Welcome to Astronomy & Telescope Astronomy

 
 

  Modules

· Home
· AvantGo
· Content
· Downloads
· Encyclopedia
· FAQ
· Feedback
· Forums
· Journal
· Members List
· Private Messages
· Recommend Us
· Reviews
· Search
· Statistics
· Stories Archive
· Submit News
· Surveys
· Top 10
· Topics
· Web Links
· Your Account
 

  Who's Online

There are currently, 7 guest(s) and 0 member(s) that are online.

You are Anonymous user. You can register for free by clicking here
 

  Search



 

  Languages

Select Interface Language:

 

  Random Headlines


Natural Skylight
[ Natural Skylight ]

·Astronomy: Natural Skylight - THE ZODIACAL LIGHT
·Astronomy: Natural Skylight - AN ELUSIVE LIGHT
·Astronomy: Natural Skylight - CURTAINS OF LIGHT
·Astronomy: Natural Skylight
 

 
  Telescope Type: Astronomy: Telescope Type - SCOPE SPEED
Posted on Saturday, December 11 @ 01:08:36 CST by astronomy
 
 
  Telescope Type

SCOPE SPEED

A specification usually marked on the telescope's tube or given in its instruction manual is the focal length, almost always given in millimeters. This is the length of the light path from the lens or mirror to the focus point. With refractors and reflectors, the focal length is roughly equal to the physical length of the tube.

But in Maksutovs and Schmidt-Cassegrains, the light path is folded back and forth several times, allowing long focal-length optics to reside in a shorter, more compact tube.

Dividing the focal length of a telescope by its aperture in millimeters gives its ratio. A telescope with a focal length of 2,000 mm and an aperture of 200 mm (or 8 inches) is an f/10 telescope. If the focal length were 1,000 mm, it would be an f/5 scope.

The smaller the f-ratio, the faster the telescope. Fast telescopes are an advantage for deep-sky photography— an f/5 telescope will record a nebula in a quarter of the exposure time required by an f/10 telescope. Hence, the term "fast" telescope. For visual use, however, there is little advantage of one f-ratio over another. Slower telescopes are sometimes sharper, making them better suited to high-power planetary viewing, but they often have longer, less portable tubes. Fast telescopes give lower powers and wider fields with any given eyepiece, making them better suited to deep-sky viewing, but they also tend to exaggerate flaws in the optics.

There is no single ideal telescope, but by taking into account your skywatching interests, you can certainly make an informed choice.

 
 
  Login

Nickname

Password

Don't have an account yet? You can create one. As a registered user you have some advantages like theme manager, comments configuration and post comments with your name.
 

  Related Links

· More about Telescope Type
· News by astronomy


Most read story about Telescope Type:
Astronomy: Telescope Type - SCOPE SPEED

 

  Article Rating

Average Score: 0
Votes: 0

Please take a second and vote for this article:

Excellent
Very Good
Good
Regular
Bad

 

  Options


 Printer Friendly Printer Friendly

 Send to a Friend Send to a Friend

 

 
 
Associated Topics

Telescope Type
 
 


 
 
"Login" | Login/Create an Account | 0 comments
The comments are owned by the poster. We aren't responsible for their content.
 
 


 
 
No Comments Allowed for Anonymous, please register
 
 


 
  Astronomy & Telescope Astronomy

All logos and trademarks in this site are property of their respective owner. The comments are property of their posters, all the rest © 2004 by Astronomy & Telescope Astronomy
You can syndicate our news using the file backend.php or ultramode.txt