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Article ID: NBR1245 — Created: 5 Apr 2019 — Reviewed: 19 Apr 2021
When I open the browser to review a specimen, the image is blurry. When I click the auto-focus button to automatically focus the objective the image gets better, but is still blurry. If I click auto-focus again, the image gets even better.
Is there something I can change to tune or improve the auto-focus operation?
Yes. There are several auto-focus parameters you can change to suit your needs. But first, a little information on how auto-focus works.
The auto-focus algorithm compares the contrast across the camera image to determine a "focus score". Each time the focus changes, a new focus score is calculated and compared to prior scores. The best score is the best focused image so far.
To limit the time spent trying to auto-focus, the range of focus adjustment is limited to a few hundred steps (a few dozen microns). This is a setting that you can adjust. The default setting was chosen in an attempt to strike a balance between speed and focus quality. You can increase the focus range if you want to search a wider range for focus.
Adjusting the Coarse Focus Range too high can cause the uScope to focus on debris, dust, fingerprints, etc. on the cover slip instead of the specimen. If the top of the coverslip is very dirty, the debris can create a very high contrast image that produces a high focus score which fools the focus algorithm.