Scanning objectives can be represented by three optical characteristics, namely, relative aperture, magnification and conjugate distance. Magnification is an important indicator of scanning objective lens. Since the size of the general object is fixed, the smaller the magnification, the smaller the image surface of the lens and the shorter the focal length. Relatively speaking, the structure of the scanning system can be made smaller. , But at the same time, the higher the resolution of the lens is required.

　　The conjugate distance refers to the length between the object and the image. For the lens, it is generally hoped that the longer it is, the better. The shorter the conjugate distance, the more difficult it is to design (The angle of view increases). The schematic diagram is the same as the photographic objective lens, which is a shrinking process.

　　Design features of scanning objective:

　　1. The scanning objective lens is a small aperture and small aberration system, which requires high optical resolution.

　　2. Due to the optoelectronic device, not only the aberration of white light (mixed light) must be corrected, but also the aberration of three independent wavelengths of R, G, B must be considered.

　　3. Strictly correct distortion aberrations.

　　 It is not easy to give suggestions on 'how to choose a lens'. In fact, this largely depends on your personal budget, usage needs and the subject matter you want to shoot. The best advice is: choose the best lens you can buy. This view seems all too common, but what is surprising is that many photography enthusiasts spend a lot of money to buy a camera, but are not willing to spend money on the lens. In fact, it is not economical to do so in the long run. Without a high-quality lens, how can you achieve the full potential of the camera? There are many different brands and models of lenses on the market. Lens design buying a lens is like entering a minefield.

　　Think about what focal length SLR lens I need

　　 Only you can answer this question. It largely depends on your needs and the subject matter you plan to shoot. One of the biggest advantages of a digital SLR camera is that it allows you to not be limited to a certain focal length. You can add lenses of different focal lengths at any time to expand your photography system. Basically in the end, most photographers will build a system of different lens composition. For example, my lens system covers focal lengths from 12 mm (ultra wide angle) to 400 mm (super telephoto). Most of us are not able to buy 3 or 4 lenses at once. It may take a long time to set up your system. Please plan the order of purchase in advance.

　　 If you are still a newbie in digital SLR photography, it is best to start with a standard lens. Most new digital cameras are sold with a lightweight standard zoom lens kit. This is a good choice for those who take photos with their cameras behind their backs every day. But we all know that this kind of package lens is often relatively junior, the maximum aperture is not large enough, and the workmanship and image quality are not outstanding. Therefore, in the future, you may want a high-quality lens to replace it.

　　 Unless you plan to shoot sports or dynamic photography, is it necessary to invest in a telephoto lens with a large aperture? Often the price of this kind of lens is staggering. But most photographers want to take long-distance subjects and take them very large. So some telephoto lenses are good choices. For example, 70-optical lens 300 mm zoom lens, this focal length range is very applicable. If you have the ability to buy two lenses, you can choose a standard zoom and a telephoto zoom lens. They can basically cover the range of 35 mm to 300 mm, which is sufficient for shooting most scenes.

　　 Adding a wide-angle lens is also very practical for many photographers, especially those who like landscape photography. So a wide-angle lens can be your first choice for the next step. Once you have these commonly used lenses, you may want to buy a dedicated lens to further develop the camera's potential.

　　Independent brand SLR lenses are also a good choice

　　 Each camera manufacturer has made a series of lenses specifically for Match them with their own body. They will naturally recommend you to buy the original lens, these lenses are usually much higher than the third-party brand lens prices. So, if budget is an issue, don't underestimate those independent brand products, such as Sigma, Tamron and DZO Dongzheng Optics. Today, the workmanship and optical quality of these independent brand lenses are comparable to those produced by camera manufacturers, but they are cheaper.

　　The lenses they produce can exactly match the functions of the body (of course, it is best to test before buying), and these third-party lenses produce various mainstream camera mounts for consumption Choice, including 4/3 system. Purchasing the products of third-party lens manufacturers should not be regarded as a compromise method. This is actually a good way to maximize the efficiency of budget usage.