Is there a big difference between a camera with a 200-focus lens and a camera with a 300-focus lens when shooting deep space? Is it possible that the 200-focal nebula is not big enough?

First of all, don't listen to that nonsense. Secondly, it is not recommended to buy expensive cameras. Buy hands, because to remove the infrared cut-off filter, daily shooting and warranty must be floating clouds. Next, choose a focus instead of the zoom lens. Deep space photography needs a flat and uniform image field, and a fixed-focus lens is usually better. Both 200 and 300 you mentioned are good focal lengths, which are suitable for the wide area and deep space of large celestial bodies. Don't worry about this difference in length, see which aperture is bigger and the picture quality is better. The aperture determines your exposure speed, and the efficiency of shooting all night depends on the aperture size. The focal length is optional 100- 1000mm (opposite the lens and telescope). No matter how long the focal length is, it is not suitable for deep space, and many large celestial bodies cannot be photographed completely. Third, choose the right equatorial plane according to the focal length of your lens. For a lens with a height of 200mm, it is best to choose the equatorial plane with a guide star.

The equatorial telescope with focal length below 200 plus Hoshino is relatively easy to use, and the large aperture is better. Super telephoto+heavy equatorial telescope is not only expensive, but also requires a lot of professional knowledge and accessories to use, and it is slow to get started.