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- Swing-Out Condenser
- It is not practical to use a single condenser with an entire range of objectives (4x-100x) due to the broad range of light cones that must be produced to match the numerical aperture of each objective. When using a lower power objective, such as 4x, the illumination cone will have a diameter of about 8mm, while the high power objectives (60x to 100x) need a highly focused cone measuring about 0.2-0.4mm in diameter. The numerical aperture determines the size of the cone of light. When the numerical aperture is bigger, the cone of light will be smaller.
- In order to fill the field of view with light, it may be necessary to remove the top lens of the condenser. Many manufacturers now produce a condenser which flips over completely called a swing-out condenser. These condensers work for objectives ranging from 4x-100x with numerical apertures ranging from 0.65 / 1.25 N.A. (for 40x – 100x) or 0.9 / 1.25N.A. (for 60x – 100x)
- When the objective is changed, for example from a 10x to 20x, the aperture diaphragm of the condenser must also be adjusted to provide a cone of light that matches the numerical aperture of the new objective. This is done by turning the aperture diaphragm control. There is usually a small index above the control with the exact indication of the adjustment that needs to be made for each objective.
- Condensers that have a numerical aperture value of 0.95 or less are intended for use with “dry” objectives. Flip top condensers that have a numerical aperture greater than 0.95 are intended for use with oil-immersion objectives and they must have a drop of oil placed between the bottom of the microscope slide and the condenser top lens when examining critical samples.
