Re: Image sharpness and focus distance.

[Robert Erickson <cirkut8@xxxxxxxxx>]

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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