Phase contrast optical components can be added to virtually any brightfield microscope, provided the specialized phase objectives conform to the tube length parameters, and the condenser will accept an annular phase ring of the correct size.

An amplitude specimen decreases the intensity (i.e. the amplitude) of the light. Phase specimens cause a phase shift of the light. Phase contrast microscopy is now capable of converting a difference in refractive index into a difference in brightness. …

Phase contrast condenser as seen on the microscope. Set the condenser on the BF setting and focus on a specimen. Adjust the height of the condenser for optimum image quality. Move the condenser turret to the phase setting for whichever lens you are currently using and remove the specimen.

The following steps are recommended for the alignment of a phase contrast microscope.

1. Place a brightly stained specimen on the stage and rotate the 10x phase contrast objective into the optical pathway in brightfield illumination mode.
2. Remove the stained specimen and place a phase specimen on the microscope stage.

To ensure proper phase ring/plate alignment, first toggle the Phase Telescope radio button to the In position and use the sliders to align the plate outline within the phase ring. Then toggle the Phase Telescope out of the light path to view the specimen under optimum conditions of phase contrast illumination.

To align, turn the brightness knob down to a fairly low setting, then remove the frosted glass filter from the light path. On an upright microscope place a piece of lens paper over the field diaphragm to see the image of the filament.

When imaging specimens in the optical microscope, differences in intensity and/or color create image contrast, which allows individual features and details of the specimen to become visible.

Phase-contrast microscopy is an optical microscopy technique that converts phase shifts in light passing through a transparent specimen to brightness changes in the image. Phase shifts themselves are invisible, but become visible when shown as brightness variations.

Disadvantages

• Annuli or rings limit the aperture to some extent, which decreases resolution.
• This method of observation is not ideal for thick organisms or particles.
• Thick specimens can appear distorted.
• Images may appear grey or green, if white or green lights are used, respectively, resulting in poor photomicrography.

Brightfield, darkfield, and phase contrast are the most common label-free contrast modes used in optical microscopy. Brightfield imaging is most suitable for observing samples with strong absorption. Darkfield imaging provides good contrast for subresolution features, since it only captures high-angle scattered light.

Phase, phase angle, or phase shift is the state of progresssion of a periodic system. The symbol for phase is φ (lowercase phi). The SI unit of phase is the radian [rad], but degrees may also be used (°). Phase can also be decribed as a fraction of a cycle or a period.

The phase difference is <= 90 degrees. It is customary to use the angle by which the voltage leads the current. This leads to a positive phase for inductive circuits since current lags the voltage in an inductive circuit. The phase is negative for a capacitive circuit since the current leads the voltage.