aperture diaphragm

ap·er·ture di·a·phragm

a metal device that limits the area of the beam emerging from an x-ray tube.
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One important point to remember when using an external aperture mask is to make sure the camera's internal aperture diaphragm is open all the way; otherwise, the blades will still introduce diffraction spikes in the optical path even when you've put on the circular mask.
The study yields the following results: the radiologic technologists in Cagayan de Oro City and Bukidnon highly practiced radiation protection particularly the use of the aperture diaphragm and avoidance of repeat examination.
The substage condenser must have a continuously variable circular aperture diaphragm (A stop) and be capable of true Kohler illumination for the full spectral range of 350 to 950 nm.
It also has minimum focal distance at 5 centimeters and the latest 9-blade aperture diaphragm that achieves a soft background blur effect.
There's also an 11-blade aperture diaphragm, which provides soft background blur when a subject is isolated from its background.
Distortion is small in lenses with constructions symmetrically configured on both sides of the aperture diaphragm, but is likely to occur in lenses having asymmetrical configurations.
Advanced microscopy systems automatically store the field and aperture diaphragm and the light intensity settings for each combination of magnification and contrasting methods.
Remove the eyepiece and close the aperture diaphragm by 1/3
The aperture diaphragm on the microscope can be used to control NA also, fine-tuning the balance between resolving power and depth of field.
The lens features a nine-blade curved aperture diaphragm to provide beautiful, blurred backgrounds even at full-zoom range.
Seven-blade aperture diaphragm that helps to create smooth and round bokeh effects.