I asked Opus 5.5 to explain camera focus by building an interactive lens lab

Here’s what it came up with after 1 hour 26 minutes in one shot, $25.66 API cost https://t.co/uqDgUs8H9h

Move the focus ring and you can see the glass elements shift the sharp plane through the scene https://t.co/pkdmmlRqU2

The Plane of Focus — a lens, opened up

Source: https://sael.net/plane-of-focus/

Where a photo turns sharp

A lens can only bringone distanceto a perfect point. Everything at that distance forms a thin sheet in the world: theplane of focus. Here it is the glowing sheet sweeping through the valley, and the bright line where it cuts the trees, the cabin and the mountains.

Why the rest goes soft

Light from any point spreads out, passes through the whole opening of the lens and is bent back together. From a pointonthe plane, the rays meet exactly on the image plane: a point. From anything nearer or farther they meet in front of it or behind it, so they arrive as a small disc, thecircle of confusion. That disc is the blur. The rings on the glass at the back show how big it is for the tree, the cabin and the peak.

The focus ring

Turning the ring slides the glass forward or back inside the barrel. Closer subjects focus farther behind the lens, so the glass moves out; far ones focus closer to it, so it moves in. Drag the ring, the slider on the console or the one in the card.

The aperture

The iris is the adjustable hole in the middle of the lens. Wide open (f/2) the cone of light is fat, the discs are big and only a thin slice is sharp. Stopped down (f/16) the cone is thin, every disc shrinks, and the sharp zone grows deep. That is why landscapes are shot at f/11 and portraits at f/2.

Upside down?

Yes. Every lens projects the world upside down, and it is drawn that way on the glass. The screens on the console flip it back, the way your camera does.

Keys

1``2``3focus on foreground, middle, background ·\[``\]nudge focus ·Faperture ·Xassembled or exploded ·Ccinematic cameras ·Rreset the view ·/hide the interface · drag to orbit · right-drag to pan · scroll to zoom ·W``A``S``Dto move,Q``Eto turn.

Numbers are for a 50 mm lens on a full-frame camera; the valley is about 60 cm away.