Question

Which focus method should I use when I scan my slides? Is there one that always gives the best results?

Answer

The uScope Navigator software offers several focus methods from which to choose. Each focus method is intended to solve a different problem when scanning various specimens. Unfortunately, there isn't just one focus method that works best for every situation.

Initial Focus Method

This focus method scans the region of interest using the same focus point for each field in the scanned area. This is the fastest focus method. It is useful for specimens (like insects or textiles) that are very thick.

Generally, when you scan extremely thick specimens with the initial focus the resulting deep zoom images look very good. If you scan thicker specimens with a focus method like Exhaustive Stack, the resulting fields do not combine well because each field is more likely to scan at a different focal plane and the edges (where the images overlap) are not focused the same.

Predictive Focus Method

This focus method automatically selects and captures exhaustively focused points (prediction points) from the region of interest. It uses the focal point of each of these prediction points to create a focus map that is applied to the remaining fields in the ROI. Since the focus points are pre-calculated, scanning is very fast.

If your region of interest is completely included in the interior of your specimen, this is probably the best focus method to choose. You can adjust the maximum number of fields between prediction points if your specimen is not particularly flat.

Note
You can adjust the distance between focus points in the device settings. Reducing the distance between points improves the focus algorithm's ability to detect very wavy specimens, but it slows down scanning.

Fast Stack Focus Method

This focus method is similar to the Initial Focus method. It captures a very short stack of images for each field (centered on the initial focus point) and chooses the one with the best focus. This focus method is best used for professionally prepared specimens that are very thin and flat. You can adjust the parameters for the image stack to best suit your specimen.

Scanning using this method is slower than the Predictive focus method but faster than the Exhaustive Stack method.

Note
You can set the range and step size for fast stacks in the device settings. Altering these settings may yield better results depending on the specimen and preparation.

Exhaustive Stack Focus Method

This focus method captures a deep stack of images for each field and chooses the one with the best focus. This focus method is best used when absolute best focus for each field is critical. It is the slowest focus method since it captures many images of each field in an effort to determine the best focus.

Note
You can adjust the range and step settings for various aspects of exhaustive focus stacks in the device settings.