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TOPIC: Newbie Telescopes, Books


Posts: 131433
RE: Newbie Telescopes, Books

This happens to me all the time: I see something interesting up in the sky, a bright light, an interesting planetary configuration, a comet, a thin crescent moon, the Orion Nebula, etc. and Ill run inside and grab a pair of binoculars. As Im holding them up, neck craned upward, my arms start getting tired and the view through the eyepieces start to shake and move all over the place.
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Good reasons why lightweight or lowpowered binoculars are preferable.

My tips: An observing chair is great, but you may as well have set up the telescope (Doh!).
And to increase steadiness or relieve tired arms, another tip is to get lightweight binoculars or go to weightlifting classes. However, if you have an aversion to looking like Conan the barbarian then the simple tip of lying on a camping mat helps.



Posts: 131433
New Telescopes

Astro-physics has "officially" unveiled two new prototype telescopes. The first to be made available is the 140 mm f7.5 StarFire EDF which we expect to have out this summer. The second instrument, due out in late 2007 or early 2008 is the 130 mm f6.3 Traveler EDF which comes apart for packing into an overhead compartment sized case.

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Posts: 131433
RE: Newbie Telescopes, Books

Star gazing is my hobby and space my passion. I often go through the Internet to surf for great telescopes which allow me to have a closer look at the stars and other endless things in the Universe.
Here I have compiled a list of the best telescopes for personal use. There are many scopes available but I find these most appropriate to whet a stargazers appetite.

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Posts: 131433
Small Telescopes

The 60mm (2.4") refractor is the most popular telescope size for beginning astronomy enthusiasts and for casual gift-giving. This size telescope is perfect for introducing newcomers to astronomy, at an affordable price.
The simplicity of design, translates into reliability and ease of use, and requires little or no maintenance.
The refracting telescope will deliver excellent High contrast (due to no secondary mirror or diagonal obstruction) lunar, planetary and binary star views.
The usually sealed optical tube, helps protect the optics and reduce air currents, which tend to degrade image quality.

For astronomical observing, the 60mm refractor is large enough to see lunar details, Saturn and its rings, Jupiter and its moons, the phases of Venus, larger globular clusters, bright double stars and some bright nebulae. After adding an optional solar filter, you can observe activity on the sun. In addition, a 60mm telescope can be used for terrestrial viewing.
The small size and weight makes it very portable.

Limiting Stellar Magnitude 11.4
Resolution: Rayleigh 2.31arc seconds
Dawes Limit 1.93 arc seconds
Highest Useful Magnification 142x
Lowest Useful Magnification 9x
Light Gathering Power 73x unaided eye



Posts: 131433
Celestron Firstscope 70 EQ Telescope

70mm Refractor Telescope with Equatorial Mount
The Firstscope range offers novices in astronomy an economical entry into this oldest of sciences.
These are very upgradeable with many visual and photographic options.
This telescope has all glass components, coated optics and smooth functioning mounts, with the added benefit of slow motion controls on the mount for easy adjustments. The Firstscope 70 telescope tube is glossy black aluminium.
The German equatorial mount features setting circles and slow motion controls on the R.A. and DEC axes. These controls will enhance your viewing experience by simplifying both locating and tracking objects. When you're looking for a telescope offering a bit more versatility and control than the alt-azimuth models, these are the telescopes to consider.

Free Binoculars with this Product

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Posts: 131433
RE: Newbie Telescopes, Books

The UK retail stores LIDL will be selling the Meade LXD75 6-inch reflecting telescope with Autostar computer controller and mount and tripod for £499. It usually retails around £850.from the 30th November.

# Focal length:762mm
# Mirror diameter: 152mm
# Optical system: Newton reflector
# Magnification: 29x
# Finder scope: 6 x 30
# Super Ploessl eyepieces
# Price £499.00

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Posts: 131433
Bresser Skylux 70mm Equatorial Refractor

70mm f/10 Refractor (2-element achromat) Telescope with Equatorial Mount

The Bresser Skylux offers sharp high quality optics on a sturdy equatorial mount. This package is complete with all the accessories required to enjoy the night sky. Includes three eyepieces, viewfinder and erecting lens for daytime observation. An extremely versatile quality package for the discerning observer.

Eyepiece 4mm, 12mm and 20mm, (giving magnification powers of x175, x58 and x35 respectively), 5 x 25 Viewfinder, x1.3 Erecting Lens
Price £89.99
(£49.99 from Lidl stores)
Bresser Skylux 70mm
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-- Edited by Blobrana at 00:24, 2006-11-16



Posts: 131433

For an astronomer, binoculars may be very useful for several reasons: they are relatively inexpensive, have a large field of view and show images “right side up” (which makes finding things in the sky easier), are easily portable and require little to no setup.

So, how do you choose a good pair of binoculars for amateur astronomy?

There are different ways of categorising binoculars. But usually, they are distinguished by their magnification and the size of the aperture (for example, 8 x 42). A combination of a small magnification and large lens produces a brighter view. A 7x50 pair, for example, gives a brighter image than a 10 x 50, but the image magnification is smaller. A standard 7 x 50 pair is considered one of the best all-round binoculars for practicality, performance and price.

For high-powered observation, a magnification of 25x with a 100mm objective lens is recommended.
Observation binoculars come with either straight or angled eyepieces. The benefit of the angled design, usually 45º, is the ease of use and comfort of viewing. The angled eyepiece model is much more user-friendly, allowing more flexibility for people of different heights to use the binoculars without the need to continually adjust the tripod. It is also of benefit when the binocular is trained on the night sky. The straight eyepiece design model will require a higher adjustment of the tripod for each user and this may make the tripod less stable.
If you’re forced to go out to the country where you cannot fix your binoculars to something, then consider image stabilised binoculars. These are far more expensive but have other applications as well.
Stabilisation may be enabled or disabled by the user as required. Stabilisation will allow binoculars up to 20× to be hand-held. Major brands making 'image stabilised binoculars include are Canon, Nikon, and Bushnell.

Digital binoculars are becoming increasingly popular - these capture a digital image seen through the binoculars.
Zoom binoculars have the facility to quickly and very efficiently zoom in on the object of interest, but the image quality is compromised in cheaper models. The extra workings and glass inside reduce the amount of light available, making them unsuitable for astronomy.
Avoid binoculars that claim to be "focus-free". Also be beware of advertising lingo like "high-powered". Increasing the magnification will decrease the brightness and field of view, which makes objects faint and fuzzy.
A lower magnification will maximise the amount of light transferred.

The larger the aperture, the brighter the image will be; but the greater the size, the binoculars will weight and cost more. For general astronomy use, choose binoculars with an aperture of 50mm. An observation binocular with a 60mm objective lens will still be fairly portable whilst an observation binocular with a 80 to 100mm + objective lens is far more suited for static use.
The size of the objective lens and the power of magnification are the two major factors that determine the light transmission of the binocular. For example, 100mm (the diameter of the objective lens) divided by 25 (the power of magnification) gives a figure of 4, which is the diameter (mm) of the exit pupil and indicates the amount of light reaching the eye. In general the larger the exit pupil diameter the brighter the binocular will appear and the better the resolution will be, enhancing colour and contrast perception, especially in low light conditions. However, as the human eye pupil dilates on average from 2.5mm to 7mm depending on light conditions it follows that an exit pupil above 7 is not beneficial as the human eye cannot accommodate it.

It is worth remembering that as we age our eye pupil does not dilate so much, so a large exit pupil of 7mm is not so important for a 50 year old person compared with a 19 year old. So a 4mm exit pupil on a 25x100 observation binocular will be more than satisfactory for most users in most conditions, whereas a 40x100 will only give 2.5mm exit pupil, drastically reducing the amount of light reaching the eye.
10x50 or 8x40 will have a 5mm exit pupil.
A standard 7x50 pair will have a 7mm exit pupil, the average human eye pupil size at night.

Most binoculars are not suitable for use with glasses (spectacles). You have to put your eye close to the eyepiece, but the glasses prevent you from getting close enough. You can of course take your glasses off to use the binoculars, but this can be a nuisance. It is possible to buy special binoculars which can be used with glasses.
Standard binoculars have eye relief ranging from only a few millimetres to 15 millimetres.
Long eye relief (15 to 25 millimetres or more) is necessary for eyeglass wearers. A poorly designed optical system may force the observer to press his or her eye close to the eyepiece in order to see an unvignetted image, or alternatively may have an exit pupil larger than the observer's pupil at a comfortable viewing position, resulting in wastage of light and a dimmer image.

The eyepieces of binoculars are usually permanently mounted in the binoculars, causing them to have a pre-determined magnification and field of view. Normally binocular eyepieces are 3-4 element with marginal correction for colour and edge sharpness. The correction on Siebert 6 element eyepieces are comparable to a Japanese made Meade 26mm Super plossl. The eyepieces do not add colour correction or false colour.
Wide-angle binoculars have a field of view that is wider than average (60 or higher).
The Field-of-view is the size of an area that can be viewed using the binoculars.
Binoculars are advertised with their field of view specified in one of two ways: angular field of view, and linear field of view. Angular field of view is typically specified in degrees, while linear field of view is a ratio of lengths. For example, a pair of binoculars with a 5.8 degree (angular) field of view might be advertised as having a (linear) field of view of 305 feet per 1000 yards or 102mm per meter. As long as the field of view (FOV) is less than about 10 degrees or so, the following approximation formulas allow one to convert between linear and angular field of view. Let A be the angular field of view in degrees. Let L be the linear field of view in feet per 1000 yards. Let M be the linear field of view in millimetres per meter. Then:

A = 0.0191 \times L
A = 0.0573 \times M
L = 52.4 \times A
M = 17.5 \times A

Generally, higher powered binoculars give you a smaller field-of-view and the opposite is true for lower powered binoculars. Field-of-view may also be expressed in two ways; as the width in feet at 1,000 yards, or in degrees of field. When expressed in feet the field is called linear, and when expressed in degrees it is called angular. To convert angular field to the more practical linear field, multiply the angular field by 52.5.
For astronomy, a wide field of view is desirable because if offers a more pleasant viewing experience, and you can see more of the sky at a better edge performance compared to a narrower field.

Binoculars use prisms to provide correctly oriented images, and to shorten the optical path.
The typical binocular design can be porro-prism or roof prism.
The size and design of the prisms will affect sharpness, with quality optical glass delivering clarity from edge to edge of the field of view (sometimes called a "flat field").
Porro-prisms have objective lenses that are spaced farther apart than the eyepieces. Porro-prisms are bulky but usually perform better and cost less then roof-prisms. Porros yield a better three-dimensional image. Roof-prisms dominate the consumer market. The objective lenses line up directly with the eyepieces, resulting in a streamlined, compact and lightweight binocular. But roof-prisms usually cost more and lose more light to reflection, which is a disadvantage for astronomers but not for daytime terrestrial viewing.

Prisms are located inside binoculars that are like mirrors. It is a reflective coating on glass that bends and refracts light to bring the subjects you are looking at to your eyes. The BAK-4 prism is made of a high quality glass and produces sharp images and good edge to edge sharpness. Generally, higher quality binoculars will use BAK-4 prisms in the construction process. Phase coated prisms have a coating process that enhances the resolution and contrast of images coming through the binocular and are generally applied only on more expensive binoculars.
If the prisms are made of BaK-4 Barium crown glass the exit pupils will be round and evenly illuminated. If the prisms are of BK-7 Borosilicate crown glass you will notice squarish, grey edges in the exit pupils.

Roof Prism System
In roof prism binoculars the prisms overlap closely, allowing the objective lenses to line up directly with the eyepiece. The result is a slim, streamlined shape in which the lenses and prisms that magnify and correct the image are in a straight line. An Abbe-Koenig prism is a type of reflecting prism used to invert an image (rotate it by 180°). The prism is named after Ernst Abbe and Albert Koenig. The prism is made from two glass prisms which are optically cemented together to form a symmetric, shallow V-shaped assembly.
A Schmidt-Pechan prism is a type of optical prism used to rotate an image by 180°. They are commonly used in binoculars as an image erecting system.
The prism consists of two glass prisms separated by an air-gap. Multiple total internal reflections of the light cause a vertical flipping of the image; a "roof" section of the second prism also flips the image laterally, together causing a 180° rotation of the image. The image's handedness is not changed.
Compared to the double-Porro prism or Abbe-Koenig designs, the Schmidt-Pechan is much more compact. However, the large number of reflections and glass/air transitions of the light make the prism more lossy than the other designs. Some of the surfaces must be optically coated for efficient internal reflection, since the light is incident at an angle less than the critical angle.
The multiple internal reflections also cause a polarisation-dependent phase-lag of the transmitted light, in a manner similar to a Fresnel rhomb. This must be suppressed by special phase-correction coatings to avoid unwanted interference effects on the image.
Phase-corrected prism coating and dielectric prism coating are recent (in 2005) effective techniques for reducing reflections. Light reflected from one roof surface is 1/2 of a wavelength shifted from the light hitting the other roof surface, sometimes referred to as "out of phase" or "phase shift". Although the light waves are subsequently forced back together when they reach the viewer's eye, this phenomenon results in reduced contrast and image resolution. This effect does not occur in Porro prism designs.

Porro Prism System
In porro prism binoculars the objective or front lens is offset from the eyepiece. Porro prism binoculars provide greater depth perception and generally offer a wider field of view. A Porro prism binocular will inherently produce an intrinsically brighter image than a roof prism binocular of the same magnification, objective size, and optical quality, as less light is absorbed along the optical path. However, as of 2005, the optical quality of the best roof-prism binoculars with up-to-date coating processes as used in Schmidt-Pechan models is comparable with the best Porro glasses.

Of course, you will want to consider the following factors:
* Price: pay for the features you get and don’t pay for the ones you don’t want
* Coatings: reduce glare, and protect against water and other potential damage
* Quality of construction: the grade of glass, the quality of the prisms and the material used in the barrel are just a few of the factors to be mindful of. BK-7 borosilicate flint glass are of lower quality; for optimal optics, make sure you have BaK-4 barium crown glass prisms
* Long eye relief is a worthwhile feature for eyeglass wearers.

Chromatic aberration is caused because light of different colours does not bend the same amount when passing from glass to air. Blue light, for example, will not focus to the same plane as red light. The effect can create a "ring" of colour around point sources of light, and results in a general blurriness to the image. Chromatic aberration is minimised by using an achromatic doublet (or achromat) in which two materials (usually crown and flint glass) with differing dispersion are bonded together to form a single lens. This reduces the amount of chromatic aberration over a certain range of wavelengths, though it does not produce perfect correction.
The problem can be reduced in several ways. One method is to apply a thin film to the eyepiece element that corrects. The more traditional approach, however, is to eliminate the aberration by using multiple elements of different types of glass and curvature.
An apochromat is a lens or lens system which has even better correction of chromatic aberration, combined with improved correction of spherical aberration. Apochromatic lenses are designed to bring three wavelengths (typically red, green, and blue) into focus in the same plane. Apochromats are much more expensive than achromats.

Antireflection coatings lens coatings reduce the amount of light reflecting off of the lens and allow more light to pass through. Without coatings, up to 50% of the light entering the binoculars is lost to reflections from the many glass surfaces within. The more expensive brands will have multiple coatings on ALL the lenses which will help to give the brightest and clearest images.
The most used and least expensive coating is a single-layer of magnesium fluoride (MgF2), but there are also modern broadband multicoatings. Magnesium fluoride, which is also hard-wearing, reduces reflections from 5% to 1%. Modern lens coatings , such as zinc sulphide or titanium dioxide, consist of complex multi-layers and reflect only 0.25% or less to yield an image with maximum brightness and natural colours.
To save money, some optics manufacturers coat only some of the air-to-glass surfaces.
Common Antireflection coatings often look somewhat bluish (since they reflect slightly more blue light than other visible wavelengths), though green and pink tinged coatings are also used.
Binoculars that have so-called "ruby" coatings intended to reduce glare in bright light and improve the contrast between brown and green objects. Avoid any binocular that uses these coatings, it will perform poorly for astronomical use.
But generally, as far as binoculars go, better coatings mean higher cost!

Coating symbols:

Coated (C) - One or more surfaces are coated.
Fully-Coated (FC) - All air-to-glass surfaces are coated but plastic lenses may not be.
Multi-Coated (MC) - One or more surfaces are coated.
Fully Multi-Coated (FMC) - All air-to-glass surfaces are coated.

Binoculars come with two types of focusing mechanisms. Most people opt for the centre-focus model, which uses a centrally mounted wheel to adjust both eyepieces at once. There is also a separate adjustment for the right eyepiece, which helps to correct for any difference in near or farsightedness between your eyes.
The second focusing system uses individually focused eyepieces and has no centrally located focusing mechanism. Even though focusing is slower compared to the previous model, binoculars that use individual focus tend to be more rugged and less prone to moisture infiltrations.

Hermetically sealed binoculars filled with dry gas (usually nitrogen) will not be susceptible to clouding due to condensation at low temperatures; this will also help to prevent mildew, although air may leak in over a period of years if the binoculars are not overhauled.

Modern binoculars have a hinged construction that enables the distance between eyepieces to be adjusted to accommodate viewers with different eye separation. This adjustment feature is lacking on many older binoculars.

Because binoculars are basically two small telescopes mounted side by side, an error in collimation (optical and mechanical alignment) can lead to numerous problems including eyestrain and double-images. For most binoculars collimation problems are not immediately obvious when you first pick the instrument up and view through it. If after using the binoculars for several minutes your eyes feel uncomfortable as they compensate for the barrel misalignment, most probably the binoculars are out of collimation, which means that the two barrels don't point in the same direction. This is a serious problem, and you shouldn't buy those binoculars.

Keep your binoculars in their protective carrying case to prevent dust and grit getting into the mechanism. This can clog up the oils and make the controls grind which could eventually seize up. Also avoid knocking them-prisms are often mounted lightly and a bump can misalign one, causing double vision. For the best view keep the front and rear lens surfaces clean with optical cleaning fluid and a soft lint free cloth.

The following gives a guide as to what to expect to pay:

8x30 binoculars from £30
7x50 binoculars from £49
10x50 binoculars from £49
20x80 binoculars from £450

With the 20x80 binoculars you will need a tripod stand, which may cost around £50.



Posts: 131433

For a novice amateur astronomer, binoculars may be very useful as a first instrument for several reasons: they are relatively inexpensive, have a large field of view and show images “right side up” (which makes finding things in the sky easier), are easily portable and require little to no setup. For more experienced amateurs, they may still be useful for most of the reasons mentioned above, even for those who have (or have access to) more powerful instruments. So, how do you pick good binoculars for amateur astronomy?

Binoculars are basically two small telescopes mounted side-by-side, with a set of internal mirrors and prisms that cause the images to be seen right-side-up and non-mirrored. There are two "models" of internal prisms: "roof" prisms are those used in "straight" binoculars, in which the objectives are exactly aligned with the eyepieces and the optical tube is straight, while "Porro" prisms cause the objectives to be more separated than the eyepieces and the optical tube not to be straight (that is the format that most people think of when thinking of binoculars).
Functionally there is almost no difference between the two models, although Porro models tend to give you a wider filed of view, while roof models can be more compact than Porro models (and tend to be more expensive).

Binoculars are primarily identified by two numbers; for example, 7×50 or 10×40. The first number denotes the magnification achieved by the binoculars, while the second is the size, in millimetres, of the objective (front) lenses. Both numbers are important, and are a good starting point to pick the best possible instrument.

First, magnification, or power. That indicates how much larger an image will appear than if you were just using your eyes. It may seem that the larger this number is, the better, but that is not necessarily so. For astronomy use, unless you intend to use a tripod, magnifications between 7 and 10 are the most indicated. Anything over 12 will cause the image to shake way too much, unless the instrument is stabilised (by a tripod, for example).

Now, lens size, or aperture. The reason this number is important is that it tells you how much light the instrument gathers. Binoculars not only magnify the objects you’re seeing, they also act as larger light receptors than your eyes. Your pupils, when you’re in a dark location and fully adapted to the light conditions, will have a diameter of between 5 and 7 millimetres (the younger you are - as an adult -, the closer to 7mm it is; as you get older, it gets smaller).
Since the light gathering ability is defined by the area of the objective, a 50mm binocular will gather over 50 times more light than your naked eyes. This will increase your limiting magnitude by around 4, under dark conditions (from 6 to 10, for example).

As a general rule, any aperture smaller than 40 millimetres in useless for astronomy; you simply will not get enough light into your eyes. 50 is a good size; anything much larger will be, well, too large and too heavy for comfortable use. It will be significantly more expensive, as well.

Power and aperture together define another interesting measure: the exit pupil. That is the size of the image that is formed on the eyepiece and that, ultimately, is delivered to your eyes; you can get this size by dividing the aperture by the magnification power (for a 7×50 binocular, the exit pupil will be 50/7 = 7.14mm). Ideally, this should be exactly the same size as your dark-adapted pupil or very slightly smaller, so that your whole pupil is used in collecting light and no light is wasted. Since pupils are not all the same size, this is clearly impossible; you should shoot for an exit pupil in the range of 5 to 7mm.




Posts: 131433
RE: Newbie Telescopes, Books

In that price range there is very little to choose between them. But I would tend to go for a decent 80mm refractor (or bigger); I would also be on the look out for any bargains in the `sales` that should be happening at this time of year.

The skywatcher telescopes, if you can find them over where you are, offer a decent beginners telescope.

£109 ($200.00)
(did you follow that webpage link?)

But if you want to do a bit of photography , a reflector is a must but they will be a bit more pricey.

Just remember not to get hung up on how much "power/ magnification " a telescope has. What you really need to look out for is the size of the front lens, or its aperture - that is, the amount of light your telescope can collect. The larger the telescope is, the dimmer the objects you can see.

Another thing to consider is portability. A giant eight inch telescope needs extra careful handling and set up time, while a 3” refractor can just be carried in a rucksack and has a quick setup time.

If you are like me, and just want to scan the skies for all sorts of objects like deep sky nebulas, galaxies, or comets then a short focal length will do. But for lunar / planetary observing then you need a long tube telescope (long focal length).
It's up to you.

But check out this ShortTube™ 80mm Refractor $179.00
You will need a tripod with this remember! (standard camera tripod will do)

Or this if you haven`t got a tripod already:

Observer™ 70mm EQ Refractor
This is the one i would go for, with it`s mount and controls knobs...

-- Edited by Blobrana at 21:07, 2005-07-26

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