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.
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.
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.
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”.
Common Terms & Meanings
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:
- Light transmission
- Brightness / Contrast
- Reduce reflection.
The higher quality of coatings, the higher the cost of the lens or mirror and so the telescope.
The eyepiece is a glass lens module which comes in a variety of types and lengths.
Most filters attach buy screwing directly to the bottom of your eyepiece or clip into the end of 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.
- Improved detail
- Wide Angle
- More or less Magnification
- Zoom magnification
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.
Tripods & Mounts
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
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