A Barlow lens is a diverging lens which attaches to the objective lens on a stereo microscope. They are commonly used to alter a microscope's focal length, magnification power and field of view.
For example, a 0.5X Barlow lens will reduce the magnification by half and double the working distance and field of view. Similarly, a 2.0X Barlow will double the magnification and reduce field of view by half.
Different color light passes through curved glass (a lens) at different angles. Achromatic lenses 'correct' for this 'spherical aberration' in order to bring the light rays into focus on the same plane.
The better the lens, the greater is the amount of correction or 'flat field'. There are three common achromatic lenses:
Achromatic - Standard on most microscopes with 65% flat field .
Semi-Plan - Better quality with 80% flat field
Plan - Premium lenses with 95% flat field
Most applications only require standard achromatic lenses. Semi-plan and plan lenses are typically for professional use.
Please note that Semi Plan and Plan filters also include E-Plan, S-Plan and U-Plan objectives.
A high power or compound microscope achieves higher levels of magnification than a
stereo or low power microscope. It is used to view smaller specimens such as cell structures
which cannot be seen at lower levels of magnification.
A low power or stereo microscope typically employs objective lenses of 50x or less. It is used to view specimens that are visible to the naked eye such as insects, crystals, circuit boards and coins.
A stereo microscope has three key parts: