Excuse me, how to set up a SLR when taking a group photo of thirty or forty people?

First of all, you must correct a mistake, the aperture problem, 5.6 is too large, and the distance is clear, so you need a small aperture. Please tell us what lens you are using if possible. Photos are usually taken in F8-F 16, which requires light. Let's talk about three points first: first, the aperture should be small, and the depth of field with large aperture is too shallow to meet the clear requirements of 40 people. Personal suggestion f11-f16; Secondly, ISO was set according to the environmental requirements at that time. If it is sunny, 100 is enough. However, if the light is bad or it is cloudy for less than 200-400 and 450D days, the film is not very good, but it is not bad. The definition is absolutely sufficient, and there is no need to rigidly limit it to 100-200. Third, the exposure is generally reduced by 1/3 and 2/3 at noon, but it is the opposite on cloudy days, because sometimes the photos are dark to ensure the shutter, and then the role of exposure compensation comes out.

I hope the above three points can help you. A tripod is a must. When shooting, people should pay attention to the best use of cable release to prevent their own breathing and other actions from shaking the camera. (also pay attention to the focal length. It is best not to take pictures at the farthest and nearest ends of the lens. The quality is the worst, it is better to drop two grades. )