The following image shows optical planes spaced 10 microns apart. Images show autofluorescence from a mouse brain imaged at 920 nm, starting from the very top of the sample (denoted as -30 microns). Here the field of view is large (about 1.6 mm) and the objective exhibits a good deal of field curvature so it takes 40 microns for the whole FOV to fill with sample. We would start imaging about 35 microns below the surface (about where is shown by 0 microns in this image series). Typically we aim for 40 micron sections, which means we'd acquire the images shown at 0, 10, 20, and 30 microns. The last 5 images look substantially fuzzier: the resolution is worse. For this reason we want to cut thin and start imaging as near to the surface as possible. A smaller FOV or an objective with a flatter field would allow us to start imaging higher up and so the whole stack would look better.