In Johann Christoph Bischof’s “Kurzgefasste Einleitung zur Perspectiv” there are a lot of drawings in different perspectives. I think the illustrations are drawn by hand and then printed with such detailing that you could think they have been drawn directly into the book. The book has a nice alternation between text and drawings.
I like how he takes one object, for example a stair, and tries to explain the object with numbers, wideness, length and height. It shows how Johann Christoph Bischof sees the world in another way as a normal person. Some mathematicians see the world in numbers and proportions such as the golden cut which I think is the interface between nature and mathematics. Johann Christoph Bischof is one of them.
Another interesting point which i noticed, is that he alway draws the shadows of the objects on the ground. He could have put just a hatching, but i think he calculated the length of the shadow with the angle of the sun to be as precise as possible.
Because the whole book is an instruction for other people for learning to draw as he could. Thats why he had to be absolutely precise in the sketches and drawings. Actually the drawings show the reader of the book how the exercises and future drawings should be done.