RE: Image sharpness and focus distance.

["M. Denis Hill" <denis@xxxxxxxxxxx>]

A reasonable definition is, "Acceptable Circle of Confusion is the size of
the largest circle which the eye cannot distinguish from a dot. In 35mm
format cameras, a 0.03mm diameter circle of confusion is considered
acceptable. It is used to calculate depth-of-field or depth of focus."
See a detailed discussion at http://artzonephoto.com/artzone/zlensthe.htm,
and more at http://www.minoxlab.com/Don_Krehbiel/mpl/dkdof.htm.

M. Denis Hill
Area 360 Communications
http://www.area360.com
360.678.8351

> -----Original Message-----
> From: SA Photographers [mailto:photo@xxxxxxxxxxxxxxxxxxx]
> Sent: Tuesday, October 24, 2000 11:22 AM
> To: panorama-l@xxxxxxxxxxxxxxxxx
> Subject: Re: Image sharpness and focus distance.
>
>
> From what little I can remember of my basic training in optics, the
> statement that only one plane can be sharp for a particular focus distance
> is correct but fortunately for us photographers, the human eye having the
> limitations it has, allows us to see unsharp images as sharp dependant on
> magnification, viewing distance and the acceptable circle of error. Which
> leads me to hyperfocal focussing points. I forget the formula but
> I am sure
> that enlightened members will supply it, but the upshot was that one could
> set the focus at a particular distance and all objects within the
> parameters
> appeared sharp. So for panoramas 4 meters to Infinity and an acceptable
> degree of sharpness would give an optimum hyperfocal distance.
> This formula
> could also be applied to near and middle distance subjects. The size of an
> object doesn't change with focus merely the degree of fuzziness and then I
> will throw in another bone of contention. Perspective is dependant on the
> point of view not the lens used i.e. all lenses have the same perspective
> when used from the same point of view only the angle of view changes.
>
> Craig Woods
> PO Box 91
> Honeydew 2040
> South Africa
> cwoods@xxxxxxxxxxx
> http://www.photographers.co.za/
> Mobile: 082-322-2851
> ----- Original Message -----
> From: "Robert Erickson" <cirkut8@xxxxxxxxx>
> To: <panorama-l@xxxxxxxxxxxxxxxxx>
> Sent: Tuesday, October 24, 2000 4:06 PM
> Subject: Re: Image sharpness and focus distance.
>
>
> > Take two individuals looking at the same image from a
> > Roundshot 24/35. One person will look at objects 20
> > feet from the camera and proclam the image sharp as a
> > tack. The other individual will look at objects on the
> > horizon and say that it is not as good as what they
> > would expect from their conventional 35mm camera. Both
> > are right!
> >
> > The question of sharpness for a revolving camera is
> > not as simple as what lens it uses. There is an other
> > factor to it. No fixed focus revolving camera can be
> > sharp at all distances. For any lens, when focused at
> > the horizon the image is a diferent size as it is when
> > focused at close distance. Most fixed focused
> > revolving cameras are pre set at the factory to be
> > focused AND to use that correct amount of film for
> > objects at about 20 feet or so. Objects in the close
> > forground and at the horizon will not only be out of
> > focus because of lack of depth of field but ALSO
> > because they are the wrong size for the amount of film
> > used. Even if you could set the lens a f/200 objects
> > in the forground and horizon can not be sharp because
> > they are the wrong size for the amount of film being
> > used. Adding a close up filter to a Roundshot 24/35
> > may improve the sharpness of an object close to the
> > lens, but it is physically impossiable to make it tack
> > sharp because the wrong amount of film is being used
> > for the size of the image.
> >
> > My circa 1905 Cirkut camera has gears to change the
> > amount if film used to match where the camera is
> > focused. The Super Roundshot has a computer to change
> > the amount of film pulled for where the lens is
> > focused. For my LarScan homebuilts I prefered to use
> > zoom lenses. I would shoot test rolls and mark on the
> > barrel where to set the zoom for different focus
> > distances and set the zoom for matching image size.
> >
> > Bob
> >
> >
> > =====
> > Robert Erickson, cirkut8@xxxxxxxxx
> > The Panoramic Network: http://www.panoramic.net
> >
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