The distance from the candle to the convex lens is 50cm-38cm= 12cm, and the focal length of the convex lens is 8cm.

2f > u > f, in the inverted and enlarged real image.

When the convex lens images, the object distance increases, the image distance decreases, and the image becomes smaller, so move the candle to the left, the object distance increases and the image becomes smaller.

So the answer is: zoom in; Small.

(2) If a fly falls on the convex lens, it only reduces the refracted and converged light, so it affects the brightness of the image, but does not affect its integrity. Because any point on the whole object is refracted and converged by the lens, a complete candle image can still be formed on the screen.

So the answer is: yes.

(3) Because myopia glasses are concave lenses, which have divergent effects on light, the light passing through the convex lens converges later than before, and the image distance is larger. Therefore, to get a clear image, it is necessary to move the screen away from the convex lens, that is, to the right.

So the answer is: Yes.

(4) Move the candle to the scale of 45cm. At this time, the object distance is 5cm, which is less than twice the focal length. In the focal length, the image is located on the same side of the convex lens, so Xiao Qiang should stand on one side of the screen and observe the image of the candle.

So the answer is: light screen.