Reference Page
Telescope Specifications

F/ratio, Telescopes Specifications, Focal Length, Aperture

F/ratio of a telescope relates the focal length to the aperture. 
Specifically ratio = focal length / aperture.

F/10 would mean that the ratio, focal length / aperture = 10. 

So, a 10 inch telescope which is f/10 has a 100 inch focal length.  

It is best to consult the telescope manufacturer's specifications, as the f/ratios are rounded off.

When a telescope is focused, the focal length varies depending on temperature.

An astronomer may mask a  telescope's aperture for observations of bright objects such as planets or the moon.

A telescope's aperture may be blocked by the dome if it is not rotated with the movement of the telescope

Trees, buildings etc. might also block the telescope's view of the sky.

Telescopes Used in Optical Powers Module

Most of the images taken for the Optical Powers Module were taken with the following telescope systems:

The University of Chicago Yerkes Observatory Telescopes
40 inch f/19 refractor, conventional doublet lens, manufactured and designed by Clarks Brothers.
    The doublet is corrected for visible (yellow) light.
40 inch Warner & Swasey Ritchey-Chrétien reflector telescope.
    F/8 and f/13.5 secondary mirrors.
    Coude focus used for adaptive optics experiments.
    The coude feeds an optical bench located in the basement.
24 inch Boller & Chivens f/13.5 reflector.
     Rotatable main tube, useful for polarization measurements.
South Building Meade LX200 10 inch Schmidt-Cassegrain reflector
    F/6.3  Focal length = 1600 mm.  Diameter = 254 mm.

The University of Chicago Yerkes Rooftop Telescopes
South:  Meade LX200 8 inch Schmidt-Cassegrain reflector, f/6.3. 
    Focal length = 1280 mm.  Diameter = 203 mm.
North:  Meade LX200 10 inch Schmidt-Cassegrain reflector, f/10. 
    Focal length = 2500 mm.  Diameter = 254 mm. "ELM"
    Donated by Kevin McCarron in memory of his mother, science teacher, Eleanor L. McCarron.

Near and Far Sciences for Illinois (NFSI) Telescopes
Chicago: Meade LX200 7 inch Maksutov-Cassegrain reflector, f/15. 
    Focal length = 2670 mm.  Diameter = 178 mm.
Ken-Du-South: Meade LX200 8 inch Schmidt-Cassegrain reflector, f/6.3. 
    Focal length = 1280 mm.  Diameter = 203 mm.
Quincy: Meade LX200 10 inch Schmidt-Cassegrain reflector, f/6.3 
    Focal length = 1600 mm.  Diameter = 254 mm.

Telescopes Owned by Teachers
Meade LX200 8 inch Schmidt-Cassegrain reflector, f/6.3. 
    Focal length = 1280 mm.  Diameter = 203 mm.
    Owned by Kevin McCarron
Meade LX200 8 inch Schmidt-Cassegrain reflector, f/6.3. 
    Focal length = 1280 mm.  Diameter = 203 mm.
    Owned by Sharon Carr
Meade LX200 12 inch Schmidt-Cassegrain reflector, f/10 
    Focal length = 3048 mm.  Diameter = 305 mm.
    Owned by Frank Mills