As a matter of performance, lenses often do not perform optimally when fully opened, and thus generally have better sharpness when stopped down some note that this is sharpness in the plane of critical focus, setting aside issues of depth of field.
32.
The diaphragm of these lenses remained fully open, providing a bright viewfinder image, until the button was depressed halfway, when the iris would be stopped down to the shooting aperture; pressed farther, the lens button engaged the camera's shutter release button, tripping the shutter.
33.
"It was a crime against all humanity and it should be eradicated and stopped down as a plague, " said Everit's colleague, Staff Sergeant Douglas Oakly, 36, of Billings, Montana, who also fought Saddam Hussein's forces in the Iraqi desert.
34.
:: : : Science fiction writer Arthur C . Clarke noted the relative brightness of the starts versus the lunar surface and the absence of stars when the lens is stopped down for correct exposure of the bright lunar surface long before the first lunar landing, so I was aware of that notion before the landing, and I assume NASA was too.
35.
Since the only possible metering is through-the-lens, the lens must be manually stopped down to accurately meter at anything less than full aperture . ( This is called stop-down metering . ) With the introduction of the Canon EOS-M mirror-less digital camera, an inexpensive adapter allows the full use, including infinity focusing, of nearly all FD and FL lenses.
36.
In Autogain framing live view, such as in AE modes with Auto ISO in effect, using the dof button can take on two different effects : autogain during aperture stopped down ( easy to see dof preview ), and autogain-locked or suspended during aperture stopped down ( difficult to see dof, just like looking with a non-live view DSLR of optical viewfinder ( OVF ) preview through-the-lens ( TTL ).
37.
In Autogain framing live view, such as in AE modes with Auto ISO in effect, using the dof button can take on two different effects : autogain during aperture stopped down ( easy to see dof preview ), and autogain-locked or suspended during aperture stopped down ( difficult to see dof, just like looking with a non-live view DSLR of optical viewfinder ( OVF ) preview through-the-lens ( TTL ).
38.
In truth, the reason there were no obvious stars in the photos ( actually, you can see some ) was because the brighter objects in the foreground ( the astronauts, lander and lunar surface ) were being lit by EXTREMELY bright sunlight ( brighter than on earth because of no atmosphere )-and the camera's lens had to be stopped down to prevent it from over-exposing the film and washing out the whole image to a white blur.
39.
If you have an f / 2 lens, say, that means the diameter is 1 / 2 the focal length, and it will gather twice as much light as an f / 2.8 lens, 4 times as much as an f / 4 lens-- remember that the area varies as the square as the diameter . ( In brighter light you don't need the full diameter of the lens, so the lens may be " stopped down " to f / 8 or or f / 16 or whatever in order to improve the depth of field.
