What kind of camera do you think is used to record classes?

You'd better use a video camera when recording classes. If the budget is high, you can consider Sony X280 Z280 and so on. If the budget is not high, you can buy a camera within 10 thousand, but the pixels dare not compliment! If your course is not very long, you can consider starting a micro-list, such as Sony A7. The SLR at the same price is much better than the camera, but the SLR does not support long-term recording.