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[Concept] Fixed focus lens (prime lens) refers specifically to only a fixed focal length lens, only one focal length, or only one field of view. ======================== [Sub class] ----------- (1) In accordance with [focal length] Fixed focal length / telescoping / Auto Iris / Manual Iris ----------- (2) in accordance with the focal length figures] Standard lens, wide-angle lens, the telescope top type. ----------- (3) In accordance with [aperture] Fixed-aperture (fixed iris) / Manual aperture (manual the Iris) / Auto aperture (auto iris) ----------- (4) in accordance with the telescopic lens adjustment method Automatic zoom lens / manual zoom lens ======================== [Excellent point] Mainly reflected in the use of short focal length ----------- A fixed focal length wide-angle or standard lens than the general covers a large diameter of the appropriate focal length zoom lens. Fixed focus wide-angle lens aperture is 2.8 or above, the light through a large amount of easy shooting in low-light situations. ----------- 2, the fixed focus wide-angle lens than the general cover the corresponding focal length zoom lens focusing distance of nearly. Such as the EF17-35 Closest focusing distance 0.42m and EF20/2.8, EF24/1.4, EF28/1.8, EF35 / 2 of the closest focusing distance are 0.25m. Closest focusing distance many advantages, especially for wide-angle lens, the focusing distance of nearly means being able to very close to approaching the subject, get a large knot like. And their large aperture with zoom wide-angle lens is not easy to achieve wide-angle bokeh effect. ----------- 3, the fixed focus wide-angle lens general than covered by the appropriate focal length zoom lens, small size, light weight. This enables your camera will not be so loud, easy to capture. ----------- 4, wide-angle fixed focus lens is generally better than zoom wide-angle imaging is good, which is determined by the design of the lens, the zoom lens to consider all focal length of the segment has a relatively good imaging, it is necessary at the expense of local interests to overall a relatively good performance. Fixed focus lenses do not consider these. ======================== [Disadvantages] Fixed focus lens only drawback I am afraid that is not convenient, the need to adjust the size of the object shooting only through the photographer's mobile capability in some occasions not suitable for mobile. ======================== [Select reason] ------------------ Fixed focus lens, of course, started as the first choice of 50. The classical three-mirror combination is like this: 35,50,135, with three lenses, be able to meet most occasions. If necessary in the future, further expansion. ------------------ In addition to providing a few different combinations for your reference. People love to shoot landscape can be considered three-mirror combination for 24,35 ﹝ 35 instead of 50 ﹞, 135. Love to shoot portraits of people: 35,85 ﹝ with 85 on behalf of 50 ﹞, 180. ------------------ An affordable price] In general, the price of the fixed focus lens than the zoom lens is more affordable, relative zoom lens, a PrimeLen fewer lens group and a more simple structure, in general, the best fixed focus lens only zoom the half the price, the 50mm focal length is almost the cheapest various lens focal lengths. ------------------ (2) a smaller distortion] Distortion zoom biggest weakness, and almost all wide-angle zoom lens distortion, fixed focus lens, just to correct and optimize the imaging of a focal length, so there is often little there will be distortion phenomenon. Also worth mentioning is that the rangefinder camera in the wide-angle distortion than SLR cameras have a natural advantage, such as 15mm/f4.5 such as ultra-wide-angle lens or even complete absence of distortion. ------------------ 3 sharp imaging Simple lens structure will naturally bring a sharper image, especially those containing the ASPH non-spherical lens fixed focus lens at maximum aperture can also provide extremely sharp focal imaging. ------------------ 4 soft coke (Bokeh)] In the same price, fixed focus lens than the zoom lens to provide a larger aperture (in fact limit the zoom lens aperture of F2.8 is), means softer bokeh blur (Bokeh) effect, apart from , the fixed focus lens aperture blades more nearly circular aperture to provide the most beautiful Bokeh. ------------------ 5 under low light conditions, the ability to adapt If you have never used the F1.4 lens, you will miss many excellent photo opportunities - in low light conditions, indoor concerts, light dark, romantic cafes, night on the streets ... However, do not recommend the pursuit of F1 .2 below the aperture, this ultra-large-aperture lens in addition to expensive, to satisfy your vanity, your work does not have any benefit. ------------------ (6) fixed-focus lens allows you to think about] The use of fixed focus lenses as wearing shackles dancing, you have to put more effort: you need to carefully pondering the composition of the way, you need to find the most suitable for your shot angle and distance, you need to start using the aperture to get the right depth of field , rather than indulge in the shallow depth of field blur ... zoom lens, it is convenient, but a fixed focus lens, your photo will be brought to another completely different level - thinking. ======================== [Zoom vs fixed focus lens] Zoom lens vs fixed focus lens of the controversy, the most fundamental is the optical quality of the dispute, the dispute in accordance with MTF curve, a lot of zoom lens MTF curve very high, and thus can be concluded that: some of the zoom lens The optical quality comparable to the fixed focus lens. Everything has an exception to a few isolated zoom in on the MTF curve shown is excellent, but the MTF does not mean that all of the optical quality. ------------- Zoom / focus lens, fixed in the design of the solution of the aberration is the same, in the aberration, 2, 3, zoom and fixed focal length can be done. However, if taken in the same aperture, the bane of the zoom lens appeared: like the curvature of field and distortion are not the opponents of the fixed focus lens. Of course, in most cases, the naked eye can not see difference. For example, when not shooting macro, curvature of field performance is not very strong, but now many zoom lens is great! Closest focusing distance of 0.38m, more than Such as TAMRON28-300XR, this lens at the 300mm end, also in the 0.49m focus, you can shoot macro. This time, bending like a field on the performance out. ------------- Visual indicators of the evaluation of the lens, some of the resolving power of the zoom lens with fixed focus lens, a ratio, color reproduction it? And the lens coating has a relatively large, so to be comparable to the fixed focus lens also. But the glare control? Zoom lens number, difficult lens number of small fixed focus lens to compete. It seems that the weakness of the zoom lens is: like the curvature of field, distortion and glare control. So, we need to be easy to say: zoom can be compared to fixed focus. I am afraid to take time. In fact, the zoom lens is the Achilles heel: the maximum aperture. The maximum aperture of the zoom lens is only f/2.8, can be extended to the longest focal length to 300, such as SIGMA 120-300/2.8. For fixed focus, greater than f/2.8 abound. ------------- (3) there is a spin theory in support of the zoom lens is better than fixed focus lens point of view: the theory test results difficult to achieve in the actual shooting, so the advantages of the fixed focus lens may not be able to give full play to its final equivalent in the zoom lens. Make sense of this theory, focusing is 98 points, zoom is 95 points in the actual shooting, focusing only played a 50% advantage for the same user with the zoom is also only can play 50% of the fixed focus is still better than the zoom. ------------- 4. General applications eliminate these primary aberrations can be complex applications need to think of a way to eliminate high-level component. Achromatic approach is to use multiple sets of lenses, adjustment Qu curvature of each lens, the spacing between the two lenses (a lens surface can eliminate an aberration, a spacing of two lenses will be able to eliminate an aberration), the other lens material is to be considered. To eliminate the seven kinds of primary aberration lens group composed of three lenses, through a series of very complex calculations (several hours) to determine each of the lens material, curvature, spacing, you can design a consumer out seven kinds of primary aberration of the lens. ========================
【Article is excerpted from: Baidu Encyclopedia】 |
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