Question

Is there a way to check to see if there is dirt or debris on the image sensor that is causing image problems?

Answer

Yes, there is. You can review the flat-field correction image for the camera in question.

The flat-field correction image is used to flatten an image due to light gradients in the illuminator, objective, or image sensor and to level out minute variations in the sensitivity of adjacent pixels on the image sensor. The flat-field image is captured in air and should be completely free of image debris or other effects caused by the slide.

It is rare, yet possible, for parts of the uScope light path to become dirty. The light path includes the following possible sources of obstruction:

• Dirt or Debris on the Nose of the Objective
  This is possible if you scan or browse thick samples with no cover slip and the objective comes in contact with the specimen. Typically, a dirty objective causes the image to be blurry without good focus.
• Dirt or Debris on the Back Side of the Objective
  This is very unlikely. Typically, this causes blurry spots that cannot be focused. These spots are transparent and are not always problematic.
• Dirt or Debris on the Mirror
  This is possible but very unlikely.
• Dirt or Debris on the Relay Lens (uScopeHXII only)
  This is possible but it is unlikely to cause much of a problem.
• Dirt or Debris on the Image Sensor
  This is possible but unlikely. Typically, dirt or debris on the image sensor is opaque and has a very hard, distinct edge. If it is determined that the image sensor has become dirty, you must return the unit to your local distributor for cleaning.

Any contamination in the light path will be captured by the flat-field image which you can review.

The following flat-field images illustrate various light path effects.

Typical Flat-Field Image

This is a typical flat-field image for a uScope. There are no discernible light or dark spots on the image. The lighting is consistent with some possible vignetting at the corners (which is expected).

Note
If your flat-field image looks anything like this, it is good. There is nothing in the light path or on the image sensor to be concerned with.

Flat-Field Image Showing Small Debris

This flat-field image shows several dark spots. These are caused by very tiny debris (2-3 microns in size) on the image sensor.

These spots are not completely opaque and are not a cause for concern. You should not be able to detect these spots on images captured and filtered with flat-field correction.

Flat-Field Image Showing Water Spots

This flat-field image shows several light spots (and a few dark spots). The light spots are caused by water spots on the image sensor. They are caused when too much cleaning solution is used to clean the image sensor. Some of the spots may be difficult to see.

These spots are typically no cause for concern. You should not be able to detect them on images filtered with flat-field correction.