 millimeters, for example, corresponds to an f/5 focal ratio for a telescope.

What can you see with a 90mm telescope?

Enter the following information into the telescope calculator: Aspect Ratio (f/number) of the Scope of the Lenses The ratio of the focal length of a lens or mirror to the aperture of the lens or mirror An 80-mm-wide lens with a focal length of 400-mm, for example, has a focal ratio of f/5 when used with a telescope.

What is a good aperture for a telescope?

If you want to see as much as possible through your telescope, it should have an aperture of at least 2.8 inches (70 millimeters) or greater . Despite their inexpensive cost, Dobsonians, which are reflectors with a simple mount, deliver a large amount of aperture for a relatively little amount of money. A bigger aperture allows you to see fainter things and greater detail than you would be able to see with a smaller aperture.

What type of telescope is a Dobsonian?

A Dobsonian telescope (which utilizes a mirror rather than a lens) is similar in design to a Newtonian telescope in that it is a reflecting telescope (concave collecting mirror is at the rear of the telescope tube, eyepiece is on the side of tube, up near the front).

Schmidt-Cassegrain Telescopes

Long-focal-length scopes are ideal for imaging the Moon, planets, and the Sun (with an additional solar filter).

Newtonian Telescopes

While SCTs and MCs rule the roost for long focal lengths in a compact tube, a Newtonian reflector or a refractor can also serve dual purposes for deep-sky and long-focal-length work by using the previously mentioned tele-extender.

Comments

Typically people new to the hobby aren't ready to spend a few thousand out the gate on a massive mount and a large telescope plus a camera for imaging and tracking. You can get a reasonably priced Newtonian, but no reasonably priced mount is going to move it smoothly.

What is the focal ratio of a telescope?

The third key specification of a telescope is the focal ratio, which is the focal length divided by the objective diameter. A long focal ratio implies higher magnification and narrower field of view with a given eyepiece, which is great for observing the moon and planets and double stars.

How long is a telescope lens?

The focal length of the objective lens or mirror of a telescope will influence to some degree the overall length of a telescope. This 12″ telescope, which uses a large mirror to collect starlight, has a focal length of about 60″. So the overall length of the scope is quite long and can be unwieldy for some. Some modern scope designs use a clever optical layout to squeeze a long focal length into a small optical tube. This telescope has an 8″ (200 mm) mirror with an 80″ (2000 mm) focal length, but the light folds into a tube less than 20″ (500 mm) long. More about this type of scope in a later article…

What is the aperture of the objective lens of a telescope?

The aperture of the objective lens of this simple telescope is D. The focal length of the objective lens if F. The focal length of the eyepiece is f. So the magnification is F/f. The focal ratio is F/D.

How does a telescope work?

To get an image suitable for observing with our eyes, a telescope uses a second lens, or collection of lenses, called an eyepiece at the focal plane. The eyepiece magnifies the image from the objective. The eyepiece also has a focal length. The magnification of a telescope and eyepiece is very simple to calculate.

What is the magnification of a telescope?

The eyepiece also has a focal length. The magnification of a telescope and eyepiece is very simple to calculate. If the focal length of the objective is “F” and the focal length of the eyepiece is “f”, then the magnification of the telescope/eyepiece combination is F/f.

What is the aperture of a telescope?

Aperture also influences most of the other key specifications of a telescope, including practical (but non-optical) specs like cost and weight. A good backyard telescope for us amateur stargazers has an aperture of 80 mm to 300 mm (3.15” to 12”) or more.

How much magnification does a telescope need?

Another rule of thumb… the maximum useful magnification of a telescope is about 50x the aperture in inches. Any higher and the image gets too dim and fuzzy to be useful. So a 4-inch scope can get you about 200x before the image gets too fuzzy and dim, a 6-inch scope gets you 300x, and so on. This is not a hard-and-fast rule.

Optical Tube Length Versus Focal Length

Focal Length’s Effect on Imaging

• The general rule for focal length is the shorter the length, the wider the image. This plays a huge role in determining the focal ratio and goes into choosing a telescope that has an image angle that fits your style and goals or astronomy. While the focal length is only one part of the focal ratio, it is an important part, along with aperture. Gene...

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Other Ways Length Influences Telescopes

Millimeters to Inches