Vixen Optics

 

 

How to choose a
Telescope, Binocular or Mount


How to Choose the right binocular.
 

Magnification:

Magnification is the most important factor in choosing binoculars. Magnification up to 10x is appropriate for viewing without a tripod. The views seen with magnification higher than 10x can become shaky due to the vibration caused by holding it in your hands. It will also produce a darker image and narrower field of view. The magnification of a field scope can be varied by changing the eyepiece. Choose binoculars with the best magnification according to your need. For magnification higher than 10x, use a tripod or try to secure your position by supporting your hands.

Objective Lens Diameter:

The larger the objective lens diameter, the higher the light gathering power and resolution of the binoculars or field scope. A large objective lens results in a clear image. The binocular body becomes larger as the objective lenses become larger making it less portable.

Real Field of View:

The "Real Field of View” is expressed in the angle in which you can view without moving from your position. The wider the real field of view, the wider space you can view. Choose a model with a wide real field of view for viewing fast moving objects such as birds or sports events. Choose a model with an Ultra Wide field of view, 75 degrees or more, for viewing large areas, such as the Milky Way.

Eye Relief:

“Eye relief” is the distance between your eyes from which you can view the entire field of view through the eyepiece and the eyepiece lens surface. A design with long eye relief makes it easier for viewing even with eyeglasses. A model with long eye relief causes less strain during long observing sessions.

Size:

The size of the model with a superior optical performance generally tends to be large. Choose a model which suits your need by considering your carrying method and observing location.

Lens Coating:

Various coatings are applied on the surfaces of lens and prisms. The coating reduces the loss of light, thus it produces a bright image. The optical performance depends on the type of coating and the optical surfaces applied. PFM coating, which applies multi-layer coating on all the lenses and prisms, provides an excellent optical experience.

  • Fully Coated: Coating is applied to all surfaces of lenses to decrease loss of light.
  • Multi Coated: One or more of the lenses are coated with 3 or more layers to increase light transmission
  • Fully Multi Coated: All air to glass surfaces are coated with multiple layers to achieve high contrast images
  • PFM Coating: Perfect Full Multi Coating minimizes the loss of light transmission resulting in bright sharp images
  • Flat Multi Coating: Advances seven layers of anti reflection coatings are applied to the surfaces of the lenses to uniformly minimize light loss over the spectrum of visible light.
  • Phase Coating: Special coatings are applied to correct for phase shift of roof prism binoculars to enhance resolution and contrast.
  • High Reflectivity Coating: Dielectric Coatings are applied to maximize the reflection of roof prism binoculars to produce clearest, brightest images.

ED Lens:

Extra Low Dispersion glass is used in the objective lens to eliminate chromatic aberration, providing a high level of color correction and a crystal clear view.

There are “fixed magnification,” which allows you to view only in one magnification and “zoom,” which allows you to vary the magnification by moving the zoom lever. The eyepieces installed in field scopes are also divided into “fixed magnification types” and “zoom types.” The zoom type, in which the magnification can be varied according to what object you are viewing, has a wide range of uses. A field of view produced by zoom types with a higher magnification is narrower and darker compared to that produced by a fixed type.

Waterproof:

Nitrogen gas filled optics provide a waterproof design which can be used in rain or snow.Choose a waterproof binocular or field scope if you are using them in a location where your optics are likely to get wet.

TERMINOLOGY

Digiscoping

Process of photography using our digital camera and a spotting scope. Choose the right adapters for your models.

Apparent Field of View
How wide the field of view looks when viewing through the binocular is expressed as an angle.
“Apparent Field of View” = “Real Field of View” x “Magnification”

Field at 1000m
The field range seen at 1000m without moving the binoculars is expressed in meters.

Exit Pupil
Expresses a diameter of the image of the object lens produced by the eyepiece. The larger the exit pupil, the brighter the image.“Exit Pupil” = “Objective Lens Diameter” # “Magnification”

Brightness
The number obtained by squaring the exit pupil is the “brightness.” The larger the number, the brighter the image.

Near Focus
It is expressed as the shortest distance between the binocular and an object in focus. (It varies according to the eye vision of an individual.)

Types of Prisms
In the "Porro prism" design a combination of right angle prisms are used. These binoculars are sturdy and provide outstanding performance for the price. The "Roof Prism" . binoculars provide excellent performance but the body tends to be large. The roof-prism binoculars are more compact than Porro-prism binoculars with the same aperture size. They are designed so that the lenses and prisms are in a straight line.

Types of Spotting Scopes
Spotting scopes are either 45 deg angled view or straight thru design. The angles view is most convenient when viewing objects above you. The straight thru design allows you to easily keep your target object centered in the spotting scopes field of view.
How do I choose a telescope?
 
Optical Tube
Optical tube is the main component of an astronomical telescope as it contains the lens and mirror that collects light from celestial objects and the eyepiece lens that magnifies the image.
The factors that determine the performance of an optical tube are:
・The effective diameter of objective lens (primary mirror)
・The performance of lens or mirror

An objective lens (primary mirror) with a larger effective diameter size can collect more light and forms a clearer view of faint and hard-to-see objects. The performance is largely affected by the material of the lens or the mirror and precision employed in manufacturing.

Refractor Telescopes

The image formed by the light rays passing through the objective lens is magnified when they pass through the eyepiece lens.
• Constantly stable field of view, suitable for observation of any astronomical object.
• Maintenance during storing is not particularly necessary; It is easily maintained.
• Relatively expensive among other types of optical tubes with the same aperture size.
• Heavier than the other types of optical tubes due to the multiple lenses used.

Reflectors (Newtonian) Telescopes

The light reflected off the primary objective mirror (concave mirror) is then reflected off a tilted mirror and finally passes through the eyepiece lens causing the image to be enlarged. The eyepiece lens is placed on the side of the optical tube.
• Sharp central images, no chromatic aberration (no color is seen around the corners of images).
• An optical tube even with a large aperture is moderately priced.
• A large difference in temperatures between outside and the tube could create air turbulence. The tube temperature must be adjusted to outside temperature before making any critical observation.
• Is not usable for observation of the Sun.


Catadioptric Telescopes

This configuration takes components of both refractors and reflectors.
• Chromatic aberration, coma aberration, spherical aberration, and field curvature are all corrected accurately.
• Compact and lightweight; convenient for carrying and observing.
• A large difference in temperature between outside and inside the tube could create air turbulence. The tube temperature must be adjusted to outside temperature before making any critical observation.
• Not applicable for observation of the Sun.

What are the types of telescope mounts?
  .
Altazimuth Mount
– Tracks a celestial object by combining movement of both the vertical and horizontal motions.
The altazimuth mount has simple vertical and horizontal motion controls designedto easily point a telescope to the object you wish to view.

• Can be assembled and handled easily due to its simple structure.
• No setting such as polar axis adjustment done for equatorial mounts is necessary. You can quickly prepare for observation.
• Lightweight and portable.
• Can also be used to mount a terrestrial telescope.
• Not recommended for long-term observation at powers higher than 100x.
• Not designed for long exposure astro-photography.

Equatorial Mount
– Tracks an object in accordance with the rotation of the earth.
The direction of the optical tube is adjusted by an arc motion just as the constant diurnal motion of a celestial object. Mounts may have motors for tracking or hand controllers for Go To functions

• Allows tracking of an object over an extended period.
• Suitable for long observation at high powers or for astrophotography.
• Mounts with various functions such as automatic object search and automatic tracking are available.
• For beginning observers, usage of equatorial mounts is not as intuitive as that of altazimuth mounts. Beginners should read the manual thoroughly.
• The polar axis must be adjusted before beginning observation.
• Heavier than altazimuth mount.

What should I consider when buying a first telescope?
  For children, a telescope which your child can move freely and operate on her own would be a good choice. A model that is lightweight and simple to handle would be best. As interest grows, you can “graduate” to larger mounts and optical tubes. Try to start with a system that can be upgraded without buying a completely new setup.Consider a mount with a simple hand controls that allows you to choose manually track objects. This will be a lightweight system, easy to use and easily transported to any location.
Best products for Astrophotography.
  There are a few options for astro-photography.

For Wide Field Astrophotography, you can select a tracking mount for your DSLR Camera. This includes Vixen's Polarie Star Tracker and the GP photo guider.

If you are interested in doing prime focus photography or eye projection photography by connecting a camera to the telescope, you will need an equatorial mount which will perform auto-tracking of celestial objects. An equatorial mount is a must for the avid photographer. By tracking your target object, it eliminateds star trails and allows you to take amazing images. Mounts with precise tracking motors are needed. An added feature is GOTO. Mounts with built in star chart controllers allow you to find objects with ease and will accurately track for long exposures.

For the optical tube, your viewing site and accessability are factors. Refractors with ED Glass with its stable field of view will deliver high contrast images of planets and more . Reflectors will also deliver great views of nebulas and star clusters. Some telescopes are designed for the astrophotographer, such as Vixen's VC200L and R200Ss.

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