What are the powers of the objectives?

Answer 1

The field for the high power objective is very small, so if you do not have the organism or whatever you want to view in focus on a lower power, it may be very difficult to find on high power. Also, the lens for the higher power objectives are longer than the lower ones, which makes them closer physically to the slide that you are viewing than the lower objectives. Thus you must use the fine tuning knob to sharpen the image in high power, because you could break the slide if you use the course adjustment knob.