Re: Image sharpness and focus distance.

[SA Photographers <photo@xxxxxxxxxxxxxxxxxxx>]

>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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