Compact extended-DOF microscope through electrowetting lens

In optical microscopy, the intrinsic trade-off between resolution and depth of field (DOF) prevents the observation of 3D samples, limiting the observable thickness to some micrometers. The usual solution to this problem is to mechanically scan the object in depth. However, this slows down the process and can induce vibrations in soft samples. To overcome these drawbacks, we propose the use of an electrically tunable lens (ETL) based on electrowetting effect. Specifically, we propose an extended-DOF microscope set up in a very compact architecture in which full telecentricity is no longer achieved. On top of that, the axial scanning is carried out by the non-afocal coupling between two M12 lenses and the ETL. The main feature of the proposed extended-DOF microscope is that, despite its compactness, it can capture stacks of images with long depth range, constant magnification and a spatial resolution that equals that of the standard microscope and remains invariant along the depth range. We also show that the proposed idea can be implemented as an add-on attachable to any commercial microscope, which enables the use of all the microscope facilities.