How to choose a Canon lens

Lens selection method First, appearance inspection 1, first check the lens box has been bumped or squeezed traces, no paint off the phenomenon;

2. Open the box and check that the accessories (such as the hood and lens cover) that you purchased with the lens are complete.

3, check the lens number (lens, warranty card, the same product number on the factory card)

4, check the lens entity whether there are trauma marks (such as bumps, scraping, etc.), whether there is a new lens taste.

5, check the bayonet, etc., the human eye is the most complete, the most advanced "instrument." For a detachable single-lens reflex camera lens, first mount the lens on the camera body to see if the lens mount is in good condition and not loose, and whether the functions (such as internal light metering, TTL auto flash, auto focus, etc.) can be Play normally.

6, check the aperture, rotate the aperture ring, the stalls should be positioned accurately, the gear is clear, retractable freely; light hole should be a regular polygon, such as: hexagonal, octagonal, nine-sided;

7, look at the glass, open the aperture, facing the light from the lens tailstock forward look, you can clearly see the inside of the lens. Brand-name lens should be clean, dust-free, glass texture should be pure, no bubbles, no cracks; open the lens before and after the cover, take the lens to a well-lit place, such as the manual lens to open the maximum aperture, the lens to the light source, view the inside of the lens Whether there are scratches, bubbles, or obvious dust particles on the optical glass. 8. Listen to the sound. Gently shake the lens. In addition to the slight ringing of the aperture, there should be no loose “click” sound from the lens.

9, feel, hand-sensing zoom and focus when there is a smooth and appropriate "damping" sense, can not be too "loose" (except when the AF lens manually focus). Adjust the zoom ring and focus ring manually, and check if there is strong friction when rotating or pushing, or if there is looseness or abnormal sound.

10. Install the lens on the camera body and check whether the AF is accurate or not. If there is abnormal noise when focusing, the lens should be free from bubbles, dust, mold, and the lens coating. There are many colors on the lens surface. (Red, yellow, blue, etc.), indicating that it is a multi-layer coating, if only the blue light Yingying monochromatic light, then the lens can not be a multi-layer coating; aperture split fresh, leaves no rust, focusing ring flexible and uniform When the zoom lens is placed upright, the push-pull ring should not slide on itself; the lens housing is fine, the surface is smooth, and there is no scratch.

Second, the physical condition inspection 1, focusing accuracy inspection, inspection, a suitable size of frosted glass placed in the camera's exposure window, so that the matte surface facing forward, and close to the exposure window plane, and then open the camera's door Or T-doors, for framing a lens resolution pattern or newspaper attached to a wall. At the same time, the position of the camera is moved back and forth until the image formed on the frosted glass is clear. Finally, the distance between the camera exposure window plane and the resolution pattern or newspaper is measured with a ruler. If the result of the measurement is equal to the focal length adjusted on the lens, the focusing accuracy of the lens is high; otherwise it is low.

When checking whether the zoom lens has a problem of distortion, the lens should be zoomed to each focal length value, and the presence or absence of distortion aberration at each focal length value should be checked in turn.

2. Pay attention to check if there are any defects in the four corners of the screen. When checking, install the camera on the camera, reduce the aperture, and use the bright object with even contrast to view and focus. Observe whether the four corners of the screen are viewed from the viewfinder. Blocked, normal lens is unobstructed. When inspecting the zoom lens, the focal length of the lens should be adjusted to each focal length value to check to see if the four corners are slightly blocked at each focal length value.

3. Note that for imaging distortion inspection, the inspection lens should be mounted on a single-lens reflex camera or a direct-view camera, and through the viewfinder, observe whether the horizontal lines or vertical lines are close to each other. If the horizontal line or vertical line of the object at the edge of the screen becomes arc-shaped, this lens has a distortion aberration. The greater the deformation of the straight line, the more serious the distortion. Look at the window of the camera in the direction of the store. If the lines of the square are bent after being imaged, it means that the lens has been distorted. Under normal circumstances, the wide-angle lens barrel distortion; telephoto lens pillow distortion; standard lens should not have obvious distortion. When inspecting the focus accuracy of the subject at infinity, the focal length of the lens should be adjusted to the infinity mark to see if the image on the frosted glass board is the sharpest; if it is clear, the focusing accuracy is high; if it is clear A poor degree indicates that the lens has a low focusing accuracy.

4, on the uniformity of the illumination of the image field inspection, such as field illumination uneven defects, the vast majority of short shots. Therefore, when you purchase a short-range camera lens, you should attach it to the corresponding single-lens reflex camera. Facing the even-brightness object, observe the brightness of the center and the four corners of the screen through the camera's viewfinder. If the center is bright and the corners are dark, it means that the illumination intensity of the image field is not uniform, and the center of the screen image captured by the lens is high in density and the density of the four corners is small.

5, check the identification rate, from the viewfinder to observe the scene, when the focus is good, the edge of the scene is very clear, the lens identification rate is high; if you look vague, even if the red or blue lines, then the lens dispersion Serious, poor discrimination.

6, check the coefficient of flare factor, the weather is very bright, neither smoke nor fog, if you look at the viewfinder in the scenery there is always a sense of gray, then the lens stray light, the quality is not good; as seen in the viewfinder The scene has good transparency and is very clear, indicating that the lens is of good quality.

7, check the color reproduction, the color reproduction of the lens is very important for taking vivid photos. To check the color reproduction, first remove the lens from the camera body, remove the lens cap, open the aperture to the maximum, take a white paper behind the lens, face the fluorescent lamp of the store, and look through the lens and project to white. Whether the fluorescent lamps on the paper are as white as the original ones are not color cast. This difference is very small, to be seen carefully. If there is a large difference in color, poor color reproduction, quality times.