Long working distance air objective for multiphoton microscopy

A microscope objective having a first proximal end and a second distal end, said distal end configured to be closer to a sample than said proximal end, said microscope objective comprising:

• a first stage comprising a diverging lens element having negative optical power such that collimated light incident on said diverging lens element is caused by said diverging lens element to diverge as said light propagates away from said diverging lens element in the direction of said distal end of said microscope objective;
• a second stage comprising a lens configured to receive said diverging beam and to cause the diverging beam to begin to converge from the widest lateral extent of the beam in the microscope objective or be collimated, said second stage more distal than said first stage;
• a third stage comprising multiple lens elements, said third stage more distal than said second stage such that said lens in said second stage is located between said diverging lens element in said first stage and said multiple lens elements in said third stage;
• and
• a fourth stage comprising a distal focusing lens having positive optical power to focus the beam down, said distal focusing lens being the lens that is closest to the focus of said microscope objective where said collimated light incident on the proximal end of said microscope objective will be focused, said fourth stage being more distal than said third stage such multiple lens elements in said third stage is between said lens in said second stage and said distal focusing lens in said fourth stage,
• wherein said microscope objective has a numerical aperture in the range from 0.55 to 0.65.