Example of Depth of Field characteristics for CCD vs CIS Sensors.

 

The CCD (Charged Coupled Device) sensor as used in a large number of Flatbed scanners has far better Depth of Field than a CIS (Contact Image Sensor).

This is a very simple test of a scanners depth of field (distance in focus above the glass).  Both images were scanned in color at 200 DPI. The images were then reduced for the web.

Click on image for the full size image (2200 X 333 pixels)

CCD_8400F_Raised_2inch.jpg

The Image above is made with a Canon Canoscan 8400F scanner, The 12 inch ruler is raised 2 inches on one end, the other end is touching the scanners platen (Glass). The Canon 8400F has a CCD for its imaging sensor. You will notice that the bottom of the wood block is in sharp focus while the ruler above the block is out of focus.

Click on image for full size image (2428 X 395 pixels)

CIS_Sensor_ScanExpress_A3_USB.jpg

The Image above is made with a Mustek Scan Express A3 scanner, The 12 inch ruler is raised 2 inches on one end, the other end is touching the scanners platen (Glass). The Mustek ScanExpress A3 scanner uses a CIS sensor. You will notice that the bottom of the wood block is in sharp focus while the ruler above the block is out of focus.

When I did the scan, I thought WOW, that sensor really has no DOF. I have been saying all along that the CIS sensor had no Depth of Field.
When I did the first scan, I first thought I did something really wrong. It is in focus for a very short distance from the glass.
If you look close at the CIS image, the first about 1 maybe 2 CM is usable. About 3/4 inch on the inch scale.

By contrast, the CCD image is almost usable the whole length of the ruler. It starts getting fuzzy about mid way, around 6 inches. At that point the ruler is about 1 inch above the glass.


It is plain to me that a CCD sensor is a far better sensor for a scanner, even the lower end of the ruler is in shaper focus on the scanner with a CCD sensor.

Click on small image for a larger image.

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Picture of the ruler and 2 inch block on the glass of the Canon Canoscan 8400F scanner.

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Picture of the ruler and 2 inch block on the glass of the Mustek ScanExpress A3 scanner.

 

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Copyright Carl McMillan 2007.

Page last edited: March 23, 2009