Re: Depth of Focus Formula
From: W. Watson (wolf_tracks_at_invalid.inv)
Date: 02/25/05
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Date: Fri, 25 Feb 2005 15:49:38 GMT
JK (at mail dot dk) wrote:
> On Thu, 24 Feb 2005 03:11:56 GMT, "W. Watson"
> <wolf_tracks@invalid.inv> wrote:
>
>
>>I'm looking at a formula for depth of focus on a web site, and it shows equation
>>depth->subscript of(diffraction) is equal to the 1.22*wavelength divided by the
>>sine squared of a half angle (Where the sine argumentis the half angle subtended
>>by the lens as seen from either the object or image plane). Anyone know where
>>the formula came from? Perhaps someone of historic merit derived it? Where can I
>>find a description or reference to it?
>
>
> I don't remember exactly why it was derived so. But you must know that
> diffraction formula and depth of focus are related.
> I mean the formula for diffraction limited resolution.
>
> Certainly we know that when we stop down the aperture in a lens the
> depth of focus increases. Stop 8 - 11 gives large depth and stop 2.8
> gives small depth.
>
> So:
>
> big aperture --> high resolution (when diffraction limited) and low
> depth of focus
>
> small aperture --> lower resolution but larger depth of focus.
>
> It is also logical from a ray-tracing point of view, that when rays
> comes to the image plane from a larger cone angle the focus will be
> well defined over a shorter distance only.
>
> Look in Born & Wolf or Jenkins & White to put some optics bibles
> loosely.
>
> best regards
>
> John
>
Unfortunately, I do not have access to those books. If you could scan a relevant
page from one, and send it to me at sierra_mtnview A-T earthlink.net that would
be appreciated. The only advanced book on optics I have is by Hecht. Maybe I
should invest in Bor and Wolf as another reference. I'll look on Amazon or
Powell. I hope optics is in the title.
--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet
Do you need 204,300 calories a day? A humming bird weighing
170 pounds would. Scientific note on a rufus's social behavior: None
Web Page: <home.earthlink.net/~mtnviews>
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