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  1. Path: sparky!uunet!das.wang.com!ulowell!news.bbn.com!noc.near.net!hri.com!spool.mu.edu!howland.reston.ans.net!usc!rpi!utcsri!torn!watserv2.uwaterloo.ca!watmath!accwai
  2. From: accwai@math.uwaterloo.ca (Andy Wai)
  3. Newsgroups: rec.photo
  4. Subject: Re: Which 210mm 5.6 copal ?
  5. Message-ID: <C1IH72.M77@math.uwaterloo.ca>
  6. Date: 27 Jan 93 11:57:02 GMT
  7. References: <1993Jan26.113727.9273@spectrum.xerox.com> <C1GvE3.H0D@math.uwaterloo.ca> <1k451eINNquf@fnnews.fnal.gov>
  8. Distribution: na
  9. Organization: Math Faculty Computing Facility, University of Waterloo
  10. Lines: 24
  11.  
  12. In article <1k451eINNquf@fnnews.fnal.gov> nicinski@fndaud.fnal.gov (Tom Nicinski) writes:
  13. >In article <C1GvE3.H0D@math.uwaterloo.ca>, accwai@math.uwaterloo.ca (Andy Wai) writes:
  14. >
  15. >                                                        (mm)        (deg)
  16. >Lens                      Length Apert Coverage@f/22 Shift Rise  Swing Tilt
  17. >------------------------- ------ ----- ------------- ----- ----- ----- -----
  18. >Sinaron-S                  210mm f/5.6  310mm  72deg  82.9  90.5  18.0  20.3
  19. >Schneider APO-Symmar       210mm f/5.6  305mm  71deg  80.2  87.8  17.5  19.8
  20. >Nikkor-W                   210mm f/5.6  295mm  70deg  74.9  82.3  16.5  18.7
  21. >
  22. >|> If angular coverage are the same, how can image circle be different?
  23. >
  24. >The angle of coverage is only an approximation.  Use the image circle to get the
  25. >actual angle of coverage (72.86 vs. 71.97 vs. 70.17 degrees).
  26.  
  27. Actually they're both approximations.  The "image circle" that got thrown
  28. around all the time is actually the circle of good definition.  The image
  29. doesn't drop off abruptly at the edge of the published circle.  It softens
  30. up and falls off gradually.  The exact published circle size therefore
  31. depends heavily on what each manufacturer mean by good definition, which
  32. is quite arbitrary in my experience.  So a degree or two usually mean very
  33. little in practical terms.
  34.  
  35. Andy Wai
  36.