THE CONTRIBUTIONS OF OUT-OF-PLANE MATERIAL TO A SCANNED-BEAM LAMINOGRAPHY IMAGE

We studied the edge of a thin step wedge with a scanned-beam laminogra phy system to learn how material above and below the plane of focus co ntributes to the image. The edge of a planar, 0.5 mm (0.02 in.) thick lead sheet with large x and y dimensions was centered in the field of view. Images were captured as the lead sheet was moved in 0.075 mm (0. 003 in.) steps above and below the plane of focus of the system. The b lurring (measured as its width on the image) was no more than 0.1 mm ( 0.004 in., or the system resolution) when the sheet was in focus and i ncreased linearly with the deviation from focus. Blurring of out-of-pl ane objects is an essential feature of this laminography system, and i s used to minimize the contribution to the image from material above a nd below the plane of focus. The gray-level intensity in the blur chan ged approximately linearly over its entire width (linear change from d ark to light). We also imaged various three-dimensional structures to show the ability of laminography to resolve different planes of focus.