Motic BA310E - Brightness and Contrast Adjustment

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4.9 Use of aperture diaphragm
 The condenser aperture diaphragm is provided for adjusting the numerical aperture (N.A.) of the
illuminating system of the microscope, it decides the resolution of the image, contrast, depth of
focus and brightness.
 Stopping down will lower the resolution and brightness but increase the contrast and depth of focus.
 An image with appropriate contrast can be obtained with an aperture setting that is 2/3 of the
objective N.A.
 To adjust the aperture diaphragm:
- adjust the condenser aperture diaphragm ring referring to the condenser aperture scale, or
- by observing the diaphragm image visible on the exit pupil inside the eyepiece tube, or
- by using a centering telescope after removing one of the eyepieces and focusing on the
aperture diaphragm.
4.10 Use of field diaphragm
 The field diaphragm determines the illuminated area on the specimen. For normal observation, the
diaphragm is set slightly larger than the field of view. If the illuminated area is set much larger than
the field of view extraneous light will enter the field of view. This will create a flare in the image and
lower the contrast.
 The thickness of the glass slide must be 1.7mm or less, otherwise the field diaphragm may not be
focused on the specimen plane.
 The diaphragm does not have any effect when the condenser top lens is swung out of the optical
path in the Swing-out type condenser. Fully open the field diaphragm, as the N.A. of the illuminating
system will be reduced if the diaphragm is excessively stopped down.
4.11 Brightness and contrast adjustment
 Neutral density filters are used for brightness adjustment in routine microscopy and
photomicrography.
 For phase contrast and contrast adjustment with black and white film, a Green interference filter
(546nm) is recommended.
 An HE (didymium) filter for colour photomicrography, Haematoxylin, Eosin (HE) or Fuchsin stained
specimen with tungsten type film is available.