Results 1 to 1 of 1
  1. #1
    admin's Avatar
    admin is offline Administrator
    Points: 6,989,798, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Overall activity: 5.0%
    Achievements:
    First 1000 Experience PointsGot three Friends20+ Friends Achievement!5+ Referrals Achievement!100+ Threads Achievement!
    Join Date
    Mar 2007
    Location
    Sydney, Australia
    Posts
    13,468
    Points
    6,989,798
    Level
    100
    Thanks
    18,563
    Thanked 7,912x 3,807 Posts
    Blog Entries
    2

    Default Telescope Optical Quality Analysis Strehl Ratio



    I didn't know about this ratio until quite recently


    The Strehl ratio, named after the German physicist and mathematician Karl Strehl (1864-1940), is a measure for the optical quality of telescopes and other imaging instruments. It is defined as the ratio of the observed peak intensity at the detection plane from a point source compared to the theoretical maximum peak intensity of a perfect imaging system working at the diffraction limit. This is closely related to the sharpness criteria for optics defined by Karl Strehl.[1][2]

    Unless stated otherwise, the Strehl ratio is usually defined at the best focus of the imaging system under study. The intensity distribution in the image plane of a point source is generally called the point spread function. Obviously, characterising the form of the point-spread function by a single number, as the Strehl Ratio does, will only be meaningful and sensible if the point-spread function is little distorted from its ideal (aberration-free) form. This is valid for well corrected systems that operate close to the diffraction limit. This includes most telescopes and microscopes, but excludes most photographic systems, for example. The Strehl ratio has been linked via the work of Marechal to an aberration tolerancing theory which is very useful to designers of well corrected optical systems, allowing a meaningful link between the aberrations of geometrical optics and the diffraction theory of physical optics. A significant shortcoming of the Strehl ratio as a method of image assessment is that, although it is relatively easy to calculate for an optical design prescription on paper, it is normally difficult to measure for a real optical system, not least because the theoretical maximum peak intensity is not readily available.

    The ratio is commonly used to assess the quality of seeing in the presence of atmospheric turbulence and assess the performance of any adaptive optical correction system. It is also used for the selection of short exposure images in the lucky imaging method.

    In industry the Strehl ratio has become a popular way to summarize the performance of an optical design because it gives the performance of a real system, of finite cost and complexity, in terms of a theoretically perfect system which would be infinitely expensive and complex to build and would still have a finite point spread function. Essentially, it's the square of the ratio of the point spread function you've got to the best point spread function money can buy.

    It provides a simple method to compare a system with a Strehl ratio of, for example 0.95 is good enough, or whether twice as much should be spent to try to get a Strehl ratio of perhaps 0.97 or 0.98.
    Note the measurement of the ratio varies depending on the measuring instrument used, light used, colour and more.

    Some similarly measured Strehl values:

    Scope Name - Stehl Ratio (1.0 is best)


    SkyWatcher
    ED100 - 0.98
    ED80 - 0.975

    William Optics
    Wo 66sd - 0.97
    Name: Gus OTAs: ED 100 PRO refractor, Orion ST80 (not the CF), 8" Dob stuck in Canada Mounts:HEQ5PRO Synscan mount, Manfrotto Tripod CAMS: Guidecam Philips SPC900 webcams (4), Canon unmodded-450D DSLR

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.


    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    |
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    | My Astronomy Blog

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.


  2. The Following 4 Users Say Thank You to admin For This Useful Post:

    andyp180 (01-28-2011),ibase (01-28-2011),OleCuss (07-01-2011),rohitud (09-06-2012)

 

 

Similar Threads

  1. Telescope Optical Mirror Quality Make Big Difference?
    By Bruce M in forum Telescope Forum
    Replies: 0
    Last Post: 08-30-2008, 01:25 PM
  2. Optical Quality of the Eye
    By Alan French in forum Amateur Astronomy Forum
    Replies: 50
    Last Post: 12-13-2004, 12:40 AM
  3. strehl ratio for obstructed scopes
    By Mark Squicquero in forum Amateur Astronomy Forum
    Replies: 41
    Last Post: 10-16-2004, 01:20 PM
  4. strehl ratio
    By Jan van Gastel in forum Amateur Astronomy Forum
    Replies: 13
    Last Post: 06-15-2004, 11:59 PM
  5. Strehl Ratio
    By Evan Miller in forum Amateur Astronomy Forum
    Replies: 2
    Last Post: 04-18-2004, 05:32 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Powered by vBulletin® Version 4.2.0
Powered by vBulletin®
All times are GMT. The time now is 01:36 AM.