Quill's job for the afternoon: pick the mirror for the corner of the school parking lot, so a driver can see the whole row of cars at a glance. Four elements sit in the catalog: two mirrors, two lenses.
Every element's picture is already known: six profiles, stated and collected. Choosing the element for a job is a matching read, run on that table.
A job names the picture it needs. The profiles name the picture each element gives. The selection is the match.
Read the job with three questions, in order.
First: must the picture land on a surface, or does a person look at it? Landing on a sensor, film, or screen needs a REAL image; looking needs only a virtual one.
Second: which way up, and what size? Right-way-up means upright; bigger means enlarged, smaller-but-more-in-view means reduced.
Third: does the user look INTO the element, or THROUGH it? Into means a mirror; through means a lens.
Quill's parking lot: the driver looks into something mounted on a pole, needs the scene upright, and needs a wide stretch squeezed into one view.
A reduced, upright picture with a wide field of view is the convex mirror's profile. The parking lot takes the convex mirror.
A close-up that shows a tooth enlarged and upright, looked into: the concave mirror, held inside its focal length.
Print enlarged and upright, looked through: the convex lens, held inside its focal length. A hallway squeezed upright into a door's viewer, looked through: the concave lens.
Work Quill's parking-lot choice in full.
First question: the driver looks at the picture; nothing lands on a surface. A virtual image serves.
Second question: the cars must read right-way-up, and a whole row must fit: upright, reduced, wide view.
Third question: a pole-mounted element is looked into: a mirror.
The row that says virtual, upright, reduced, wide field of view is the convex mirror's.
The parking lot takes the convex mirror.
Stellan wants his drawing to land enlarged on the classroom wall for everyone to see. Which element does the job, and how is it used?
The picture must LAND on the wall, so the image must be real.
Of the six rows, the real images are the concave mirror's and the convex lens's beyond-the-focal-point cases.
The drawing must sit behind an element the light passes through on its way to the wall: looked through, not into.
So the element is the convex lens, with the drawing beyond its focal point. The wall picture arrives inverted, so the drawing goes in upside down.
A convex lens with the drawing beyond the focal point projects it onto the wall.
A school bus needs an extra mirror that shows the driver a wide stretch of the curb, right-way-up, in one glance. Which element does the job?
Romilly wants to see a splinter in her finger bigger and right-way-up, holding a small element just above the skin and looking through it. Which element does the job?
A shaving mirror must show a face enlarged and right-way-up to someone looking into it from close up. Which element does the job?
A warehouse mounts an element at a blind corner so forklift drivers see a wide, right-way-up view of the crossing aisle. Which element fits?
Romilly builds a simple camera: light from the scene must pass through the element and land as a picture on film behind it. Which element fits?
Thora fits a viewer into a door so a person inside sees the whole hallway, right-way-up, by looking through it. Which element fits?