Glossary of common terminology

A

Alt-Az Mount: Short for Altitude-Azimuth. A simple mount that moves the telescope up/down (altitude) and left/right (azimuth). Ideal for quick setup and tracking.

Aperture: The diameter of a telescope’s main lens or mirror. Larger apertures gather more light, improving image clarity—especially for faint deep-sky objects.

APO (Apochromatic): A type of lens design that reduces colour fringing (chromatic aberration), delivering sharper, more colour-accurate images.

B

Barlow Lens: A lens that increases the effective focal length of a telescope, magnifying the image without changing the telescope itself.

C

Chromatic Aberration: Colour fringing caused by lenses not focusing all wavelengths of light to the same point. Reduced in APO optics.

D

Deep-Sky Objects (DSOs): Distant objects like galaxies, nebulae, and star clusters beyond our Solar System.

Dobsonian: A type of reflector telescope mounted on a simple alt-azimuth base. Popular for its large aperture and low cost.

Dual-Band Filter: Enhances contrast in nebulae by isolating H-alpha and OIII emission lines, ideal in light-polluted skies.

Dew Heater: Prevents condensation on optical surfaces by gently warming the telescope lens or corrector plate.

E

EQ (Equatorial) Mount: A mount aligned with Earth's axis, allowing better tracking of stars and planets. Crucial for long-exposure astrophotography.

F

Focal Length: The distance from the lens or mirror to the focal point. Affects field of view and image scale—longer focal length means higher magnification.

Field Flattener: An optical element that corrects image distortion at the edge of wide-field images, commonly used with refractors.

H

H-alpha (Hydrogen Alpha): A red wavelength of light emitted by hydrogen gas, commonly observed in nebulae. Isolated by specialised filters.

I

Image Resolution: The amount of detail captured in an image, measured in pixels. Higher resolution means more visible structure in objects.

L

Light Pollution Filter: Blocks specific wavelengths from artificial lighting to enhance visibility of faint deep-sky targets in urban skies.

M

Mosaic: A feature that captures and stitches multiple images to create a larger, high-resolution field of view.

O

OIII (Oxygen-III): A teal-blue emission line from doubly ionised oxygen, often found in planetary nebulae. Isolated by narrowband filters.

OTA (Optical Tube Assembly): The telescope tube without mount or tripod—useful when building a custom setup.

P

Plate Solving: Software that identifies stars in a photo and compares them to a sky catalogue to determine exact pointing and align the telescope automatically.

R

RAW / FITS / TIFF / JPEG: Image formats used in astrophotography. RAW and FITS retain unprocessed data, TIFFs are high quality, and JPEGs are compressed for easy sharing.

Reflector: A telescope design using mirrors to gather and focus light. Well-suited for deep-sky observation.

Reducer: An accessory that shortens focal length to increase field of view and reduce exposure time.

Resolution: Image detail level. Higher resolution means more visible structure in deep-sky objects.

S

Stack / Stacking: Combining multiple short exposures into one to reduce noise and reveal faint objects.

Singularity: The app used to control Vaonis smart telescopes like Vespera. Offers alignment, imaging, and sharing tools.

T

Timelapse: A series of images or frames taken at intervals to show motion over time—e.g., stars moving across the sky.

Tracking: The telescope’s ability to follow an object’s movement across the sky, maintaining it in view or in the centre of an image frame.

Tripod Thread Size: 1/4" (standard camera mount, used by Dwarf 3) and 3/8" (heavier-duty, used by Vespera).