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Fixed focus lens / zoom
Two significant differences in lens appearance
Fixed focus lens only focus ring (that is, control definition)
The zoom lens has two rings, a focus ring (control definition) and the zoom ring (control perspective, the push-pull).
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[Use]
Using a zoom lens for focusing, it is best to consider first the image transferred to the maximum focus
In other words, the longest focal length lens-side focus.
Then, then the focal length to the desired focal length when shooting.
In this process, all focal lengths on the image is always clear.
(2) the use of this technology, because it is focused in the largest possible image, so can more easily observed in the image detail is clear, therefore the most accurate focus.
Some zoom need to turn to two separate control loops
A ring control of focus, and another ring to control the focal length.
The layout has the advantage of this structure is that once completed focus will not adjust the focus and accidentally changed the focus.
Four other zoom lenses only need to move a control ring, turn it focus, slide back and forth to change the focal length.
This "single ring" zoom lens for operation in terms of faster and more convenient, but usually more expensive.
Note, to change the focal length, do not lose the sharp focus.
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[Adjustment]
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Back focus
Focal length lens to the camera or zoom the image clarity with the need to adjust the focal length change.
Adjustment method is as follows:
1. A shot with different details of the image (preferably a dedicated test card), the object distance of 3 m to 5 m, adjust the aperture to the proper position, so to get a clear image on the viewfinder.
2 focus ring at the longest focal length the image transferred to the best definition.
3 down after the holiday in the shortest focal length focal length ring, so that the best image clarity.
Adjust the back focus ring, the first locking screw loosen, and then can rotate the focus ring.
Repeat the previous two steps, until the focus accurately track the zoom sharpness of the image always remains the same, and then tighten the back focus ring screws.
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Magnification mirror
A zoom lens of focal length, continuous regulation is limited in scope
Such as the focal length of a 21 × 7.5 zoom lens can be from 7.5 mm (perspective) transformation to 157.5 mm (the longest available focal length), its zoom multiples of 21, if the magnification microscopy (EXT) to select The switch from × 1 gear change to × 2 file, the zoom is still 21, but the focal length range of change into a 2 × (7.5 - 157.5) = 15 mm to 315 mm.
The use of magnification mirror need to pay attention to the following questions:
Join magnification mirror, the relative aperture of the lens decreases, arriving like the surface of the luminous flux will be reduced to 1/4, therefore, the aperture need to increase two tranches.
2 should not be used in a darker light magnification mirror, otherwise the captured image will be dark.
(3) the use of magnification mirror, capture an image perspective distortion and geometric distortion.
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Super close-up lens
Close-up distance of a variety of lens can not focus on objects within the close-up distance of 60 cm or more.
To be able to shoot the object close to the lens, the zoom lens in the rear of the lens are installed ultra close-up lens, marked with the word "MACRO".
The use of ultra-close-up lens as follows:
Filed or release (depending on the specific structure of an ultra close-up lens ring on the locking nail may be), turn the ring of super close-up to the white line in the direction of the MACRO word push to go, until it stops.
2 rotate the lens focusing ring to the closest distance.
(3) towards the subject, using the focus ring to adjust the clear shot.
(4) After the shooting, the ultra close-up ring and the locking nail to restore the original state.
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[King deep]
Whenever the lens for a subject adjusted the focus, all objects within the scope of the subject before and after a period is also clear.
Clear the scope of this focus is called depth of field, it is an important optical properties of the lens can be used as a tool of artistic creation.
When the main subject, together with all around the subject can focus clear space, he said the depth of field of the lens;
Around the main subject of this space, then the small depth of field of the lens.
(3) in terms of art or from the technical point of view, depth of field is very important.
From the artistic depth of field plays an important role in the perspective effect of the creative lenses;
Technically speaking, a large depth of field lens with the film is easier, if the depth of field is small, then with the camera or subject movement and constant focus.
Three elements --- the focal length / aperture / camera and the subject distance.
(1) the lens focal length is shorter the greater depth of field, depth of field decreases with increasing focal length.
(2) the smaller the lens aperture, the greater the depth of field.
(3) the greater the distance between the subject and the camera, the greater the depth of field.
In addition, the depth of field in the main photo objects behind the distance greater than the distance of the front
In other words, in the main the subject behind the subject in front of the clear focus range is greater than its range.
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【Article is excerpted from: Baidu Encyclopedia】
【Network reprint / Just reference】
【Translation is by Goolge】
