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Location: UFOUpDatesList.Com > 2004 > Feb > Feb 29

Re: Whittlesea-Beveridge Photo - DeMary

From: Tom DeMary <t.demary.nul>
Date: Sun, 29 Feb 2004 01:32:59 -0600
Fwd Date: Sun, 29 Feb 2004 12:21:16 -0500
Subject: Re: Whittlesea-Beveridge Photo - DeMary


>From: Victor Golubic <Peetkin.nul>
>Date: Fri, 27 Feb 2004 18:54:14 EST
>Fwd Date: Sat, 28 Feb 2004 08:53:22 -0500
>Subject: Re: Whittlesea-Beveridge Photo - Golubic

<snip>

>If everyone will go to this web page you'll see that my
>calculation is very close, except that my assumption of
>the diagonal aperture of 6 mm is instead 6.44
>horizontal . . . which was the other explicitly stated
>alternative.

>http://www.imaging-resource.com/PRODS/DC240/240PICS.HTM

Sorry, I don't understand where 6.44 horizontal came from. I
think that is a number from your calculation below.

>Once your there, page down to the data on the macro
>shot of the dollar bill, it gives all the distance and width
>info from which you'll see that my assumption is quite
>close for 3.0x (others too). If it was 10 mm, then you just
>need to plug it in...I was only giving three reasonable
>points at 1, 2, and 3x.

>There you will read this, "With its zoom lens run out
>to the telephoto end of its range (3.0X), and the camera
>set for "macro" focusing, the DC240 does a very
>respectable job of close-up photography. The minimum
>focusing distance of 9.6 (9.5) inches (0.25 m) results
>in a reasonably "tight" minimum viewable area of
>2.6x3.4 inches (65 x 87 mm)."

This will not work properly, because the lens is altered by the
macro adjustment and focused at 9.5 inches, instead of infinity.
I don't think you can assume that the focal length is still 18mm
when the camera is macro mode.

>Calculating from this: 2 * Arctan ((3.4/2)/9.5) = 20.3
>degrees, one arrives at a value very close to what I
>provided for my 3.0X estimate of 18.9. However,
>this is the true horizontal dimension (confirmed here),
>Therefore, my assumption of the diagonally "film"
>aperture for the CCD being 6 mm is instead 6.44 mm
>horizontal.

OK, you are forcing your previous 18mm calculation to agree with
the FOV of the result from the test report by changing 6mm
diagonal to 6.44 horizontal. I think this is incorrect because
the focal length was no longer 3x. The lens was zoomed out to
3x, set to macro, and adjusted to minimum focus, which changes
the focal length of the lens.

<snipped calculations with 6.44mm sensor length>

After comparing the Kodak specs to a Sony DSC P30 camera,
pulling out hair, and web searching, I think that the Kodak
DC240 has a standard-sized "1/2.7" CCD chip. The active sensor
area has a 6.592mm diagonal, and is 5.270 x 3.960mm (4:3 ratio).
The horizontal FOV is 30 degrees at 10mm focal length.

>The web page I provided should help with many other camera
>manufacturers as well.

http://www.imaging-resource.com

is good. I like:

http://www.dpreview.com

too.

Tom DeMary




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