by way of Jeanne Anderson <[EMAIL PROTECTED]>
Wed, 6 Oct 1999 11:00:11 -0700
Dear Jim: Yes, the appropriate blur size to use is the pixel center-to-center spacing. Why this is correct: The size of the blur spot (which will be a circle when one has a circular pupil, and also be fairly uniform in intensity when one has an otherwise well-corrected system experiencing almost pure "defocus") should match the resolution of the sensor. The sensor may be film, the human retina, an electronic camera focal plane, etc. For an electronic imaging device, this resolution will be limited by the spacing from one pixel to the next, i.e., the pixel's center-to-center spacing. Thus, the rule-of-thumb you quoted is both logical and also works well in practice. (Please note that the pixel center-to-center spacing can be different in the vertical and horizontal directions. Check both!) As they say, a picture is worth a thousand words, so if you'd like, I will send you a diagram which shows just how this relationship between depth of focus, blur spot size, and pixel to pixel spacing works, just let me know. If I can be of any further assistance, please call me at 800-217-7920. Best Regards, Kevin --------------------------------------- Kevin Hines Complete Optical Solutions, Inc. Providing Optical Consulting, Design and Engineering Services Imaging, Fiber Optic & Laser Systems Toll-Free: 800-217-7920 Or: 540-977-2092 Fax: 540-977-5364 129 Stratford Drive Blue Ridge, VA 24064 USA [EMAIL PROTECTED] www.completeoptical.com --------------------------------------- In a message dated 10/4/99 10:23:13 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: > Subj: Depth of Field calculation for area arrays ... > Date: 10/4/99 10:23:13 AM Eastern Daylight Time > From: [EMAIL PROTECTED] (by way of Jeanne Anderson <[EMAIL PROTECTED]>) > Reply-to: <A HREF="mailto:[EMAIL PROTECTED]">[EMAIL PROTECTED]</A> > To: [EMAIL PROTECTED] > > > Dear Colleagues in the Electronic Imaging Technical Group: > > I have been trying to calculate depth of field for certain > close-up situations in my own work. I am quite familiar > with the standard formulae for determining the bounds of > the depth of field ... > > Near Limit : > > Dn = 1/(1 + Dcf/F**2) > > Far Limit : > > Dn = 1/(1 - Dcf/F**2) > > where > > D = focused distance, c = limiting circle of confusion, > f = f-number of the lens apertue, F = focal length of the lens. > > My question relates to the "appropriate" value to use for > the circle of confusion. Typically, for film, a value of 1/1000 > of the focal length of the lens is used (Focal Encycopedia of > Photography). Alternatively, an absolute value of 1/30 mm is > recommended (Kingslake, R. "Optical System Design"). However, > these figures are based on the limits of human vision when > examining FILM. (The basis for these values is ... "How big > can a point-image become before it is no longer perceived as > a point?") > > Clearly, video systems and CCD sensors introduce another element > to this. I've made a brief examination of the literature, and > the best discussion I can find is a technical note provided by EG&G > Reticon in their camera handbook (Application Note #127). In this > paper, the authors use the inter-pixel spacing as the "appropriate" > value for the circle of confusion ("acceptable blur spot"). Can > anyone on this list justify/dispute this for me? My intuition tells > me this is probably a good "starting point", but my intuition and > reality are often at odds with each other. The EG&G note simply > states what is done, without justification. It does not attribute > the note to a particular individual. > > Any thoughts, feedback, references, etc. would be helpful. > > Regards, and thanks, > > Jim WALTON > Chairman, SPIE Technical Group on High-Speed Photography, > Videography and Photonics > > ************************************************************* > ************************************************************* > * * > * 4D VIDEO CELEBRATED ITS 11TH ANNIVERSARY ON OCTOBER 1 '99 * > * * > ************************************************************* > ************************************************************* > * * * > * JAMES S. WALTON, Ph.D. * INTERNET: [EMAIL PROTECTED] * > * President, 4D VIDEO * * > * 825 Gravenstein Hwy North * PHONE: (707) 829-8883 * > * Suite #4 * * > * SEBASTOPOL, CA 95472 * FAX: (707) 829-3527 * > * * * > ************************************************************* > ************************************************************* >