What is the projection area of the mirror?
If the sunrays dip vertically onto the mirror, the outlines of the reflection equal approximately the mirror-size. If the sunrays fall in onto the mirror from the side with flat angles, the reflex-size reduces itself to the projection area of the mirror. If the sunlight is turned around exactly by 90 degrees, the yield is reduced about a factor of 0.7. So, e. g., from a round mirror an oval reflex with an according reduction will result.
