Panasonic professional LCD laser projector modified short-focus lens, throw ratio range 0.5-4.8: 1
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Basic knowledge of projector lens

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Author : 周巍衡
Update time : 2020-10-16 11:09:03

Basic knowledge of projection lens

Projection lenses generally refer to replaceable engineering projection lenses used on professional projectors.

Generally, consumers are divided into the size requirements of the projector installation distance and the size of the playback screen

Short focus: large screen shots in short distance, such as laser TV, museums, science and technology museums and other spaces with relatively small installation distances

Middle Jiao: Generally used in school classrooms, conference rooms, auditoriums, etc.

Telephoto: generally used for architectural projection, theater, stadium, etc.

Special scene application lens: reflective projection lens 120-180 degree fisheye lens

Throw ratio:
1. Throw ratio is a common parameter of projection, which is the distance from the lens to the screen divided by the width of the screen.

​​2, can be calculated by formulas, you can know the relationship between the projector lens and the screen size, and the screen distance to facilitate the construction staff to locate the projector installation location.

Projection distance = the width of the projector screen X the focal length of the projector lens

Set out by the formula: the width of the projector screen = the projection distance ÷ the focal length of the projector lens

The focal length of the projector lens = projection distance ÷ projector screen width

For example: if the projector needs to project 100 inches at a distance of 10 meters, which projector lens should be used?

We can calculate it like this: 10 (meters) ÷ 2.03 (meters) = 4.9 (this is the projection ratio of the projector lens, just one digit after the decimal point)

It can be concluded that the required lens is a telephoto lens as long as the throw ratio range includes 4.9:1 to meet the demand

The meaning of f and F on the projection lens:
1. F is the transmittance of the lens. The smaller the F, the better the light transmittance of the lens. It is better to achieve F1.7 mostly standard lenses. Short throw general F2.0 F2.2 F2.4 F2.5

2. f means that the shorter the focal length of the lens, the smaller the throw ratio, and the larger the throw ratio, the larger the throw ratio.

3. The fixed focus lens generally has one F and one f, and the zoom lens has a range value.

Fixed focus and zoom:
1. A fixed-focus lens has only one projection, such as 0.73:1, a focal length, and an F. The size of the projection screen cannot be changed, and only four corners can be fine-tuned.

2. The zoom lens has a throw ratio range such as 0.85-1.45:1, a focal length range, and an F variable range. The projection screen can be made larger or smaller.

Resolution and resolution:
1. The projection lens is being upgraded with the development of projection chip technology

For example, the resolution of the projection chip is 1024*768 1280*800 1920*1200 2840*2160

Projection lenses also have corresponding resolution standards. High-resolution lenses can be downward compatible, and low-resolution lenses cannot be upward compatible.

2. The higher the resolution, the higher the requirement for the resolution of the lens. If the high-resolution chip projector is installed with a low-resolution lens, the playback effect will only be the effect of a low-resolution projector, so the resolution of the projector chip It is compatible with the resolution of the projection lens, otherwise the screen effect of the projector will be seriously reduced.


Generally speaking, it is the range where the picture can move up, down, left, and right after the lens of professional engineering projector is installed, which is convenient for construction personnel to install the projector. It does not need to be installed particularly accurately. Generally, the displacement of standard lens and telephoto lens is large, up and down 50%, left and right 15% about. Short-focus lens has less displacement, 20-30% up and down, 10% left and right

Support brightness:
Professional engineering projectors have developed rapidly from 5,000 to 40,000 lumens since 2010. The light source ranges from ultra-high pressure mercury lamps to laser light sources. The higher the brightness, the higher the requirements for projection lenses.

Therefore, every 5000 lumens has different requirements for the projection lens material. When choosing a projector with 7000 lumens or more, you need to ask the supplier whether the lens supports high lumens, otherwise the lens may burn out or the image may be unstable.

Out of focus and virtual focus
Out-of-focus: Generally refers to the clear adjustment of the screen. After working for a period of time, the projection screen on the four corners or one side extends a few pixels to the periphery. This is caused by the physical phenomenon that the lens expands and shrinks due to heat during the projection work.

Generally, running 1-3 pixels at home is qualified. In engineering, high-end projection can generally control the running within half a pixel.

Fictitious focus: Generally refers to the clear adjustment of the picture. After working for a period of time, the whole picture or a certain area of ​​the picture is unfocused and needs to be refocused. This is caused by the physical phenomenon of the lens being heated and contracted during the projection work. It is also that this lens does not support such a high projector brightness, or the projection lens shifts too much, which is caused by uneven heating of the projection lens. It is recommended to replace the lens.

Lens 9-point brightness and uniformity
The brightness of the projector: "light out" is the main technical indicator of the projector, and "light out" is usually expressed in terms of luminous flux, which is the ability to describe the intensity of the visual response generated by the light source radiation per unit time, in lumens. The international standard unit of the projector's luminous flux is ANSI lumens. ANSI lumens is a method for measuring the projector's luminous flux established by the American National Standards Institute. The measurement environment is as follows:

1. The projector is turned on for half an hour with a full white screen. When playing a 60-inch screen, the zoom lens needs to test both the maximum throw ratio and the   throw ratio. There will be a big difference in brightness because the F value and light transmittance are different under different throw ratios.

2. Use a luminance meter to measure the illuminance of each point on the nine intersections of the "tian" shape on the screen, and multiply it by the area to obtain the luminance of the 9 points of the projection screen.

3. Find the average of the brightness of 9 points, which is ANSI lumens, which is the lens.

4. Then divide the brightness of 9 points by the percentage of the highest brightness of the 9 points, and the percentage obtained by dividing by 9 is the 9-point uniformity. Generally, 90% brightness uniformity is excellent.

5. The consequences of poor brightness uniformity at 9 points, especially in multi-machine splicing and fusion, the fusion belt is obvious

Lens decay
Under normal circumstances, the standard lens that comes with the projector is the most suitable lens considered by the manufacturer. The 9-point brightness and 9-point uniformity of the maximum throw ratio and the  throw ratio can be tested as the test standard. Then change to another lens to compare whether the brightness is higher or lower than the original lens. Generally, the 0.8:1 short focal length is 10-20% lower than the standard lens, and the 0.8:1 lower focal length is 20%-50% lower than the standard lens, and the telephoto lens Higher or flat than standard lenses.

Lens cast
Generally, it refers to the partial deviation of the color of the projected image, such as a yellowish left side of a white image or a normal red right side.

It does not matter if you use a single machine, but it is fatal when multiple machines are used for splicing and fusion. The lack of color in the picture is obvious.

Lens leakage
Generally, the lens is designed to pursue the highest brightness and does not match the design of the projector chip, resulting in a red spot on the corner of the projected picture and a white aperture around the picture. The contrast is very low when using full black in the project.

Red band

Aperture where light leakage appears

1. Since the lens contains precision parts, do not subject to severe vibration or overload

2. When transporting a projector with a lens, the lens needs to be removed before transport. Improper handling during transportation can damage the lens and displacement system.

3. Before removing or installing the lens, be sure to turn off the projector, wait until the cooling fan stops running, and unplug the power cord.

4. Please do not touch the surface of the lens when removing or installing the lens.

5. Prevent fingerprints, dust or oil from adhering to the lens surface. Please do not scratch the surface of the lens.

6. When using lens components, set the lens shift to the center of the screen.

7. When the lens shift is adjusted to other unexpected positions in the center position, the edge of the image may become dim or cause black shadows. Please adjust the shift to avoid black shadows, otherwise the lens lens group will be damaged.

Please indicate the source for reprinting

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