Meade Instruments Infinity 80, 90 and 102mm Refractor User Manual

Page 14

HAVE A GOOD TIME,

ASTRONOMY IS FUN!

SPECIFICATIONS
Infinity 80 model:

Objective lens diameter 80mm(3.2”)

Optical tube focal length 400mm

Focal ratio f/5

Mounting type Alt-azimuth

Viewfinder Red-dot

Infinity 90 model:

Objective lens diameter 90mm(3.5”)

Optical tube focal length 600mm

Focal ratio f/6.7

Mounting type Alt-azimuth

Viewfinder Red-dot

Infinity 102 model:

Objective lens diameter 102mm(4.0”)

Optical tube focal length 600mm

Focal ratio f/5.9

Mounting type Alt-azimuth

Viewfinder Red-dot

What do the specifications mean?

Optical tube focal length is the distance light

travels in the telescope before being brought

to focus in you eyepiece. Depending on the

telescope model, the focal length is either

400mm or 600mm long. Look at the specifi-

cation table to find out your telescopes focal

length.
Objective lens diameter is how big the

front lens is on your scope. Telescopes are

always described by how large their objec-

tive lens is. Depending on your telescope

model, the lens diameter is either 80mm, 90

or 102mm.
Other telescopes are 50mm, 8 inches, 16

inches, or even 3 feet in diameter. The

Hubble Space Telescope’s objective lens

has a diameter of 2.4 meters (that’s 7.8 feet

across!).
The focal ratio helps determine how fast the

photographic speed of a telescope is. The

lower the focal ratio number, the faster the

exposure. f/5 is faster than f/10. The faster

the ratio, the shorter the exposure time is

needed when a camera is hooked up to the

telescope. For example, the Infinity 80 tele-

scope has fast focal ratio at f/5. Sometimes,

astronomers use focal reducers to make

slow exposure telescopes have faster focal

ratios.
Alt-azimuth mounting simply means your

telescope moves up and down (altitude

or “alt”), and side to side, (azimuth or “az”).

Other mounting configurations are available

for other telescopes, such as equatorial

mounting.

USE THE SPECIFICATIONS TO CALCU-

LATE THE MAGNIFICATION OF YOUR

EYEPIECE
The power of a telescope is how much it

magnifies objects. For an Infinity 90, the

26mm eyepiece magnifies an object 23.1

Looking at or near the

Sun will cause irreversible damage to your eye. Do not point this telescope at or near the Sun. Do not look through the telescope as it is moving.