Automatic aperture control
In a single-lens reflex camera, I leave a diaphragm open at the time of the use of finder, and automatic aperture control (じどうしぼり) is mechanism to narrow down tie-dyeing to only at the time of exposure.
Table of contents
A single-lens reflex camera and diaphragm
As for the single-lens reflex camera, a lens for the photography can use the finder by putting a mirror from the end of the lens to a photosurface. For example, the photography using many interchangeable lens and telescopes, microscopes is in this way enabled. However, some problems that must be settled occur at the same time. One of those is the control of the diaphragm.
As a general rule, with the lens of the camera, it is necessary to narrow down a diaphragm at the time of the photography. However, if a diaphragm is not opening, a finder image is dark, and the depth of field is hard to focus it when I focus it in a finder because it is deep. In other words, I leave a diaphragm open at the time of the confirmation of the finder image and am preferable if I can squeeze it only at the time of photography. It is automatic aperture control to have realized this. The camera which realized complete automatic aperture control for the first time is ZUNO pentaflextime of the ZUNO optics industry.
Of course it is preferable to be able to narrow it down as needed to confirm depth of field in a finder. I call this function previews.
Control system of the diaphragm
I was how old, or the method to control a diaphragm has been devised in the past.
- Hand-operated diaphragm
- The camera does not control a diaphragm. The method that a diaphragm is narrowed down to immediately when I turn drawplate. A photographer leaves a diaphragm open by manual operation at the time of the use of the finder and photographs it afterwards after squeezing a diaphragm to an appropriate value. I usually say diaphragms.
- Diaphragm to pre-set
- The camera does not control a diaphragm. A ring and a narrowing ring setting diaphragm stop are distributed. It stops in a place narrowed down to diaphragm stop that I set beforehand when I operate a narrowing ring. For a hand-operated diaphragm, it is an advantage I narrow it down without taking the eyes off a finder, and to be able to operate.
- Half automatic aperture control
- A camera squeezes the diaphragm to the diaphragm stop that set beforehand automatically, but the return to opening lever operation roll up; such as the operation is hand-operated, and perform it.
- Complete automatic aperture control
- A camera squeezes it to the diaphragm stop that set a diaphragm beforehand automatically. The return is automatic, too, and the photographer does not need all operation other than setting of the diaphragm numerical value.
Interlocking movement method of the automatic aperture control
It is necessary to transmit a shutter release to the lens side by some kind of methods from the camera side so that a diaphragm is squeezed in conjunction with a shutter release by the automatic aperture control (including the half automatic aperture control).
- Release interlocking movement method
- The release button which a diaphragm is narrowed down to when I am pushed into a lens is on and functions like perfection automatic aperture control with a release button on the camera side all in one body when I attach it to a camera. It was adopted on the camera lenses of the exa- Kuta mount, but the limit of the lens diameter was big, and the structure became outdated to be complicated.
- Pin burglary method
- The method that a diaphragm is narrowed down to when an established pin is pushed into the lens mount inside with an interlocking device on the camera side. An example adopted in the dental plaque Chika mount (M42 mount) is famous. To AE which is given priority to a shutter speed because an operation stroke of the narrowing pin is short became outdated without being able to cope.
- Outside lever interlocking movement method
- A method to let you establish the narrowing interlocking movement lever in the lens outside and link a camera side lever. It was adopted in automatic Mecs or Toad Venom Rex of the Miranda camera. Because an interlocking movement lever exposed outside worked in a shutter release, I often woke up movement defectiveness in the way of the photographer and was hardly used.
- Internal lever interlocking movement method
- It is a method to let you put an interlocking movement lever in the mount inside by the most common method and link a shutter release. There were a regular opening type and regular narrowing type, but I always narrowed down many makers, and the regular opening type adopted a model because mechanism to change to a manual operation diaphragm for the case that I used a bellows device or a reverse ring for was necessary. Only a limited maker including Canon adopts the regular opening type.
- Electronic control interlocking movement type
- A method to open and close a wing with a solenoid or a stepping motor on the lens side, and to perform the control by an electrical signal. It is adopted in the Canon EF mounts. Because a mechanical interlocking movement with the lens side is not necessary, it is easy to put automatic aperture control mechanism on the special lens including the shift lens, but causes the movement defectiveness when the point of contact becomes dirty.
Fault of the automatic aperture control
There is not it without squeezing it like a hand-operated diaphragm because it is necessary to be able to open and close a diaphragm instantly, and the automatic aperture control increasing the number of sheets of the feather, and doing it with the diaphragm that a perfect circle is near. The limit of the number of diaphragm feathers is nine pieces by the automatic aperture control basically. When it increases the number of feathers further, this is because it cannot smoothen the opening and shutting of the diaphragm. Therefore the diaphragm shape that senility in particular was circular in the neighborhood of opening to grow big, and even a diaphragm feather of little number of sheets was near and the diaphragm feather which I devised so that it was came to be developed.
Allied item
This article is taken from the Japanese Wikipedia Automatic aperture control
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