This quality control method makes lens debris easy to detect, and provides verification of lens cleaning effectiveness.

1. Lens Debris Detection
Using Contrast Enhancement
This quality control method makes solid and liquid
lens debris easy to detect, and provides verification of
lens cleaning effectiveness.
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2. Lens Debris Detection Using Contrast Enhancement
Requirements
• Digital camera and lens
• LCD monitor, preferably a large one for
more room to photograph
• Graphics program with a “layers” feature
and “levels” filter (examples shown here
use Photoshop)
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3. Lens Debris Detection Using Contrast Enhancement
Method Overview
1. Take multiple photographs of a flat, evenly lighted
surface (LCD monitor screen in this case)
2. Use a graphics program to create a file with each
photograph on its own “layer”
3. Increase contrast for each photograph using a “levels”
filter
4. Show and hide layers to confirm debris permanence
5. Note confirmed solid/liquid debris location
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4. Lens Debris Detection Using Contrast Enhancement
Stage 1: Photograph evenly lighted surface
• Using a graphics program, make an empty image
with the LCD screen's dimensions and fill it with
white. Show the white image full screen. Increase
the LCD monitor brightness for a lighter image.
• Take multiple camera photographs of the screen
with aperture priority mode, aperture at f/16, and
a low ISO. Set white balance as needed. Move the
camera while pressing the camera shutter to blur
the background and reduce any screen pixel
detail. This insures any focused objects are only
from the camera and lens.
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5. Lens Debris Detection Using Contrast Enhancement
Stage 2: Set up Layers in Graphics Program
• Transfer the camera photos to a computer. Open
the photos taken in a graphics program capable of
showing “layers” and having a “levels” filter. Place
each photo in a single document, with each photo
on its own layer. Name each layer according to the
photo’s filename.
Example using Photoshop:
Here three images are on their own
separate layer in one document. Hold
down the shift key while dragging-and-
dropping one photo on to another to
place it on its own layer and align it
with the current photo.
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6. Lens Debris Detection Using Contrast Enhancement
Stage 3: Apply Levels Filter
• Make solid/liquid debris easily visible by clicking on
each photo layer and applying a levels filter to
increase the contrast. Use the “auto“ levels button to
do this quickly.
Before applying levels filter to a photo Use Photoshop’s levels filter After applying levels filter to a photo
layer in Photoshop (Image menu > Adjustments > layer. Debris is now easily seen (shown
Levels...), click the “Auto” with arrows here.)
button, then click “OK” button.
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7. Lens Debris Detection Using Contrast Enhancement
Stage 4: Verify Debris Location Permanence
• Hide all photo layers except for the bottom layer.
Now repeatedly show and hide other layers.
Temporary aberrations will “blink” as layers are
shown and hidden. Anything which remains is debris.
Zoom to 100% and examine suspect areas as needed.
In Photoshop’s Layers palette,
clicking an eye icon will hide
or show that layer.
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8. Lens Debris Detection Using Contrast Enhancement
Stage 5: Note Confirmed Debris Location
• If the graphics program supports it, the coordinates of
each debris location may be noted. Show the palette
which notes the cursor's coordinates in the graphics
file. Move the cursor atop a confirmed debris location
and note the cursor's coordinates. Do this for each
confirmed location. The coordinates may be used with
automated cleaning machinery to clear the location.
In Photoshop’s Info palette
(Window menu > Info), the X
and Y coordinates of the
mouse cursor are shown.
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9. Lens Debris Detection Using Contrast Enhancement
After Cleaning...
• Repeat stages 1 to 4 to verify the debris
has been removed. Continue to stage 5 if
the debris still remains.
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