Here you’ll find answers to popular questions and general knowledge
There are different telescopes for different purposes. Telescopes vary in type, size and shape, each model offering its own unique features and benefits.
Refractor Telescope: Uses a sealed tube that reduces in width, with a front glass lens called the objective lens that refracts light to the back of the tube. You look into the eyepiece from the rear of the telescope.
Reflector (Newtonian):
The reflector design uses an open tube with a rear internal mirror called the primary mirror.
The Primary mirror reflects the light / image back to smaller secondary mirror.
The secondary mirror is mounted internally close to the top of the tube, this mirror reflects the light out to the side of the telescope
You look into the eyepiece from the top side of the telescope.
Cassegrain (Schmidt):
The Schmidt design has a front corrector plate that is aspherical lens. This lens is not flat and is costly to manufacture.
Light enters the front corrector plate and is corrected for spherical aberration before reflecting off the primary rear mirror back towards the secondary mirror on the rear of the corrector plate.
The light / image then reflects off the internal secondary mirror back towards the rear of the telescope, through the center of the primary mirror and out into the eyepiece.
The secondary mirror on the rear of the front corrector plate (front lens) is adjustable for collimation on a Schmidt design.
Cassegrain (Maksutov):
The Maksutov design has a front corrector plate that is meniscus lens. This lens is not flat, however it is a lot easier to manufacture than a Schmidt design.
Light enters the front corrector plate and is corrected for coma and chromatic aberration before reflecting off the primary rear mirror.
The secondary convex mirror reflects the light / image back to the rear of the tube, through the center of the primary mirror, into the eyepiece.
This design also has a secondary mirror on the rear of the front corrector plate (front lens) that is convex. This is not a adjustable secondary mirror which simplifies the telescopes construction. This secondary mirror is also known as a “silvered spot”.
Every telescope has a focal length, which is length from the front lens or primary mirror to the eyepiece lens. The magnification is the focal length divided by the eyepiece focal length. Eg, 1000mm / 10mm = 100X magnification.
Aperture is the diameter of the primary lens or mirror, normally provided in millimeters (mm). A larger aperture allows for more light to be captured and provides brighter views, better contrast and more detail. Also, the larger the telescopes aperture, the greater magnification possibilities.
A telescopes focal length is the length light travels inside the telescope.
This is measured from the front lens / mirror to the focuser / eyepiece exit.
The shorter the focal length, the wider field of view and lower magnification capabilities.
The longer the focal length, the higher magnification and reduced field of view.
Resolution is the telescopes ability to resolve detail of object you are looking at.
Resolution is improved with a larger aperture and is provided in arc seconds.
Higher resolution is important when you want your telescope to visually separate double stars or see fine detail on the moon or planets.
A larger aperture or higher lens quality will improve resolution.
A smaller telescope with low magnification, aligned with the main telescope to assist and simplify finding night sky objects.
This can include a crosshair or battery powered illuminated red dot to help you centre the planet or star, making it easy to find when looking through the telescope at high magnification.
Mirrors and lenses can be coated with high quality chemical or physical elements to improve:
The higher quality of coatings, the higher the cost of the lens or mirror and so the telescope.
A Barlow lens is a lens (diverging lens) which is placed into the telescope focuser before the eyepiece.
The Barlow lens will decrease the eyepieces focal length, in which increases the magnification of your eyepiece
Most common barlow lens sizes are 2x or 3x.
Upgrading your eyepieces will offer a huge improvement in viewing pleasure and can be done at any stage of your astronomy journey and be kept and used with new telescopes you may purchase in the future.
Allows the telescope to move left and right, and up and down. Ideal for beginners first telescopes and using the telescope for land viewing. Computerised Go-To tracking / GPS telescopes use Alt Azimuth mounts. It is common for the user to have to move this telescope by hand, some alt-azimuth tipods include slow motion controllers.
Allows the telecope to move in-line with earths rotation. Requires alignment with the South Celestial Pole. Ideal for astronomy viewing as earth rotates.
It is common for this mount to have slow motion controllers, allowing the user to keep track of the object for longer periods.
Uses a Reflector type tube system with a lower cost, simplified mounting base to allow for a larger mirrored telescope at a similar price to a tripod mounted equatorial telescope. The dobsonian mount moves in the Alt Azimuth configuration.
A convenient tray, normally located under the telescope base, inside the tripod mount.
An ideal place to store your eyepieces, filters and other telescope accessories.
Remember you will want to find a very dark spot outside when using your telescope, having all your accessories close will help you maximise your viewing time and experience.
Vibration isolation pads are an accessory you can purchase to place under the telescopes tripod legs.
Even the smallest amount of wind or a non stable surface with footsteps can create small vibrations that shake the telescope, when viewing through the telescope, these vibrations will shake your image, interrupting your viewing.
Vibration pads dampen movement which will improve your viewing and photography experience
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Some equatorial model mounts can have optional motors attached to them to allow you to track objects and maneuver your telescope, these are called motor drives.
Most common is a single motor drive on the right ascension to allow for tracking to compensate for earths rotation.
Some equatorial mount will also allow for two motor drives to be connected, this is dual axis motor drives.
High quality motor drive upgrade systems can also include a hand controller to upgrade your mount to a GoTo tracking computerized telescope.
Always check your mount model and features before purchasing any upgrades
Binocular (Roof Prism):
Binocular (Porro Prism):
Binoculars consist of system of lens and prisms that allows light to enter via a larger objective lens at the front. Light then travels through a prism and then out of the eyepiece lens to which we can hold to our eyes.
During this process the image is magnified so we can see the resulted image larger than with our naked eyes.
The Objective lens is the large lens at the front of the binocular.
The objective lens is a converging or convex lens which allows the light to refract towards the smaller lens called the eyepiece lens.
A convex lens is thicker in the middle of the lens, than at the outer edges.
A Porro Prism is rectangular faced,triangular glass shape.
An image / light traveling through a Porro Prism is rotated by 180 degrees.
Light enters the larger longer rectangular side and undergoes internal reflection twice then returns out via the same face it entered.
Porro prisms are often used in pairs with the second prism rotated a different orientation from the first.
Used in a binocular to erect the image.
BAK4 Prism is a type of Porro Prism design with a higher quality optical glass.
The glass used it called Barium Crown glass and is produced from alkali lime silicates containing potassium oxide.
Barium Crown glass has the following features / benefits:
Lower quality binoculars often use BK7 glass.
A roof prism a reflective prism containing a section where two faces meet at a 90° angle, resembling the roof of a building.
When light / image travels through a roof prism it undergoes multiple internal reflections.
The image will exit flipped / revered to the input image.
8 = 8x magnification
The object you are looking at will appear 8c closer.
42 = The diameter in millimeters of the objective lens (front lens).
8×42 is a popular size, the larger the objective lens the more glass and heavier / bulkier the binoculars.
The smaller the objective lens, the smaller and lighter the binocular. However, the less light will pass through, reducing the brightness, clarity and sharpness of the image.
The Field of View is the width / angle of your vision visible through your binocular.
This width is most commonly provided in degrees, for example a common 8×42 binocular will have a 6 – 7 degree FOV.
The higher the magnification or smaller the objective lens, the narrower the field of view.
The exit pupil is the visible round circle that exits the eyepieces and is noticeable when you hold the binoculars away from your face and look into the eyepiece lens.
This circle of light is measured in millimeters and is calculated by dividing the objective lens size by the binoculars magnification.
For example, a binocular with the size 10×42 will give you a 4.2mm exit pupil.
The human pupil will vary in size from 2 to 7mm depending on the brightness of the location. In brighter conditions the exit pupil can be smaller and larger for darker locations.
Eye relief for binoculars is the length/distance of the eyepiece lens to your eye.
A longer eye relief is preferred when you require to wear glasses, allowing extra distance to view more comfortably.
If the eye relief is too short you may experience vignetting which is when the image is reducing in brightness / visual quality around the outside areas of you view.
Most binoculars will have two focusing options, the main focus method is the center focus ring. rotating this focus ring will change the internal distance between the eyepieces and the objective lens.
Adjusting the center focus will focus both eyepieces simultaneously.
The secondary focus option is called the diopter adjustment and this is to make small adjustments for the difference in our left to right eye.
The diopter focus adjustment is most commonly made by adjusting one eyepiece, to make this adjustment you will need to close your opposite eye while rotating the eyepiece to achieve a clear image.
An eyecup is the rubber structure around the eye piece lens that you rest your eyebrows on.
Most eyecups are a rubber for comfort, grip and waterproofing and can also be adjustable by rotating out and in to help seal your vision into the eyepiece from unwanted light.
The diopter focus adjustment is most commonly made by adjusting one eyepiece, to make this adjustment you will need to close you opposite eye while rotating the eyepiece to achieve a clear image.
The diopter focus is there to make small adjustments for the optical differences in our left to right eye.
When looking up into the dark night sky, you want to maximize the brightness to achieve the best viewing of all the faint astronomical objects.
To get these results you would want to go for a low magnification binocular with a large objective lens, a popular size is the 7×50.
7x Magnification and 50mm objective lens size, this model would give you a large exit pupil size of 7mm.
A benefit of lower magnification is the ability to hold the image steady when looking up to the sky. A higher magnification, the more shaking is noticed and you could require a tripod for extra stability
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The popular binoculars for bird watchers are the 8×42 and 10×42 models / sizes in a roof prism design.
Many manufactures will offer these sizes in a variety of quality levels, improving the optics and waterproofing as the models increase in value.
These two sizes are not the largest or smallest types of binoculars on the market and offer a good level of brightness and detail due to the average magnification and large lens size.
Birdwatchers need to consider many things when observing and walking such as:
If its your hobby and you are investing a reasonable amount of your spare time on bird watching, we suggest you consider going for the highest grade binocular in these sizes you can afford.
Prisms and lenses can be coated with high quality chemical or physical elements to improve:
Multi coated is when the optics are coated in more than one of these exotic elements, improving the lens performance with each additional coating.
The higher quality of coatings, the higher the cost of the lens or mirror and so the Binocular.
Under Construction
Every telescope has a focal length, which is length from the front lens or primary mirror to the eyepiece lens. The magnification is the focal length divided by the eyepiece focal length. Eg, 1000mm / 10mm = 100X magnification.
Is the diameter of the primary lens or mirror, normally provided in millimeters (mm). A larger aperture allows for more light to be captured and provides brighter views, better contrast and more detail. Also, the larger the telescopes aperture, the greater magnification possibilities.
Resolution is improved with a larger aperture, and is provided in arc seconds. It is important when you want your telescope to visualy seperate double stars or see fine detail on the moon or planets.
Mirrors and lenses can be coated with high quality chemical or physical elements to improve light transmission/brightness and detail/clarity and reduce reflection. The higher quality of coatings, the higher the cost of the lens or mirror and so the telescope.
A smaller telescope with low maginification, aligned with the main telescope to assist and simplify finding night sky objects. This can include a crosshair or battery powered illuminated red dot.
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