lens magnification experiment?

Question

there is this known Lens magnification formula:
So object to front principal point distance.
Si rear principal point to image distance
f focal length
M magnification
M = f/(So-f) = (Si-f)/f

Can someone describe an experiment to demonstrate that the Magnification for a given lens is dependent on the distance from the lens to the object. thanks in advance.

Answer 1

Get in a relatively dark room.
Put the lens in the center of your table. Well, put it in the middle of the edge of the table close to you.
Stabilize it somehow, such as by using a bean bag or wedging it between two books. Have the lens itself perpendicular to the edge of the table.
Get a white index card and rig it up somehow so it will stand up like a miniature projector screen. You can stick it in a lump of Play-Doh or clay.
Shine a flashlight through the lens so an image appears on the white card. Start by putting the flashlight about a foot away from the lens.
Move the card back and forth until the image of the bulb itself is in focus on the card.
Measure the distance from the lens to the flashlight and also from the lens to the card.
Measure the size of the image on the card.
Move the flashlight about 6 inches back and repeat.
Do this 4 or 5 times and you will see a pattern emerge in your numbers.

Good luck.

Answer 2

The camera would have a macro setting for a closer than standard autofocus range. The closeup square you are seeing is just magnifying a portion of the image in the viewfinder as an aid to manually focusing. It is not giving a portion of the image on the sensor extra magnification.