50D lens spare parts, that is, thin lenses at the edge of the lens, can be removed and have a shading cover. What's that thin lens for? 、

What you should say is the ultraviolet mirror.

This thing is very useful in the film age, because it is used to block ultraviolet rays, and film is very sensitive to ultraviolet rays, which will lead to deviation in color reproduction of photos, so it is necessary to block ultraviolet rays.

The digital age is different. Photosensitive elements are not sensitive to ultraviolet rays, so the core role of UV mirror is meaningless in the digital age. However, since the UV mirror has little influence on the lens light, it is now used to protect the lens.

UV mirrors can be bought in any photographic equipment store. The filter size of your Longteng 18-270 is 72mm, and any brand of 72mmUV mirror can be used on your lens.

But you should note that there is a big difference between inferior UV mirrors and high-grade UV mirrors. Mainly reflected in the following aspects:

1, inferior UV blocks more light than high-grade UV, which is simply "not transparent enough".

2. Inferior ultraviolet rays will cause more glare. Because there is an extra layer of medium in front of the lens, it is equivalent to two more reflective surfaces, which will cause more glare in the photo.

3, inferior UV will cause color difference.

Wait a minute.

To sum up, according to your budget, you can choose high-grade UV mirrors, such as Kengo pro 1D, B+W MRC multilayer coating, 300-400 yuan or so. There are thousands more high-end ones, which is unnecessary. Your lens is only over 4 thousand yuan.

On the whole, good luck!